Module 6 Mendelian Genetics

Module 6 - Mendelian Genetics

Introduction

You expect to look like your parents and your other ancestors, yet you are a little bit different. A monk in a garden discovered how species and individual traits are inherited. If it weren’t for Gregor Mendel and the garden pea, genetics might still be in the Dark Ages. Using this simple organism, Mendel developed evidence for the basic principles of genetics. In this Module, you will explore the concepts of dominance, segregation, and independent assortment. You will analyze ratios and probabilities of genotypes and phenotypes to examine many other possible ways of transmission of traits from generation to generation. You will discover how variability can be dependent on the number of genes involved in a trait, crossing over, and gene linkage. You will also learn why some traits like hemophilia are more common in males than in females. There are many tools that can be used to study the transmission of traits, and you will have the opportunity to use these tools in your study of some common heritable traits.

Think about the following question as you complete this module:

• What are the basic rules and steps involved that effect the transmission of genetic characteristics to the next generation?

• In This Module

• Lesson 1: Theories and Terminology of Inheritance

  In this lesson you will explore and become familiar with the language of genetics. You will be introduced to a nineteenth century monk, Gregory Mendel, and learn why he is considered the Father of Genetics.

  You will consider the following essential questions:

  • What is the basic language of genetics?
  • How does the work of Mendel explain the basics of Classical Genetics?

  Lesson 2: Mendel’s Laws and Monohybrid Crosses

  In this lesson, you will learn the patterns of inheritance that Mendel first discovered in pea plants. You will become familiar with techniques and conventions used by geneticists to trace the inheritance of traits from one generation to the next.

  You will consider the following essential questions:

  • What are the simple principles of single trait inheritance?
  • How can genotype be determined from phenotype?

• Lesson 3: Multiple Alleles and Incomplete Dominance Crosses

• In this lesson, you will explore traits that do not follow Mendel’s patterns of simple dominance, but can still be explained by his laws. You will understand how genes can have more than two alternate forms.

  You will consider the following essential questions:

  • What happens when one allele is not completely dominant over another?
  • How does having more than two alleles for a gene affect the possible phenotypes for a trait?

  Lesson 4: Dihybrid Crosses

  In this lesson, you will learn how to follow the inheritance of two separate traits at the same time. As you follow two traits at once, you understand how the movement of alleles for one trait, does not effect the other trait during the formation of gametes.

  You will consider the following essential questions:

  • How do scientists track the inheritance of more than one trait at a time?

  Lesson 5: Probability

  In this lesson, you will learn how to predict the genetic outcome of future generations by examining numbers and ratios. Patterns can give the likelihood of a trait remaining hidden or being expressed.

  You will consider the following essential questions:

  • How can ratios be used to analyze types of inheritance or to predict the possibility of a trait appearing in the next generation?

  Lesson 6: Chromosomal Theory and Sex-linked Inheritance

  In this lesson, you will begin to explore inheritance patterns that do not follow Mendel’s laws. You will see how some traits occur more frequently in one gender over another, and are said to be linked.

  You will consider the following essential questions:

  • Why do some traits appear more frequently in one gender than the other?
  • How did Thomas Hunt Morgan’s work provide experimental support for the chromosomal theory of inheritance?

  Lesson 7: Genes and the Environment

  In this lesson, you will examine the effect the environment may have on the expression of genes.

   

  You will consider the following essential questions:

  • How does the environment affect the expression of genes?

  Lesson 8: Polygenetic Traits

  In this lesson, you will study traits that are controlled by many genes. You will recognize inheritance patterns that have gradual changes in phenotypes, and you will understand that the expression of one gene can turn the expression of another on or off.

  You will consider the following essential questions:

  • How might multiple genes combine to form a single trait?

  Lesson 9: Crossing Over Frequencies and Gene Mapping

  In this lesson, you will learn how genes that are found on the same chromosome tend to move together, and are thus said to be linked. Using your understanding of crossing over from meiosis, you will learn how this allows scientists to map the relative location of genes that are found on the same chromosome.

  You will consider the following essential questions:

  • How does crossing-over in chromosomes relate to finding the position of genes?
  • What is the importance of knowing the location of specific genes on a chromosome?

  Lesson 10: Plant, Animal, and Human Genetics

  In this lesson, by learning to create and analyze pedigrees you will be able to track the inheritance of rare genetic diseases through families.

  You will consider the following essential questions:

  • What technologies exist to help us explain and predict the inheritance of traits in breeding programs and/or family histories?

Big Picture

Has it ever been suggested that you may look like or have a similar trait of someone else in your family? You have your mother’s eyes, or your grandfather’s hairline? If all the men in the family were balding, would that worry you?

In your family, you may wonder why some look alike and some do not. Or why some have inherited certain traits or genetic conditions, and some have not. As you look around and notice the variety of traits in your family, you may wonder what determines how and why each member got their unique characteristics.

This begins the journey towards understanding the rules and steps involved in the inheritance of traits and how they are expressed. Through this journey you will consider various examples of inheritable characteristics and how they are transmitted from generation to generation.

Essential Questions

This module will explore these essential questions:

• What controls the physical appearance of organisms?

• How are traits inherited from generation to generation?

• How can the analysis of ratios and probabilities of the external appearance of traits reveal the internal workings of genetics?

• What tools can scientists use to study and predict inheritance?

• Why do some traits appear more frequently in males than in females?

• How can offspring demonstrate gene combinations never seen in their parents?

• Does inheritance of traits always happen the same way?

Lesson 3.6.1

Get Focused

A prize pumpkin at a county fair must be large, well-shaped, have good orange colour, and be disease-free. These descriptors are called characteristics, and gardeners that wish to compete in these competitions are constantly selecting plant seeds that come from vines that demonstrate more of these qualities than others. Breeding plants or animals to reflect desired features or behaviours is called selective breeding, and has been going on for as long as history has been recorded.

Just how those characteristics are passed on from one generation to the next has not been known for nearly as long. How characteristics are passed on is the focus of genetics, the study of inheritable traits.

In this lesson, you will explore and become familiar with the language of genetics. You will be introduced to a 19th century monk, Gregory Mendel and learn why he is considered the Father of Genetics.

In this lesson, the following focusing questions will be examined:

• What is the basic language of genetics?

• How does the work of Mendel explain the basics of Classical Genetics?

This lesson will take approximately 60 minutes to complete.

 There is no assignment for this lesson. 

The other questions and activities in this lesson are not marked by the teacher; however, you should still attempt all of the work offered here. They are designed to help you review important information and build key concepts that may be applied in future lessons.

Here is a tutorial video for this lesson that you can watch if it suits your learning style.  Bio30 tut#3.6.1 Mendelian Genetics

3.6.1 page 2

Explore

Read

Early Theories

Farmers have always known that keeping seeds back from good crops, or breeding prize cows or chickens, helps to improve the next generation’s chances of yielding better numbers and/or favorable traits, or of being better in some other way. However, just exactly how favorable traits are passed on has been the interest of scientists for centuries. Early theories tended to give importance to the kind of life the parents lead. Similar to Lamarkian’s ideas of evolution where body parts change in response to use, many early scientists believed life’s experiences affected the next generation’s traits. These theories were finally put to rest by a 19th century Austrian monk named Gregor Mendel. Mendel studied garden peas as his experimental subjects and, with breeding and observation, laid the foundation of our current knowledge and understanding of heredity.

Read the sections on “Early Theories of Inheritance” and “Developing a Theory of Inheritance: Gregor Mendel’s Experiments” in your textbook on pp. 586–588. When finished your reading, answer the following questions for your own understanding and save the answers into your course folder.

1. Where did Aristotle believe the factors for inheritance were located in the body? How did he believe these were passed down?

2. What were some of the likely problems early scientists must have encountered when trying to explain inheritance?

3. Examine the seven traits Mendel studied on p. 588. What do you notice about all of them?

4. What is a monohybrid cross?

5. Explain how a hybrid plant is different from a true breeding plant.

6. Explain the difference between P, F1, and F2 generations in a cross.

Watch and Listen

Consider the first part of the following video on Classical Genetics and Monohybrid Crosses. (15 minutes). Begin the video and continue watching until you reach the section “Bio Challenge: Round vs. Wrinkled Peas.” Answer the following questions for your own understanding and save the answers in your course folder.

1. Who discovered that cells differentiate during embryo development and disproved the idea that the egg or sperm held a complete miniature organism?

2. Explain the meanings of the terms dominant and recessive factors (we now call factors alleles).

3. Distinguish between the terms gene, allele, and chromosome.

4. What process creates gametes?

5. How do we distinguish between dominant or recessive alleles when drawing them on a chromosome or in a Punnett square.

6. What does it mean to be homozygous for a trait? How is this different from being heterozygous for a trait?

7. Using an example, distinguish between the terms genotype and phenotype.

Web Search

The following video reviews Mendel’s experiments.

1. Why did Mendel choose to study pea plants in his experiments?

2. How did he ensure that his plants were true breeding?

3. What does Filial mean?

4. How did Mendel make sure his results were statistically accurate?

3.6.1 page 3

Read

As the video clip has already introduced, Mendel discovered two variations of traits for each characteristic that he studied. One trait is dominant over the other. The evidence for this was discovered when he crossed two pure plants with contrasting traits, such as Tall (T) or short (t) plants for example. The first generation plants, or F1, were all Tall. The short trait seemed to disappear. However, when these plants self fertilized, their offspring, the F2, were a mix of Tall and short plants. Read the section “Dominant and Recessive Genes” in your text on page 588 for a better understanding of this mode of inheritance.

Mendel proposed that each trait was controlled by factors. We now call these factors genes, and the different forms of genes are termed alleles. Each plant will have two alleles present for each characteristic, and will pass down only one of these alleles when they create gamete cells (Sperm or egg). The combination of the two alleles received by a gamete is random, and this type of separation is known as Mendel’s first law; The Law of Segregation. For a greater understanding of this law, please read “The Law of Segregation” in your text on page 589.

Self-Check

Complete the following set of questions to see how much of these genetics concepts you have begun to internalize!

1. Separate the 2 chromosomes by meiosis

2. What type of cell is formed as a result of meiosis?
3. What term is used to describe “T” and “t”?
4. Which of Mendel’s Laws does the above example illustrate?

2. Place the appropriate term in the space provided for each picture. Use the following words: genotype, phenotype, segregation.
   
            Blue eyes                           bb                               
   a. _______________          b. ________________        c. __________________
3. Indicate whether each of the following is a trait or a characteristic:
   
   
   1. wrinkled seed
   2. curly hair
   3. pod color
   4. plant height
4. How many different types of gametes would an individual with the following genotypes produce (hint: each gamete will contain only one from each letter pair):
   
   
   1. AABBCC
   2. AaBbCc
   3. AaBbCC
5. What are the gamete types produced by an individual with genotype WWTtPp?
6. What evidence is there for Mendel’s principle of dominance?
7. Which term identifies or describes these genotypes:
   
   a) Rr/Pp –                          b) RR/PP –

3.6.1 page 4

Reflect and Connect (optional)

Study Dictionary or Flash Card Set - Assessment

Learning to communicate in another country would be tough without knowing a few terms in the local vocabulary. Working in genetics is much the same. To help you in your study of genetics, let’s take the time now to work through all of the new terms you will need to understand. Using the new terms from Chapter 17 (identified by the bold type) in your text, create a flash card study set. This could be in the form of a power point presentation, an online flash card set, or a traditional 3x5 paper card stack. Write the term on one side, and your definition on the other. If you chose to do an electronic version, save a copy to your course folder and find out from your instructor if there is a way you can share your set with your classmates.

Use your flashcard set to review and study the vocabulary. Record the amount of time it takes for you to complete the flashcards and repeat the process until you can quickly move through all of the cards. You may also record the number of times you answer correctly for each attempt and repeat the activity until you increase your accuracy.

Going Beyond

Write a fictional story while attempting to incorporate as many of your new vocabulary words as possible. After your first draft, complete a revision that forces you to add the words that you did not use in your original draft. Save your story to your course folder and post it to your class discussion area.

Lesson Summary

During this lesson you were to focus on the following questions:

• What is the basic language of genetics?
• How does the work of Mendel explain the basics of Classical Genetics?

By reading and watching the videos you have heard the language of genetics being used. With your creation of a study dictionary, or flash card set, you should now have begun to put that language into practice. Keep reviewing your flashcard set, and pay attention to any new words that will be presented in upcoming lessons.

Mendel used careful scientific methods to analyze the inheritance of traits in garden peas. He made clear observations, conducted many experimental trials, and worked in a controlled environment. It is thanks to his work that we have been able to begin to understand just how genes are responsible for our characteristics.

Diploma Connection

Answer the following questions from a previous Biology 30 Diploma Exam.

1. Alternate forms of the same gene are known as
   
   
   1. alleles
   2. gametes
   3. genotypes
   4. heterozygotes
2. Mendel’s principle of segregation states that alternate forms of a gene separate during
   
   
   1. fertilization
   2. seed dispersal
   3. cross-pollination
   4. gamete formation
3. An organism is heterozygous for two pairs of genes. The number of different combinations of alleles that can form for these two genes in the organism’s gametes is
   
   
   1. 1
   2. 2
   3. 4
   4. 8

Use the following information about tobiano twin colts to answer the next question.

Descriptions and Symbols Used to Represent One Type of Coat Colour in Horses

Numerical Response

4.   Using the numbers above, match these descriptions and symbols with the term below to which they apply.

Description or

Symbol Number:       _____             _____             _____             _____

Term:                   gene               allele               phenotype      genotype

Lesson 3.6.2

Lesson 2—Mendel’s Laws and Monohybrid Crosses

Get Focused

Has anyone ever told you that you look just like your mother, your father, or your great uncle Jed? While the question of how we got many of our physical traits can be complex to explain, a few are very simply explained. Traits like hair-line, thumb curve, and earlobe attachment are examples of traits that are controlled by one gene with two alleles. Comparing which traits your parents have to those you and your siblings have is a quick way to observe inheritance in action. 

In this lesson, you will learn the patterns of inheritance that Mendel first discovered by studying pea plants. You will become familiar with techniques and conventions used by geneticists to trace the inheritance of traits from one generation to the next.

In this lesson, the following focusing questions will be examined:

• What are the simple principles of single trait inheritance?

• How can genotype be determined from phenotype?

This lesson will take approximately 80 minutes to complete.

Module 6: Lesson 2 Assignment

  After you work through the lesson, complete the online assignment.

Bio30 3.6.2 online assignment

The other questions and activities in this lesson are not marked by the teacher; however, you should still attempt all of the work offered here. They are designed to help you review important information and build key concepts that may be applied in future lessons.

3.6.2 page 2

Explore

Here is a video for you to watch:

Crash Course - Heredity

Read

Recall that Mendel worked with seven contrasting traits. Each trait was controlled by a single gene, and each gene had two alternate forms known as alleles. These alleles related to each other as either dominant or recessive. Dominant alleles are always expressed, and show up in the phenotype of either homozygous dominant or heterozygous individuals. Recessive phenotypes can only be displayed when there are only copies of recessive alleles present, thus only in homozygous recessive individuals.

In working with genetic problems, it is very important to understand how alleles move, and how they are expressed. Mendel’s first law: The Law of Segregation, states that each allele pair in the parents is separated in the creation of gametes. This separation is random. Further, these gametes unite with other gametes in an equally random way. This ensures that all possible combinations of gametes will show up in the offspring. To ensure that this is done, geneticists use a Punnett square. Read about how to represent alleles properly, and then how to create and use Punnett squares in your text on pages 589 and 590.

Watch and Listen

Let’s continue watching the following video on Classical Genetics and Monohybrid Crosses. (10 minutes). Begin the video at the section “Bio Challenge: Round vs. Wrinkled Peas," and watch until the end. Answer the following questions for your own understanding, and save your answers in your course folder.

1. Explain Mendel’s first law in your own words.
2. What does a Punnett square tell you in a cross?
3. Given two heterozygous parents for Pea type (Rr), what are the phenotypic and genotypic ratios expected in their offspring?
4. What does a test cross help determine?

Try This

Examine the sample on how to build a Punnett square on the bottom of page 590 of your textbook. Notice how they write the gametes of one parent along the top of the Punnett square, and the gametes of the other parent down the side. This way, the square can be filled in by carrying the appropriate letter across or down as shown.

Using this as a guide, answer practice problem #1 on the bottom of page 591. Create a Punnett square to illustrate the Parental cross, and another one to illustrate the F1 cross and the resulting F2 generation. Save your answers to your course folder.

Watch and Listen

The following video discusses Mendel's law of segregation. 

1. Did any of Mendel’s traits blend in the offspring?
2. What is the F2 ratio of dominant to recessive phenotypes in all of Mendel’s traits?
3. What are the phenotypic ratios for a test cross if the test plant is heterozygous? If it is homozygous?

Module 6: Lesson 2 Assignment—Lab

Crossing pure breeding plants or animals with contrasting traits or phenotypes can help demonstrate how dominant and recessive genes work.

You will complete a Gizmo on Mouse Genetics (One Trait) and all of the activities indicated in the lab. You will be prompted to complete the Module 6: Lesson 2 Assignment in the lab.

3.6.2 page 3

Lesson 2 Lab: Mouse Genetics (One Trait)

Many traits have two clear phenotypes, like tall or short pea plants. Sometimes these traits are controlled by a single gene with two different alleles. One is dominant, and the other recessive. When an organism has two copies of the dominant allele, or one dominant allele and one recessive allele, the dominant trait is expressed (tall plants). Only when the organism has two copies of the recessive allele does the recessive phenotype come through (short plants).

In this simulation you will explore mouse coat colour as a single gene trait. You will conduct various breeding cycles until you understand how dominant and recessive alleles work, and until you understand how to determine a mouse’s genotype from test crosses and from observation of phenotype.

Problem (Purpose)

Manipulate the P1 breeding pair and observe the resulting offspring to determine how dominance and recessive alleles create a recognizable inheritance pattern. How can understanding this pattern allow you to predict the outcome of various new crosses? How can the results from a cross determine the genotype of the parents?

Materials

For this simulation you will require access to the Internet and a word processing program to record your results.

Procedure

Open up the following link to the Mouse Genetics (One Trait) Gizmo.

 Put your username and password into the top login box. Locate the “Exploration Guide” by clicking on the lesson info button in the top right hand corner. 

In this investigation, you will follow the instructions listed in the exploration guide for the parts titled:

• Observing Patterns of Inheritance.
• Predicting Genetics Crosses

As you read and follow the instructions, make sure you are able to answer the questions listed for yourself. Some of them will be repeated later in this lab for you to submit to your instructor.

Observation
The top two spots in the Mouse house are the P1, or parental generation. Whichever two mice you place here will breed to create the other five spots you see in the mouse house (the F1 generation). You can place either two black or two white mice as parents to start. What kind of offspring result? Does it matter how many times you click “breed”? The next pair of parents should consist of one white and one black mouse. What offspring result now? Now keep two F1 mice by dragging them into the cages at the bottom. Then clear the house with the “clear” button and drag the two from the cages up into the top breeding spot. Click “breed” to generate the next group of offspring (the F2 generation). What kind of offspring may result from this cross? Breed this group until you get a few mice of both colours in the offspring, or F2.

Module 6: Lesson 1 Assignment

Retrieve your copy of Module 6: Lesson 2 Assignment that you saved to your computer earlier in this lesson. Complete the assignment. Save your completed assignment in your course folder. You will receive instructions later in this lesson on when to submit your assignment to your teacher.

3.6.2 page 4

Read

Phenotypically dominant individuals can either be homozygous dominant or heterozygous. There is no way to determine which genotype they have simply by looking at them. To help with this problem, geneticists conduct test crosses. Read about what a test cross is, and how to set one up, on page 591 of your text.

Reflect and Connect

Study Dictionary or Flash Card Set

Retrieve your genetic dictionary and add all of the new terms from this lesson to your work. Spend a few minutes reviewing and strengthening your grasp of this language.

Self-Check

One of the essential skills in genetics is learning to apply what you know to new situations. On the following website there are 13 monohybrid cross problems to analyze. For now, you should only consider problems 1–8. Each problem is designed to have you take a fact or discovery you’ve read about and apply it to a new situation. As you work through each problem, notice that there is a link to help or to a tutorial from within each one. These are excellent review links, and you may use them often if you find that you are stuck. Follow the link below to the index and work through problems 1–8.

Module 6: Lesson 2 Assignment

Submit your completed Module 6: Lesson 2 Assignment to your teacher for assessment.

3.6.2 page 5

Lesson Summary

During this lesson you were to focus on the following essential questions:

• What are the simple principles of single trait inheritance?

• How can genotype be determined from phenotype?

Mendel worked with seven contrasting traits in peas. Each trait was either dominant or recessive; there was no blending in his work. You have learned that dominant traits will be expressed in either homozygous dominant or heterozygous plants, while recessive traits can only be seen in homozygous recessive plants. You have also learned how to predict the genotypes and phenotypes of offspring using a Punnett square.

Since dominant alleles can hide recessive ones, breeders and farmers are most interested in working with homozygous or true breeding individuals. This ensures the continuation of desired traits. Since genotypes can not be seen, but only inferred from probabilities, setting up a test cross is an excellent way to determine genotype. In a test cross an individual with the recessive phenotype is crossed to an individual with unknown genotype displaying the dominant phenotype. The results of the cross will indicate if the unknown was either heterozygous or homozygous. If all resultant offspring express the dominant trait, then the parent of unknown genotype is homozygous dominant. However, if half of the offspring express the recessive trait, then the parent of unknown genotype is heterozygous.

Diploma Connection

Answer the following questions from a previous Biology 30 Diploma Exam.

Use the following information to answer the next question.

Farmers who raise sheep for wool try not to produce offspring with black wool. Black wool is very brittle and difficult to dye; therefore, white wool is more desirable. If a farmer purchases a white ram, he will generally carry out a test cross to determine whether the ram is heterozygous or homozygous for white wool. White wool (W) is dominant to black wool (w).

1. If the ram is heterozygous for white wool, the expected phenotypes of the offspring of the farmer’s test cross would be:
   
   
   1. all black
   2. all white
   3. 1/2 black and 1/2 white
   4. 3/4 black and 1/4 white

Use the following information about tobiano twin colts to answer the next question.

Descriptions and Symbols Used to Represent One Type of Coat Colour in Horses

2. What are the genotypes for coat colour of two horses that are predicted to produce offspring in a 1:1 genotypic ratio?
   
   
   1. Tt and tt
   2. Tt and Tt
   3. Tobiano and tobiano
   4. Tobiano and not tobiano

Use the following information to answer the next question.

Sickle cell anemia is an autosomal recessive genetic disorder. Because individuals affected by sickle cell anemia have defective hemoglobin proteins, their blood cannot transport oxygen properly. There appears to be a relationship between the incidence of malaria and sickle cell anemia. Individuals with sickle cell anemia and carriers of the sickle cell allele have some resistance to malaria. Malaria is caused by the parasite Plasmodium, and is transmitted between humans by mosquitoes.

3. The probability of two carrier parents having a child with sickle cell anemia is:
   
   
   1. 25%
   2. 50%
   3. 75%
   4. 100%

Cystic fibrosis is the most common genetic disorder among Caucasians, affecting one in 2 000 Caucasian children. The cystic fibrosis allele results in the production of sticky mucus in several structures, including the lungs and exocrine glands. Two parents who are unaffected by the disorder can have a child with the disorder.

4. A girl and both her parents are unaffected by the disease. However, her sister is affected by cystic fibrosis. The genotypes of the mother and father are:
   
   
   1. both homozygous
   2. both heterozygous
   3. homozygous and heterozygous, respectively
   4. heterozygous and homozygous, respectively

Lesson 3.6.3

Lesson 3—Multiple Alleles and Incomplete Dominance Crosses

Get Focused

Life is rarely black and white or, in the case of flowers, red and white! Instead, many physical characteristics observed in plants, or in people, have a variety of phenotypes; certainly more than the two that can be accounted for by Mendel’s dominant and recessive inheritance pattern. While our study of genetics could very quickly become more complex, there are two ways we can add a bit of variety and still use Mendel’s simple laws to explain them. Staying with monohybrid crosses, we will consider multiple alleles and incomplete dominance. By examining these two new inheritance patterns, you will be able to explain a little bit more of the variety you see around you.

In this lesson, you will explore traits that do not follow Mendel’s patterns of simple dominance, but can still be explained by his laws. You will also come to understand how genes can have more than two alternate forms.

In this lesson, the following focusing questions will be examined:

• What happens when one allele is not completely dominant over another?
• How does having more than two alleles for a gene affect the possible phenotypes for a trait?

This lesson will take approximately 80 minutes to complete.

Module 6: Lesson 3 Assignment

You will complete a lab on chicken genetics for assessment.  You will then complete the online assignment for this lesson.

Bio30 3.6.3 online assignment

The other questions and activities in this lesson are not marked by the teacher; however, you should still attempt all of the work offered here. They are designed to help you review important information and build key concepts that may be applied in future lessons.

Here is a tutorial video for this lesson that you can watch if it suits your learning style.  Bio30 tut#3.6.3 Exceptions to Mendel

3.6.3 page 2

Explore

Read

Larissa's tomcat Smokey was her pride and joy; dusty grey with chocolate brown spots, he was unique to the neighbourhood. One day a new family moved in next door. To Larissa's surprise they had a female cat, also grey with chocolate spots. When the neighbours discovered Larissa's cat, they immediately requested its siring services. They wanted to breed her cat to their cat. Ten weeks later, the female gave birth to six kittens. Hopes of the unique grey and chocolate combination were dashed as only one kitten, a male, showed the parental colors. Four kittens were solid grey, and a fifth was completely white.

Why are there three phenotypes in this case instead of two as was the case in all monohybrid crosses studied so far? Here is a curious genetic phenomenon inconsistent with Mendel's observations. What is the explanation?

Read the section of your text entitled “Incomplete Dominance and Co-dominance” on pages 594 and 595 of your text. When finished your reading, answer the following questions for your own understanding and save the results in your course folder.

1. Four-o'clock flowers occur in two pure-breeding varieties, one with white flowers and the other with red flowers. If these are crossed, all of the F1’s have pink flowers. Give the genotype of each parent, and the genotypes of the F1's of such a cross. Use R1 and R2 to represent the alleles for red and white respectively.

2. The phenotype of the F1's is pink flowers that appear to be a blend of the two originals. It is an intermediate type.

3. How does the phenotypic ratio change for a monohybrid cross with no dominance, as compared to a Mendelian cross where there is dominance?
4. In the case of co-dominance and incomplete dominance, pure-breeding individuals are easily identified. Explain this statement.
5. Use a Punnett square to find the probability of producing a blue roan horse if you cross a roan with a black stallion.
6. Can you generally explain the results of breeding Larissa's tomcat with the neighbour's spotted cat?

Watch and Listen

Consider the following video on Alternate Patterns of Inheritance: the Potential for Diversity. (about 15 minutes). Begin the video and continue watching until the section “Bio Simulation: Inheritance Case”. Skip a few sections and then watch the “Incomplete Dominance” section. Answer the following questions for your own understanding and save the results in your course folder.

1. What are multiple alleles?
2. How many alleles can one organism have for a gene with multiple alleles?
3. Define or explain co-dominance?
4. What is incomplete dominance?
5. How do the phenotypic and genotypic ratios compare for an incomplete dominant trait?

Module 6: Lesson 3 Assignment—Labs

Breeding chickens has never been easier! You will complete a Gizmo on Chicken Genetics and all of the activities indicated in the lab.

3.6.3 page 3

Lesson 3 Lab: Chicken Genetics

Not all genes have one dominant and one recessive allele. Sometimes the presence of any allele leads to some kind of change in phenotype. With flower phenotype, if you have one of each allele, you have a blend and the resulting phenotype is pink. In this simulation you will explore chicken colour. You will conduct various breeding cycles until you determine the mode of inheritance, and until you can answer all of the questions based on co-dominance.

Problem (Purpose)

Manipulate the P1 breeding pair and observe the resulting offspring to determine the mode of inheritance for colour in chickens.

Materials

For this simulation, you will require access to the Internet and a word processing program to record your results.

Procedure

Open the Gizmo on Chicken Genetics. (Put your username/password into the top login box.) In this investigation you will follow the instructions listed in the exploration guide for the part titled “Inheritance of a Co-dominant Trait.”

As you read and follow the instructions, make sure you are able to answer the questions listed for yourself. Some of them will be repeated later in this lab for you to submit to your instructor for assessment.

Observations

The top two spots in the hen house are the P1, or parental generation. Whichever two chickens you place here will breed to create the other five spots you see in the hen house. Your first breeding pair should consist of one red and one white chicken. What kind of offspring result? Does it matter how many times you click “breed”? The next set of parents should be two heterozygous birds (mixed colour for phenotype). What kind of offspring may result from this cross? As asked in the Exploration guide, run this cross until you have at least 100 offspring.

3.6.3 page 4

Module 6—Mendelian Genetics and Inheritance

Read

From his work with peas, Mendel concluded that two kinds of factors control every trait, and that each individual has a pair of these factors; one inherited from the mother, and one from the father. In each case, one factor was dominant to the other. As you have just learned with spotting in cats and four-o'clock flower colour, exceptions to dominance exist. You may also not find it surprising to discover that more than two alleles may affect the same trait.

Multiple allelic traits are described in your textbook on pages 604, 605 and 606. Read these pages carefully before you proceed any further. As you do this reading, consider the adaptive advantages that multiple alleles might provide. Remember that variety contributes to biodiversity, and biodiversity is the key to the survival of species.

Try This

Examine the sample blood type problems on the top of page 606 of your textbook. Notice how they indicate alleles using a capital I as the letter base, then adding a superscript A or B if indicating one of the co-dominant alleles, and using a lower case i with no superscript for the recessive O allele. Complete questions #11, 13 – 15, and 17 on the bottom of page 606 of your textbook. Discuss your work with your instructor. Save your answers to your course folder.

Self-Check

Answer the following questions to check your understanding of the material in this lesson.

1. In short-horned cattle, red is co-dominant with white. The hybrid is called roan. A roan mates with a roan. Use a Punnett Square to determine the expected phenotypes of the offspring.
2. The alleles for hair type show incomplete dominance. One allele (c) is for curly hair. Another allele (s) is for straight hair. The hybrid is wavy.  A wavy haired person marries a curly haired person. Use a Punnett Square to determine the expected phenotypes of their children.
3. A rooster with grey feathers is mated with a hen of the same phenotype. Among their offspring, 15 chicks are grey, 6 are black and 8 are white.
   
   
   1. What is the simplest explanation for the inheritance of these colors in chickens?
   2. What offspring would you expect from the mating of a grey rooster and a black hen?
4. Colour patterns in a species of duck are determined by one gene with three alleles. Alleles H and I are semi-dominant (i.e., incomplete dominance), and allele i is recessive to both. How many phenotypes are possible in a flock of ducks that contains all of the possible combinations of these three alleles?

3.6.3 page 5

Reflect and Connect

By adding knowledge of multiple alleles and incomplete dominance to what you have already learned about genetics, you have greatly expanded your ability to interpret phenotypes and predict inheritance. All this and you are still working only with one gene! When each chromosome has hundreds of genes, and humans have 23 chromosome pairs, think of all the possible variations that exist. Now would be a good time to review your genetics study dictionary and add the new terms from this lesson.

Self-Check

For an excellent self-check, go back to the Arizona biology project website and finish the questions on monohybrid crosses (9–13). Each problem has a tutorial to help, if you have any questions, and also explains the correct answer when given.

Reflect on the Big Picture

Understanding blood types and their inheritance pattern can go a long way when working with family histories, developing pedigrees (charts which trace the inheritance of genetic characteristics through generations), and determining paternity. In biology 20, you learned about the different types of blood and what can happen if a person receives incompatible blood. In this lesson, you will examine the three alleles for blood type and how they account for the four phenotypes possible. Using this information, you can predict possible blood types of future children, study family pedigrees to determine lineage, and even determine if there was a mix up in the hospital!

Lesson Summary

During this lesson you were to focus on the following essential questions:

• What happens when one allele is not completely dominant over another?
• How does having more than two alleles for a gene affect the possible phenotypes for a trait?

In cases where one allele is not completely dominant over another, each allele is somewhat expressed. If the heterozygous phenotype appears to be more of a blend, as with flower colour, this is called intermediate inheritance. Co-dominance is when each allele is fully expressed in different parts, like with black and white hairs in roan horses.

When multiple alleles are present for a trait there will be many possible phenotypes. Each individual still has only two alleles, but there may be many possible combinations for these two alleles in the population as a whole. Each allele set can still be analyzed with the patterns we’ve learned. One allele will either be dominant over the other, or it will be incompletely dominant. With many alleles this may lead to an order of dominance, as seen in rabbits.

Lesson 3.6.4

Lesson 4—Dihybrid Crosses

Get Focused

Working with one gene at a time is a lot like playing catch. It takes a few tosses in the back yard with mom, dad or an older sibling, but after a bit of practice, it becomes second nature. Working with two or more genes is more like juggling. The basic concepts are all the same. All of the inheritance types we have covered still apply, only now you will need to keep your eye on two genes, each with their own alleles. The total movement is trickier, and the process might take a bit more practice.

In this lesson, you will learn how to follow the inheritance of two separate traits at the same time. As you follow two traits at once, you will understand how the movement of alleles for one trait does not effect the movement of alleles for the other trait during the formation of gametes.

In this lesson, the following focusing question will be examined:

• How do scientists track the inheritance of more than one trait at a time?

This lesson will take approximately 100 minutes to complete.

Module 6: Lesson 4 Assignment

You will complete a lab on mouse genetics (two traits) for assessment.

Once you have completed the learning activities in the lesson you can complete the online assignment.

Bio30 3.6.4 online assignment

The other questions and activities in this lesson are not marked by the teacher; however, you should still attempt all of the work offered here. They are designed to help you review important information and build key concepts that may be applied in future lessons.

Here is a tutorial video for this lesson that you can watch if it suits your learning style.  Bio30 tut#3.6.4 Dihybrid Probability.

3.6.4 page 2

Read

Mendel was interested in determining whether the movement of one trait’s alleles affected the movement of another trait’s alleles. To test this out he conducted crosses between plants that were true breeding for two traits. When a cross is carried out to observe two traits at the same time it is called a dihybrid cross. If three traits were being analyzed at once, it would be a trihybrid cross, and so on.

One of the most important discoveries Mendel made when conducting dihybrid crosses was the discovery that the movement of alleles for different genes did not affect each other. This led him to propose his second law: The Law of Independent Assortment. Read about this law, and about how to write out a large, 16 square Punnett square to track dihybrid crosses on page 593 of your text.

Watch and Listen

Consider the following video on Classical Genetics and Dihybrid Crosses (about 15 minutes). Using the navigation bar on the right edge of the video, start watching the section titled “Objectives.” Continue to watch until the end of “Bio Simulation: Mendel’s Dihybrid Cross.” Answer the following questions for your own understanding, and save your work in your course folder.

1. What was the letter assignment used here for Widows peak / Straight hair line, and for Normal thumb / hitch hiker’s thumb?
2. What hypothesis (if/then statement) did the students create to test whether the attachment of ear lobes was a trait controlled by a dominant or a recessive allele?
3. Did they find many people with all three traits recessive?
4. In your own words, state or explain Mendel’s second law, the Law of Independent Assortment.
5. Starting with parents that are true breeding for two independent traits, what will be the resulting phenotypic ratio in the F2 generation?

        ___ dom / dom:         ___ dom / rec:           ___ rec / dom:           ___ rec / rec

6. Does the movement of the alleles for plant height affect the movement of the alleles for flower colour?

Try This

Review again how to create gametes from parents, and then how to build a 16-square Punnett square by examining "Figure 17.10" on page 593 of your text. If you are still unsure about how the gametes fill in the square, search the Internet for dihybrid tutorials or speak with your teacher.

Now answer question 6 on page 598 of your text. Use a Punnett square to find all of the genotypes and phenotypes in part (b). Save your answers to your course folder.

Watch and Listen

 Here is video to review the fundamentals of dihybrid crosses.

Punnett square creation for dihybrids

Module 6: Lesson 4 Assignment—Labs

From your practice in previous lessons, you should be strong in tracking the movement of alleles for one gene, such as plant height. In this lesson, you have been introduced to the independent movement of four alleles; two for each separate gene, such as plant height and seed colour. Now you need some practice to know how this looks in the lab, and to know how specific ratios in offspring help us understand the genotypes of the parents.

You will complete a Gizmo on Mouse Genetics (Two Traits)and all of the activities indicated in the lab. You will be prompted to complete the Module 6: Lesson 4 Assignment as part of the lab.

3.6.4 page 3

Lesson 4 Lab: Mouse Genetics (Two Traits)

Mendel wanted to know if the separation of alleles on one gene had any effect on the separation of alleles on another. To test this, he looked at plants that were pure breeding for two traits at once. He crossed plants that were true breeding for two traits with plants that were true breeding for the opposite forms of the same traits. In conducting and analyzing those crosses, Mendel was able to discover predictable patterns and ratios in the phenotypes of the F1 and F2 offspring.

In this simulation, you will explore mouse coat colour and eye colour as two separate genetic traits. You will conduct various breeding cycles until you understand how each trait separates in the F1 and F2 offspring. You will also determine if the movement of alleles for one trait has any effect on the movement of alleles for the other trait.

Problem (Purpose)

Manipulate the P1 breeding pair and observe the resulting offspring to determine which allele is dominant for each trait, and to see if one trait has an effect on the other.

Materials

For this simulation you will require access to the Internet and a word processing program to record your results.

Procedure

Open the Gizmo on Mouse Genetics.

Locate the “Exploration Guide” and open this document. In this investigation you will follow the instructions listed in the exploration guide for the parts titled

• Patterns of inheritance
• Independent Assortment

As you read and follow the instructions, make sure you are able to answer the questions listed for yourself. Some of them will be repeated later in this lab for you to submit to your instructor.

Observations

Patterns of Inheritance

Follow all of the instructions under this heading. Stop after you have completed Step 4.

3.6.4 page 4

Self-Check

Answer the following questions to check your understanding of the material in this lesson.

1. In pepper plants, green (G) fruit colour is dominant to red (g) fruit colour, and round (R) fruit shape is dominant to square (r) fruit shape. These two genes are located on different chromosomes.
   
   
   1. What gamete types will be produced by a heterozygous green, round plant?
   2. If two such heterozygous plants are crossed, what genotypes and phenotypes will be seen in the offspring, and in what proportions?

2. In watermelons, the genes for green colour and for short shape are dominant over the alleles for striped colour and for long shape. Suppose a plant with long, striped fruit is crossed with a plant that is heterozygous for green colour, and homozygous for short shape. What is the phenotype of their offspring (Show all work)?
3. In humans, a cleft chin is due to a dominant allele (D), while the recessive allele (d) produces no cleft. Most people have free ear lobes due to a dominant allele (E), and a person with attached ear lobes has two recessive alleles (e). If a mother is homozygous for cleft chin and heterozygous for free ear lobes, and the father is heterozygous for both traits, determine the following:
   
   
   1. What is the probability that their baby will have the following?
      
      
      1. A cleft chin and attached ear lobes?
      2. A cleft chin and free ear lobes?
      3. No cleft chin and free ear lobes?
      4. No cleft chin and attached ear lobes?
   2. Draw a Punnett square to support your answer.

4. The allele for black coat colour (B) is dominant over the allele for white coat colour (b) in dogs. The allele for short hair (S) is dominant over the allele for long hair (s). The phenotypes of offspring from several crosses are given below.

Complete the following:

1. What are the genotypes for parents of each of the four crosses (you can’t be sure of cross one)?
2. If the black coat colour and long hair offspring from Cross 3 is crossed with the black and short hair offspring from Cross 1 (assume both parents are BB), what proportion of the offspring will have black, short hair? Is it possible to have offspring with white, long hair from this cross?

Self-Check Answers

1.  
   1. The green round plant will produce GR, Gr, gR, and gr gametes in equal proportion since the genes are unlinked.
   2. This will give 9/16 green round, 3/16 green square, 3/16 red round, and 1/16 red square phenotypes; the genotypes are given in the Punnett square below.
2. Allele assignment:     G = green, g = stripped, S = short, s = long.
   Parents:                      ggss x GgSS
   Gametes:                   [gs] x [GS], [gS]
   Offspring:                   GgSs, ggSs
   Phenotype:                50% green short : 50% striped short
3. Parents:    DDEe             x          DdEe
   Gametes: [DE], [De]       x          [DE], [De], [dE], [de]
   
   
   1. What is the probability that their baby will have the following?
      
      
      1. A cleft chin and attached ear lobes?         1/4
      2. A cleft chin and free ear lobes?                3/4
      3. No cleft chin and free ear lobes?                0
      4. No cleft chin and attached ear lobes?        0
   2. Punnett square supporting the answer:

4. 1. Cross 1:         BBSs  x          BBss               Cross 2:         bbSs   x          bbSs
      Cross 3:         BbSs  x          Bbss               Cross 4;         Bbss   x          Bbss
   2. Offspring with black, short hair:       1/2 or 50%
      Not possible to have white long hair since the only colour allele present is B.

3.6.4 page 5

Reflect and Connect

This lesson has helped you to understand how to track two traits at the same time, while still following all of the inheritance patterns you have already learned. Complete the following Self Check to apply all of the principles that you have been mastering. 

Self-Check

Return to the Arizona biology project website and work through the dihybrid cross problem set. Each problem has a tutorial to help you, should you encounter any problems. These may take a little more time, but are worth the practice. Practice is essential to mastering the concepts and applications in genetics.

Lesson Summary

During this lesson you were to consider the following focusing question:

• How do scientists track the inheritance of more than one trait at a time?

By learning Mendel’s law of independent assortment, and how to build dihybrid Punnett squares, you can now follow the movement of two traits on different chromosomes at once.

Lesson 3.6.5

Lesson 5—Probability

Get Focused

Working with genetics has a lot to do with predicting outcomes. Just like tossing a coin to decide who kicks the ball at a football game, there is always a certain amount of chance in genetic outcomes. Still, the players at the game know that there are only two possible outcomes, and the likelihood of either one is 50%.

By reviewing how probabilities of traits work together, and by learning the product or addition rule, you will be able to more reliably predict how a trait, or traits, should move from generation to generation.

In this lesson, you will learn how to predict the genetic outcome of future generations by examining numbers and ratios. Patterns can give the likelihood of a trait remaining hidden or being expressed.

In this lesson, the following focusing question will be examined:

• How can ratios be used to analyze types of inheritance or to predict the possibility of a trait appearing in the next generation?

This lesson will take approximately 60 minutes to complete.

Module 6: Lesson 5 Assignment

 Once you have completed all of the learning activities for this lesson, you can complete the online assignment.

Bio30 3.6.5 online assignment

The other questions and activities in this lesson are not marked by the teacher; however, you should still attempt all of the work offered here. They are designed to help you review important information and build key concepts that may be applied in future lessons.

3.6.5 page 2

Read

Probabilities are usually expressed as real numbers with values from zero to one. You may also express them as fractions or percentages. A probability of zero means NO CHANCE, while a probability of one means it’s a SURE THING. Anywhere in between, the chance will differ; low values indicate it is unlikely, high values indicate it is likely. There are two general rules when considering probability. They are the rules of addition and product. Deciding when to use which rule depends on whether the probabilities are linked or independent.

Addition Rule

If two outcomes are mutually exclusive (you can have one but not the other), the probability that either will occur is their sum.

Dice Example

• The probability that we will roll a 3 on a single die is 1/6 [6 for the 6 sides, or possibilities]

• The probability that we will roll a 4 is the same (1/6).

• Thus, the probability that we will roll either a 3 or a 4 is 1/6+1/6 = 1/3

Having many exclusive outcomes makes the likelihood, or probability, increase.

Multiplication Rule

If two outcomes are independent (not linked), the probability that both will occur is their product.

Dice Example:

• The probability that we will roll a 6 on a single die is 1/6, and the probability that we will roll a 6 on a second die is the same.

• However, the probability that we will roll two sixes on a pair of dice (at once) is 1/6x1/6 = 1/36.

Having many independent outcomes occur at once makes the likelihood, or probability, decrease.

Example:

Which rules will be applied?

• The multiplication rule will be applied.

How will it be applied?

• Take the probability of the first event, times the second, times the third.

So what is the probability of “Heads - Tails - Tails” in a coin toss?

• (½) x (½) x (½) = 1/8 chance or 0.125 or 12.5%

Watch and Listen

Return again to the video on Classical Genetics and Di-hybrid Crosses (about 10 minutes left). Using the navigation bar on the right edge of the video, start watching the section titled “Bio Bit: Di-hybrid Crosses in Canaries”. Continue viewing until the end the video. Answer the following questions for your own understanding, and save your work in your course folder.

1. What is the probability of rolling a three on one die?

2. What does the sum of all possibilities equal?

3. What is the probability of rolling a six on two different dice at the same time? To figure this out, what “rule” did you need to use?

4. How can you use this rule and two smaller Punnett squares to predict the offspring of a Di-hybrid cross?

5. If you assume that the parents are heterozygous for all three traits in the film, what is the probability of having a child with widow’s peak, hitchhiker’s thumb, and free earlobes?

3.6.5 page 3

Lesson 5 Lab—Calculating Probability

What are the chances of a person winning the Lotto 649 lottery? One chance in ten million? What are the chances of a person being struck by lightning? One chance in two million? If you are more likely to be struck by lightning than winning the lottery, then which should you be more concerned about?

Probability can be defined as a study of the chance that certain events or phenomena will happen. In this lab, you will explore how probabilities with coin tosses can be either linked or not linked. You will then draw connections between the outcomes of coin tosses with the outcomes of genetic crosses.

Problem (Purpose)

The objective of this investigation is to study the probability associated with tossing coins.

Materials

• paper

• a small cup

• pencil

• two coins of the same denomination

• Module 6: Lesson 5 Assignment document that you saved to your computer earlier in this lesson.

Procedure

• Place one coin in the cup. Cover the cup opening with your hand and shake. Then, toss the coin on the table. Repeat ten times. Record the number of heads and the number of tails you got in Table A of your assignment document.

• Using the same procedure, toss one coin fifty times. Record the number of heads and tails in Table B of your assignment document.

• Toss two coins at the same time forty-eight times using the same procedure as before. For each group of eight tosses, record in Table C in your assignment document the number of double heads, one head one tail, and double tails that you get.

• In this exercise, you want to toss three consecutive heads tossing one coin, or, to speed up the process, toss three coins together and attempt to get heads on all three coins on the same toss. Before you start, predict what your chances are of getting heads on all three coins. Now try it, keeping count of the number of attempts made until you get the first set of three heads. Record the number of tosses it took in the Table D of your assignment document.  Try it again and record the number of tosses in the assignment document.

If you have ever had to guess a coin toss, our experience has probably taught you to appreciate the randomness of chance. In general, the more often an event occurs, the closer the actual frequency comes to the predicted frequency. Sometimes you think you know the probability of an event occurring, but to your dismay it doesn’t happen this way! You later discover that you were lacking some key information. Consider the case in the next lesson.

3.6.5 page 4

Self-Check

Try out these questions to see if you have mastered the use of probabilities.

1. The ability to taste the chemical PTC is determined by a single gene in humans, with the ability to taste PTC indicated by the dominant allele T, and the inability to taste PTC by the recessive allele t. Suppose two heterozygous tasters (Tt) have a large family. 

   1. Predict the proportion of their children who will be tasters and non-tasters. Use a Punnett square to illustrate how you made this prediction.

   2. What is the likelihood that their first child will be a taster? What is the likelihood that their fourth child will be a taster?

   3. What is the likelihood that the first three children of this couple will be non-tasters?

2. A husband and wife are both heterozygous for a recessive gene, c, for albinism. They were informed that the twins they are expecting are dizygotic, a boy and a girl.

   1. Draw a Punnett square of this cross.

   2. What are the chances that one child will be albino?

   3. What are the chances that both children will be normal?

   4. What are the chances that both babies will have the same phenotype for skin pigmentation?

3.6.5 page 5

Reflect and Connect

By conducting the lab on coin tosses you should have been able to make the connection between probabilities in genetics and everyday events. It takes some practice, but probabilities can help solve genetics problems faster than writing out complete Punnett squares. To practice your skills, complete the following questions and check your answers. If you are encountering any difficulty, consult with your instructor.

Diploma Connection

Answer the following questions from a previous Biology 30 Diploma Exam.

Numerical Response

1. A dominant allele, XE, carried on the X chromosome, causes the formation of faulty tooth enamel, resulting in either very thin or very hard enamel. A woman heterozygous for faulty tooth enamel marries a man with normal tooth enamel. What is the probability that their first child will be a boy with normal tooth enamel?

Answer: _____________

Numerical Response

2. In sheep, white wool is a dominant trait, and black wool is a recessive trait. In a herd of 500 sheep, 20 sheep have black wool. If two heterozygous sheep mated, what would be the probability of them having a white lamb?

Answer: _____________

Use the following information to answer the next question.

Numerical Response

3. These parents, who are unaffected by cystic fibrosis, are planning to have another child. What is the percentage probability that their next child will be affected by cystic fibrosis? (Record your answer as a whole number.)

Answer:          _____________ %

Use the following information to answer the next question.

Numerical Response

4. A man, heterozygous for Marfan syndrome, and a homozygous recessive woman have a child. What is the probability that the child will be affected by Marfan syndrome? (Record your answer as a value from 0 to 1, rounded to two decimal places.)

Answer:          _____________

Use the following information to answer the next question.

5. What is the probability that their daughter has inherited the mutant BRCA1 gene?
   
   
   1. 75%
   2. 50%
   3. 25%
   4. 0%

Lesson Summary

During this lesson, you were to consider the following focusing question:

• How can ratios be used to analyze types of inheritance or to predict the possibility of a trait appearing in the next generation?

Through the practice questions and the coin toss lab you have been given the opportunity to practice doing just that. By adding or multiplying the probabilities of individual traits, you have been able to predict the possible phenotypic outcomes of the next generation for two or three different traits. This can help answer genetic problems much more quickly than drawing out large Punnett squares.

Lesson 3.6.6

Get Focused

Genetics, it seems, does not always play equally with each gender. Have you ever noticed that there are quite a few more balding men than balding women? Perhaps you know of someone who is colourblind. If you do, it is far more likely that they are male than female. Each of these examples indicates that there is more going on than independent assortment. There appears to be a link between the appearance of certain traits and gender.

In this lesson, you will begin to explore inheritance patterns that do not follow Mendel’s laws. You will see how some traits occur more frequently in one gender than the other, and are said to be linked.

In this lesson, the following focusing questions will be examined:

• Why do some traits appear more frequently in one gender rather than the other?

• How did Thomas Hunt Morgan’s work create experimental support for the chromosomal theory of inheritance?

This lesson will take approximately 80 minutes to complete.

Module 6: Lesson 6 Assignment

Once you have completed all of the learning activities in the lesson, you can complete the online assignment.

Bio30 3.6.6 online assignment

The other questions and activities in this lesson are not marked by the teacher; however, you should still attempt all of the work offered here. They are designed to help you review important information and build key concepts that may be applied in future lessons.

Here is a tutorial video for this lesson that you can watch if it suits your learning style.  Bio30 tut#3.6.6 Gene Interactions

3.6.6 page 2

Explore

Read

Chromosome Theory of Inheritance

Before considering how certain traits are linked to gender, we need to put together two ideas that you already know of. First let’s review Mendel’s laws. His first law explains how parents have two alleles for a trait, and that these alleles separate during the formation of gametes. As a result, gametes have only one allele for each trait. His second law explains how two or more allele pairs segregate independently of one another into gametes. As a result, the inheritance of one characteristic can have little relationship to the inheritance of a different characteristic.

Now, try to think back to the previous module on cellular division and meiosis. When diploid organisms go through meiosis, homologous pairs of chromosomes are separated during the formation of gametes. Therefore, for each pair of gametes produced, each of the two gametes has only one homologous chromosome. In meiosis I, during metaphase I, each pair of homologous chromosomes lines up on the equator and then separates independently of every other pair. Can you see the similarities between the description of Mendel’s laws and the movement of chromosomes in meiosis? A fellow named Walter Sutton noticed these similarities and proposed that Mendel’s factors, now called genes, were found on chromosomes. He proposed a theory called the Chromosomal Theory of Inheritance. Read about genes and chromosomes in your textbook on pages 596–597.

Sex-Linked Inheritance

Like most theories, the chromosomal theory of inheritance was not widely accepted in the beginning. It took the work of Thomas Hunt Morgan to finally add some scientific proof of its validity. Morgan was actually trying to disprove the theory, but when his experimental evidence supported it, he changed his position. While working with Drosophila, Morgan and his team noticed that when crossing red eye dominant flies with white eye recessive flies he obtained the expected 3 red : 1 white ratio in the F2. However, the white was not equally distributed among males and females. Instead, all of the white eyed flies were male. None of them were female. This observation led him to propose the hypothesis that the gene for eye colour in Drosophila must occur on the X chromosome. Read the first section on Thomas Hunt Morgan on page 599 of you text. Then, skip the sections on linked genes, chromosome maps, and crossing over, and continue reading about Sex-linked inheritance on pages 601–603.

Watch and Listen

Consider the following video on Studying Sex-Linked Inheritance in fruit flies

Please watch the following sections:

• Examining Fruit Flies

•  Inheritance of White Eye Colour

• Patterned Sex-Linked Inheritance

1. Why do many geneticists study fruit flies?
2. What tells the students that eye colour in fruit flies is not autosomal, but rather linked to gender?
3. What chromosome actually carries the allele for eye colour in fruit flies?
4. What happens in males with the alleles that occur on X chromosomes?
5. Can males pass on X-linked traits to their sons?
6. What is the term used to describe the genes located on the X chromosome in males

3.6.6 page 3

Reflect and Connect

By recognizing that genes are located on chromosomes, you can now go far beyond what Mendel was able to do by crossing peas and analyzing outcomes. You should now be able to explain X-linked inheritance, since you know that females have two X chromosomes, and that males have only one. You should also be able to understand how non-disjunction will have dramatic results on offspring by adding or removing thousands of alleles. It has been a few lessons since you’ve looked at your genetic study dictionary. Bring that out again, and add any terms we’ve been using in this lesson that are not in there yet. You may also wish to add entries or flashcards that show patterns of inheritance on one side, with the explanation on the other. To test your understanding of this lesson’s connections to the aspects of genetics that you have already learned about, complete the following questions. If you are having difficulty, consult with your instructor.

Diploma Connection

Answer the following questions from a previous Biology 30 Diploma Exam.

In humans, the allele for normal blood clotting (H) is dominant to the allele for hemophilia . The trait is X-linked.

1. A female hemophiliac marries a man who is not a hemophiliac. The row that indicates the probability of this couple having a child that is a hemophiliac, and indicates the sex that the child would be is
   
   

   Row	Probability	Sex of Affected Child
   A.	0.25	male
   B.	0.25	either female or male
   C.	0.50	male
   D.	0.50	either male or female

   
   Answer: ___________
2. A woman who is not a hemophiliac has a father who is a hemophiliac. If this woman marries a man who is a hemophiliac, what is the probability of them having a hemophiliac son?
   
   Answer: ___________

Use the following information to answer the next question.

A recessive allele causes Drosophila to have white eyes instead of wild-type eyes. This eye colour gene is known to be X-linked. In a cross between homozygous wild-type females and white-eyed males, all F1 progeny have wild-type eyes.

3. What ratio of wild-type to white-eyed progeny can be expected in each sex if F1 females are crossed to males of the same genotype as their father?
   
   
   1. Males – 1:0; females – 1:0
   2. Males – 1:1; females – 1:0
   3. Males – 0:1; females – 1:1
   4. Males – 1:1; females – 1:1

Answer: ___________

Use the following information to answer the next question.

4. To determine whether this is an X chromosome or an autosome, a researcher would have to determine whether these traits are
   
   
   1. recessive
   2. dominant
   3. passed from male parents to their male offspring
   4. passed from female parents to their male offspring
   
   Answer: ___________

Use the following information to answer the next question.

Scientists have identified a genetic condition that apparently makes some men prone to impulsive, violent behaviour. A pedigree was drawn highlighting the violent members of a particular family. It appeared, from the pedigree, that men who displayed this violent behaviour inherited this condition from their mothers, not their fathers. Further evidence showed that this was the mode of inheritance.

—from Richardson, 1993

5. The inheritance pattern described indicates that this condition is
   
   
   1. X-linked
   2. Y-linked
   3. autosomal
   4. codominant
   
   Answer: ___________

Self-Check

For a very good self-check, go back to the Arizona biology project website and work on the Sex-linked Inheritance Problem set (1–10). As always, each problem has a tutorial to help you if you run into any problems with the questions. Also, the correct answer is explained when you reach it.

Lesson Summary

During this lesson you were to examine the following focusing questions:

• Why do some traits appear more frequently in one gender rather than the other?
• How did Thomas Hunt Morgan’s work create experimental support for the chromosomal theory of inheritance?

Genes occur on chromosomes. This is true for all chromosomes, including the X chromosome. However, the Y chromosome has few genes. Since males receive only one X chromosome, they will have a different rate of inheritance than females for all traits whose alleles are located on the X chromosome. Most genetic diseases are recessive traits. So, for any recessive traits or diseases appearing on the X chromosome, males will have a higher incidence of that trait or disease than will females. This is because males always express whichever allele they receive on the X chromosome. Therefore, males have a fifty : fifty chance of expressing the trait. Females often have at least one normal, dominant allele to cover up the disease, as in the homozygous dominant and in the heterozygous condition. To express the recessive X-linked trait, a female must be homozygous recessive.

Thomas Hunt Morgan and his team worked with fruit flies to try to disprove the chromosomal theory of inheritance. However, his work proved to generate experimental evidence that actually supported the theory. This evidence indicated that genes were in fact located on chromosomes. For this work he received the Nobel Prize in 1933.

Lesson 3.6.7

Lesson 7—Genes and the Environment

Get Focused

Nature verses nurture. Have you heard the ongoing debate over which is the strongest influence on a person’s life? While this debate is more focused on innate qualities versus personal experiences, it has relevance in genetics too. Our environment can significantly influence our genes. Sun exposure triggers all kinds of genes to be expressed in plants and animals. Exposure to water can change the development of leaves in the same plants. Changes in temperature cause the expression of dark pigment in some rabbits and in Siamese cats. These are very specific examples, but just how much the environment affects gene expression is open for more discussion.

In this lesson, you will examine the effect the environment may have on the expression of genes.

In this lesson, the following focusing question will be examined:

• How does the environment affect the expression of genes?

This lesson will take approximately 60 minutes to complete.

Module 6: Lesson 7 Assignment

There is no assignment for this lesson.

The other questions and activities in this lesson are not marked by the teacher; however, you should still attempt all of the work offered here. They are designed to help you review important information and build key concepts that may be applied in future lessons.

Here is a tutorial video for this lesson that you can watch if it suits your learning style.  Bio30 3.6.7 Gene Interactions

3.6.7 page 2

Read

To set the stage, read the short section in your text on Genes and the Environment on page 609.

Watch and Listen

Watch a short segment from the video on Alternate Patterns of Inheritance: the Potential for Diversity (about 2 minutes). Watch the following sections:

• Bio Break: Environmental Influences
• Bio Discovery: Environmental Influence

Answer the following questions for your own understanding and save your work in your course folder.

1. Is height in humans determined only by our genes?
2. Are our interests genetic or environmental?
3. How does temperature affect coat colour in rabbits?

Module 6: Lesson 7 Assignment—Labs

Can eating sweets or salty foods determine if a pregnant couple will have a boy or a girl? Despite some persistent folk tales, there is nothing a person can do while pregnant that will influence the gender of their child. However, this is not the case with other species. In this exploration, you will determine if a change in temperature will have an effect on the gender of hatching chickens or geckos. By doing so, you will see how environment can indeed affect the expression of genes already present in the developing embryos.

You will complete a gizmo on the effect of temperature on gender and all related activities. You will be prompted to complete your Module 6: Lesson 7 Assignment as part of the lab.

3.6.7 page 3

Reflect and Connect

The incredible effect of temperature on the gender of Gecko hatchings is experimental evidence that genes are affected by the environment. Apply your understanding of the concepts of this lesson to the following questions.

Diploma Connection

Answer the following questions from a previous Biology 30 Diploma Exam.

Use the following information to answer the next question.

1. If scientists are successful in significantly reducing or eliminating malaria, the best prediction for what will happen to the allele for sickle cell anemia in the population is that it will
   
   
   1. not be affected by the elimination of malaria
   2. increase as its selective advantage is increased
   3. be reduced as its selective advantage is decreased
   4. quickly disappear as its selective advantage is increased

Use the following information to answer the next question.

2. The fact that exposure to sunlight increases melanin production in many humans and produces a tan demonstrates that
   
   
   1. some people have mutations that prevent melanin production
   2. the expression of some genes is influenced by the environment
   3. the environment causes mutations that increase the chance of survival
   4. the environment causes mutations that have no effect on the chance of survival

Use the following information to answer the next question.

3. Which of the following conclusions can be drawn from all of the information provided on sickle cell anemia?
   
   
   1. The sickle cell gene will eventually disappear because of its interaction with malaria.
   2. Malaria causes heterozygous individuals to be less fertile than homozygous individuals.
   3. In Africa, sickle cell anemia will disappear since it is lethal in the homozygous condition.
   4. In Africa, carriers for sickle cell anemia have an advantage over homozygous individuals

      1. Lesson Summary

          

         During this lesson, you were to explore the following focusing question:

         • How does the environment affect the expression of genes?

         Through your research for the discussion post, and from your exploration of temperature and gecko hatchings, you should see that there can be a strong and dynamic influence by the environment on gene expression. This influence accounts for some of the variance in traits like height. Whether this environmental effect on the expression of genes is stronger than the very inheritance of those genes is still up for debate.

Lesson 3.6.8

Lesson 8—Polygenetic Traits

Get Focused

On the top of a chicken’s head is a fleshy growth known as its comb. There are four possible phenotypes for chicken combs; rose, pea, walnut, and single. Up until this lesson, if you were presented with this information you would need to suspect multiple alleles were responsible for this trait. However, a walnut chicken can be crossed with another walnut chicken and their offspring can display all four of the possible phenotypes. That would just not be possible with any amount of alleles if this trait was explained by a single gene. This type of inheritance could only be possible if more than one gene was acting to create the same trait!

In this lesson, you will study traits that are controlled by many genes. You will recognize inheritance patterns that show gradual changes in phenotypes, and you will understand that the expression of one gene can turn the expression of another on or off.

In this lesson, the following focusing question will be examined:

• How might multiple genes combine to form a single trait?

This lesson will take approximately 60 minutes to complete.

Module 6: Lesson 8 Assignment

Once you have completed all of the learning activities for this lesson, complete the online assignment.

Bio30 3.6.8 online assignment

The other questions and activities in this lesson are not marked by the teacher; however, you should still attempt all of the work offered here. They are designed to help you review important information and build key concepts that may be applied in future lessons.

3.6.8 page 2

Read

Many traits are actually regulated by more than one gene. Skin colour, eye colour, and height are just a few examples seen in humans. For each of these traits many genes will interact to form the final phenotype. To make things a bit easier to understand, we will focus on traits that result from the interaction of only two genes. There are two main means of causing polygenetic traits: complementary interaction and suppression epistasis. An epistatic gene is a gene that interferes with the expression of another gene.

Complementary Interaction

The example of chicken combs from the introduction follows this type of interaction. In this case, two genes combine to form a phenotype that neither is capable of producing itself alone. One of the genes, the Rose gene, has two alleles; an “R” for a rose comb that is dominant over an “r” allele that leads to a single comb. The other gene, the Pea gene, also has two alleles; a “P” for a pea comb that is dominant over a “p” allele that will also lead to a single comb. Remembering that a chicken will have both of these genes at the same time, here are the possible genotypes for the given phenotypes so far.

• Rose comb:   Rrpp or RRpp
• Pea comb:    rrPp or rrPP
• Single comb: rrpp

The forth phenotype is the walnut comb. This results from the presence of both dominant alleles in the two different genes. The possible genotypes for this are

• Walnut comb: RRPP, RrPP, RRPp or RrPp

When analyzing polygenetic traits, the movement of alleles follows the same patterns as in Di-hybrid crosses, however, the resulting genotypes must be interpreted for only one trait instead of two. For example, if a true breeding Rose chicken (RRpp) was crossed with a true breeding Pea chicken (rrPP), the F1 would be all walnut (RrPp). Continuing on to the F2 there would be a 9 Walnut : 3 Rose : 3 Pea : 1 single comb phenotypic ratio. This looks just like Mendel’s work, until you remember that those ratios are for four different phenotypes of one trait only.

Supression Epistasis

This type of gene interaction takes place when one gene masks the expression of another gene. A good common example is coat colour in mice. Here, one gene determines if pigment is created at all, while another gene determines the type of pigment, like black or brown. In our example, the gene that controls the creation of pigment has two alleles. The allele to produce pigment “C” is dominant over the allele that will lead to no pigment, “c”. The other gene that controls the colour of the pigment also has two alleles. “B” is dominant and produces a black pigment, while “b” is recessive and will lead to brown pigment. Here are the possible phenotypes and their genotypes for this trait.

• Black: BBCC, BbCC, BBCc, BbCc
• Brown: bbCC, bbCc
• White: BBcc, Bbcc, bbcc

When trying to determine phenotype in the case of epistasis, it is often helpful to consider a flow chart like the one below.

For an example cross, start with a Black mouse (BBCC) and a White mouse (bbcc). The F1 will all be Black (BbCc). Continuing on to the F2, there will be 9 Black: 3 Brown: 4 White mice. This is an unusual ratio and not the typical 9:3:3:1 you might have been expecting, but it is characteristic for epistasis.

Continuous Traits

Polygenetic traits can involve the interaction of more than just two genes. These would be too complex for us to predict and analyze, but in a general sense they are not too difficult to understand. Basically, the more genes there are involved in creating a single trait, the greater the variety of possible phenotypes. Read about polygenetic traits and continuous phenotypes in your text on pages 605-607.

Watch and Listen

Let’s finish the rest of the video on Alternate Patterns of Inheritance: the Potential for Diversity (about 10 minutes). Watch the following sections:

• Bio Quest: Rabbit Breeding
• Bio Discovery: Other Inheritance Patterns
• Bio Review: Patterns of Inheritance

Answer the following questions for your own understanding and save the results in your course folder.

1. How many phenotypes are there for rabbit fur colouration?
2. How many genes are involved determining rabbit fur colours?
3. How many genes are involved in determining human skin colour? What else affects human skin colour?
4. What is the phenotypic ratio of purple to white flowers in the case of epistasis.
5. Define or explain the following patterns of inheritance:
   
   
   1. incomplete dominance
   2. multiple alleles
   3. pleiotropy
   4. epistasis
   5. codominance
   6. polygenic inheritance
   7. the effect of the environment (Is this really a pattern of inheritance?)

Self-Check

Work through the following problems to solidify your understanding of polygenetic inheritance.

1. In chickens, most birds do not have feathers on their legs. This phenotype is the result of two genes interacting and having only recessive alleles for both genes. The presence of a dominant allele for either gene or for both genes causes feathers. What is the feathered leg : unfeathered leg ratio in the offspring of chickens that are heterozygous for both genes?
   
   
   1. 9:7
   2. 12:4
   3. 13:3
   4. 15:1
2. In corn plants, a dominant allele (I) inhibits kernel color, while the recessive allele (i) permits color when homozygous. At a different locus, the dominant gene P causes purple kernel color, while the homozygous recessive genotype pp causes red kernels. If plants that are heterozygous at both loci are crossed, what will be the phenotypic ratio of the F1 generation?

3.6.8 page 3

Reflect and Connect

Review your genetic dictionary and test yourself to see how quickly you can give definitions or terms. Be sure to add any new terms we’ve used since the last time you reviewed your dictionary. Apply your understanding of this lesson by completing the following questions and submitting your work to your instructor.

Module 6: Lesson 8 Assignment

Review Question on Breeding Corn

Retrieve your copy of Module 6: Lesson 8 Assignment that you saved to your computer earlier in this lesson. Complete the assignment. Save your completed assignment in your course folder. You will receive instructions later in this lesson on when to submit your assignment to your teacher.

Diploma Connection

Answer the following questions from a previous Biology 30 Diploma Exam.

Feather colour in parakeets is controlled by two genes. For one pigment gene, the B allele produces blue colour, and the b allele does not produce any colour at all. For the other pigment gene, the Y allele produces yellow colour, and the y allele does not produce any colour at all. Any genotype containing at least one B allele and one Y allele will produce a green parakeet.

1. Which of the following parental genotypes could produce offspring displaying all four different colour patterns?
   
   
   1. BBYy   BbYy
   2. BbYY   Bbyy
   3. bbYY   bbyy
   4. Bbyy    bbYy
2. What is the probability of obtaining a blue parakeet when two green heterozygous parakeets are crossed?
   
   
   1. 0
   2. 3/16
   3. 1/4
   4. 9/16

Use the following information to answer the next questions.

Two different genes control the expression of kernel colour in Mexican black corn: a black pigment gene (B), and dotted pigment gene (D). Gene B influences the expression of gene D. The dotted phenotype appears only when gene B is in the homozygous recessive state. A colourless variation occurs when both genes are homozygous recessive.

After pure-breeding black-pigmented plants were crossed with colourless plants, all of the offspring were black-pigmented.

—from Grifiths et al., 1993

3. The genotypes of the parents of these F1 offspring could be
   
   
   1. BBDD bbdd
   2. BbDD bbdd
   3. Bbdd bbDD
   4. bbDD BBdd
4. Plants of the F1 generation are suspected of being heterozygous for both genes. A test cross of colourless plants with the heterozygote plants should produce a phenotypic ratio in the offspring of
   
   
   1. 1:0
   2. 3:1
   3. 2:1:1
   4. 1:1:1:1

Use the following information to answer the next question.

In Labrador retriever dogs, two alleles (B and b) determine whether coat colour will be black (B) or brown (b). Black coat colour is dominant. A second pair of alleles, E and e, are on a separate chromosome from B and b. The homozygous recessive condition, ee, prevents the expression of either allele B or b, and produces a dog with a yellow-coloured coat. Some examples of genotypes and phenotypes for Labrador retrievers are shown below.

                                                Genotype                   Phenotype
                                                BBEe                          black
                                                bbEe                           brown
                                                Bbee                           yellow

Numerical Response

5. Two dogs, each with the genotype BbEe, were crossed. What is the percentage probability that their offspring would have yellow coat colour? (Record your answer as a whole number percentage)

Going Beyond

Try out this question to see if you can build on your understanding of this lesson on gene interaction.

1. In humans, there is a dominant allele that causes Vitiligo, where small-unpigmented spots appear on the body. Also, there is a recessive allele for another gene that causes albinism, which causes the entire body to be unpigmented. Since there is no pigment in albinos, Vitiligo cannot be seen in albinos
   
   A man with vitiligo had an albino mother and normal father. If the man has a child by a phenotypically normal skinned woman who had an albino father, what is the probability of having a phenotypically normal child?
   
   
   1. 0
   2. 1/8
   3. 3/8
   4. 5/8

Lesson Summary

During this lesson you were to examine the following focusing question:

• How might multiple genes combine to form a single trait?

Multiple genes can contribute to the expression of only one trait. Two genes may combine to form a new phenotype that neither can produce on their own. One gene may also affect or control the expression of another gene by regulating a factor that is required by the other gene, such as pigment for hair cells. Many continuous phenotypes such as corn length or bean mass can be explained by each dominant allele of a gene collection being a greater contributor to the total. In each of these examples, more than one gene is combining to give rise to a single trait that can be observed.

Lesson 3.6.9

Get Focused

Sometimes you can find what you are looking for by finding something else that should be in a similar location. Early stud finders worked this way. About 20 years ago, if you wanted to find a 2 × 4 stud in your wall, you may have used a floating magnet held close to the wall. The idea was the magnet would be attracted to the nails in the stud and move towards the nails when you were directly over a stud.

After discovering that genes occurred on chromosomes, scientists learned how to map the relative distances between these genes. This can be tremendously helpful for locating genes of interest, such as genes that cause disease. When scientists already know where to find a more common gene on the same chromosome, these “genes of interest” can be more quickly and easily located.

In this lesson, you will learn how genes that are found on the same chromosome tend to move together and are said to be linked. Using your understanding of crossing-over from meiosis, you will learn how this allows scientists to map the relative locations of genes on the same chromosome.

In this lesson, the following focusing questions will be examined:

• How does crossing-over in chromosomes relate to finding the locations of genes on chromosomes?

• What is the importance of knowing where genes are located on a chromosome?

This lesson will take approximately 80 minutes to complete.

Module 6: Lesson 9 Assignment

You will complete a lab on mapping chromosomes and participate in a discussion on the importance of gene mapping. After you have complete the lesson, you can complete the online assignment.

Bio30 3.6.9. online assignment

The other questions and activities in this lesson are not marked by the teacher; however, you should still attempt all of the work offered here. They are designed to help you review important information and build key concepts that may be applied in future lessons.

Here is a tutorial video for this lesson that you can watch if it suits your learning style.  Bio30 tut#3.6.9 Gene Mapping

3.6.9 page 2

Read

Recall from our lesson on sex linkage that Thomas Hunt Morgan provided experimental evidence that genes occur on chromosomes. This discovery immediately creates a new idea from Mendel’s laws; the idea that traits could tend to move together if they were on the same chromosome.

Mendel did not find this with any of his seven traits. For Mendel’s work, each trait had no relation to another. Each assorted independently. It turns out that each of his traits were found on different chromosomes, so we would expect them to move independently.

Many traits in organisms have now been found to in fact be coded for on the same chromosome. These genes coding for such traits do tend to move together, and are thus called “linked genes”. When first considering linked genes, you may think that these genes always move together, however that is not the case. Even though they are on the same chromosome, there is a process that can exchange pieces of homologous chromosomes during meiosis. You may recall from our lessons on meiosis that this process is called crossing over. The farther apart two genes are on a chromosome, the greater the number of cross over events that will occur between them, and it is less likely that the two traits will move together. The number of crossover events directly relates to distance on a chromosome. Read about linked genes, crossing over and chromosome mapping on pages 599 – 601 of your text.

Watch and Listen

Consider the following video of a lecture in genetics at MIT.

1. How is the phenotypic ratio of the cross GgRr × ggrr different for Independent Assortment than for linked genes (Chromosomal theory)?
2. What is meant by “parental types” of chromosomes?
3. What is meant by “non-parental types” of chromosomes?
4. How does recombination frequency relate to map distance

Self-Check

Answer the following questions to check your understanding of the material covered up to this point.

1. If there were 50 recombination phenotypes in 250 offspring, what is the map distance between the linked alleles?

2. A three-point test cross is performed to identify the locus of each of three alleles in relation to one another. The results were as follows:

   • AC recombinations = 225
   • BC recombinations = 165
   • AB recombinations = 60
   • Parental linkages = 550
   • Total offspring = 1000

   Show the positions and map the distances apart for each allele (A, B, and C) on a chromosome. Calculate the map units, then draw the chromosome.

3.6.9 page 3

Reflect and Connect

By analyzing linked-gene crosses for recombinant phenotypes, and by calculating recombinant frequencies, you can create accurate gene maps for traits. This allows for a much more clear understanding of how or why certain traits tend to move together while others may not, even if found on the same chromosome.

Discuss

The Human Genome Project was one of the largest genetic projects ever completed. It involved the participation of public universities and private companies from around the world, and took over 13 years to complete. Now that it is complete, scientists have a relative map of all human genes found on all chromosomes.

However, the project was not without controversy. In order to encourage private companies to take part, these companies were allowed to patent certain tests that can locate specific genes in people; genes that may predict if a person is going to develop cancer or not. As a result, if a person is at risk for developing cancer due to family histories, hospitals need to pay these companies in order to be granted the right to conduct these tests. In addition, tests for the presence of certain genes may also provide information about other genes that were not originally considered. This kind of information may be very dangerous if the information became available to insurance companies, or to a person’s place of employment.

Diploma Connection

Answer the following questions from a previous Biology 30 Diploma Exam.

1. During meiosis, which of the following pairs of genes has the greatest chance of being separated by crossing over?
   
   
   1. (m) and (d)
   2. (ne) and (p)
   3. (m) and (lc)
   4. (p) and (o)

Use the following additional information to answer the next question.

2. The cross-over frequency between genes O and S is
   
   
   1. 6%
   2. 29%
   3. 31%
   4. 97%

Use the following information to answer the next question.

Numerical Response

3. On human chromosome 6, the order of the genes numbered above is ___, ___, ___ and ___.
4. What is the approximate cross-over frequency between the diabetes mellitus gene and the ragweed sensitivity gene?
   
   
   1. 1.5%
   2. 10.5%
   3. 15.0%
   4. 22.5%

Use the following information to answer the next question.

Gregor Mendel examined the inheritance of two traits in pea plants: seed coat texture and colour. Seed coat texture can be represented as S–smooth and s–wrinkled, and seed coat colour can be represented as Y–yellow and y–green. SSYY plants were crossed with ssyy plants to yield F1 pea seeds that were all smooth and all yellow. By crossing plants grown from these F1 seeds, Mendel obtained four different phenotypes of F2 seeds:

• smooth, green seeds

• wrinkled, green seeds

• smooth, yellow seeds

• wrinkled, yellow seeds

5. If the traits for seed coat texture and seed coat colour had been located close together on the same chromosome, Mendel might not have conceptualized
   
   
   1. gene pairs
   2. dominance
   3. the Law of Segregation
   4. the Law of Independent Assortment

Going Beyond

For a challenge, go back to the Arizona biology project website and work through the second set of sex-linked inheritance problems. In this set, each question builds on the next, and the last question requires an understanding of linked genes.

Lesson Summary

During this lesson you were to examine the following focusing questions:

• How does crossing-over in chromosomes relate to finding the locations of genes on chromosomes?

• What is the importance of knowing where genes are located on a chromosome?

Genes on the same chromosome tend to be inherited together. If they are not, it is a result of a crossover event during meiosis. The farther apart the genes are on a chromosome, the more likely a crossover event will occur, and the higher the recombinant frequencies are in the offspring.

By understanding where genes are located on chromosomes geneticists can better predict the inheritance of those genes. Scientists can also design tests that detect the presence of those genes, or genes known to be nearby, just like the old stud finders could find wooden studs in walls by detecting the nails in them.

Lesson 3.6.10

Lesson 10—Plant, Animal and Human Genetics

Get Focused

Family histories are very interesting to trace. Simply tracing your lineage back a few generations may reveal that your family has owned land in a far-away country, or that you are related to someone in your home town. While a hidden genetic disorder may not be what you are hoping to uncover, a good descriptive family tree may indicate that as well.

By creating and analyzing pedigrees, you will be able to track the inheritance of rare genetic diseases through families.

In this lesson, the following focusing question will be examined:

• What technologies exist to help us explain and predict the inheritance of traits in breeding programs or family histories?

This lesson will take approximately 80 minutes to complete. This may take longer due to the lab that involves interviewing family members.

Module 6: Lesson 10 Assignment

There is no assignment for this lesson.

Here is a tutorial video for this lesson that you can watch if it suits your learning style

3.6.10 page 2

Read

A pedigree is a very useful tool for tracking the inheritance of traits. It is similar to a Punnett square, but instead of showing all of the possibilities, it only shows the actual parents and children. A pedigree is like a flowchart illustrating many generations of people and their relationship to one another. By using the proper symbols, you can also indicate the presence or absence of traits, and in doing so, create a pattern that can be analyzed. While all of the patterns of inheritance that we have studied can be analyzed with pedigrees, three primary types will be studied in this lesson: autosomal dominant, autosomal recessive, and sex-linked traits. Read about tracing human genetics and creating pedigrees in your text on pages 611 – 615. Be sure to take good note of all of the possible symbols for pedigrees, which are detailed at the top of page 612.

Remember that autosomal chromosomes are all of the chromosomes that are not sex chromosomes. So anything that is not an X or a Y chromosome is an autosome. A dominant trait will show up in a pedigree by having an affected individual in every generation. This type of vertical pattern should be very clear. In addition, and autosomal trait will not show any preference to gender. There should be roughly the same number of affected males as females.

A recessive trait will show up in pedigrees when neither parent expresses the trait, such as an inheritable disease, however one or more of their children do. If the pedigree is long enough it may also indicate the disease showing up few generations later. Again, since this is autosomal, male and female offspring should be equally represented in the affected individuals.

There are a few distinguishing features of sex-linked inheritance. The first is a gender bias. For X-linked recessive traits, males will be more commonly affected than females. Remember that males give their X chromosomes to their daughters, not their sons. So on an X-linked recessive pedigree there is often an affected male who appears to have no affected offspring. In such a case, one or more of his daughters will have sons affected with the disease.

From your reading in the text, or from the summary presented here, you should answer the following questions for your own understanding and save your work in your course folder.

1. Distinguish between the significance of roman numerals and Arabic numerals when used in a pedigree.
2. What is autosomal inheritance?
3. How do pedigrees for autosomal recessive and X-linked recessive traits differ?
4. Can a female express an X-linked trait like hemophilia? Explain.

Practice Problems

Examine the sample pedigree problem on the bottom of page 614 of your textbook. Notice how they use roman numerals for generations and Arabic numerals for individuals. Also, try to follow the logic used to deduce carriers for the trait based on affected offspring and/or parents. Now, complete the four practice problems on the top of page 615. Save your work to your course folder.

Module 6: Lesson 10 Assignment—Lab: Creating a Real Pedigree

Creating pedigrees is very helpful in determining inheritance patterns in families. Here is a chance for you to determine the inheritance pattern of a single trait in your own family, or a family willing to participate in your investigation.

Retrieve your copy of Module 6: Lesson 10 Assignment that you saved to your computer earlier in this lesson. Complete the assignment. Save your completed assignment in your course folder. You will receive instructions later in this lesson on when to submit your assignment to your teacher.

3.6.10 page 3

Reflect and Connect

Pedigrees are a very clear way to display the inheritance of a trait within human populations. They can also be used to predict the likelihood of future offspring expressing a particular trait. Now, take out your genetic dictionary for the final time. Spend some time reviewing your terms. Add new entries on the material regarding pedigrees. Save the completed copy to your course folder, and review it when you are preparing for your Diploma exam.

Apply the concepts that you have studied by answering the following Diploma-style questions.

Diploma Connection

Answer the following questions from a previous Biology 30 Diploma Exam.

1. Describe one piece of evidence obtained from the analysis of a pedigree chart that could be used to determine whether the mode of inheritance of a human genetic disorder is X-linked or autosomal and one piece of evidence that could be used to determine whether it is recessive or dominant. Construct a pedigree of four generations that clearly illustrates one of the two types of inheritance of ALD. Clearly label where your pedigree shows evidence of X-linked recessive or autosomal recessive inheritance.

2. Identify the genotypes for individuals II-4, II-5, III-11, III-12, IV-6, IV-7, IV-8, and IV-9 in one of the lines of inheritance on the pedigree. (Provide a key for the allele symbols you use.) Construct a Punnett square to predict the probability of individuals III-11 and III-12’s next child being a male with CH. Explain why more females than males inherit CH in generation III.

Use the following information to answer the next three questions.

Deaf-mutism is an autosomal recessive trait that is caused by two genes. Individuals who are homoxygous recessive for either gene will have deaf-mutism. The two genes are designated as D and E in the diagram below.

- from Huskey, 1998

3. A possible genotype of individual IV-3 is
   
   

   1. ddEE

   2. ddEe

   3. DDee

   4. DdEe

4. Individuals III-1 and III-2 are expecting their seventh child. What is the probability of this child having deaf-mutism?
   
   

   1. 0.00

   2. 0.25

   3. 0.50

   4. 0.75

Numerical Response

5. What is the probability of a couple that are heterozygous for both genes having a child with deaf-mutism?

Reflect on the Big Picture

By building a pedigree of a real family, you have put into practice your knowledge of genetics. You can now visually display inheritance for other people to see and follow.

Lesson Summary

During this lesson you explored the following focusing question:

• What technologies exist to help us explain and predict the inheritance of traits in breeding programs or family histories?

Pedigrees and Punnett squares are two excellent technologies that help us visually represent inheritance. They can be used to predict the probabilities of future expressions of a trait, and can also help determine the mode of inheritance of that trait.

Module Summary and assessment

Until Gregor Mendel conducted careful breeding experiments with garden peas, the moving of traits from one generation to another was a mystery. Using Mendel’s basic principles, we can now create more effective breeding programs for agriculture, or give meaningful council to young couples about the chances of their baby having a unique disorder. Combining those principles with Morgan’s evidence that genes occur on chromosomes, we can create tests for the presence of genes, and even target specific genes for transfer to other organisms. With the conclusion of the human genome project, we now have a complete map of all human genes. As scientists work to discover how genes work together and how each gene is expressed, we will come closer to understanding our complete genetic make-up, enabling us to better predict the results of future generations, and even manipulating those results to meet our needs and/or desires.

Assessment

For this module you should have completed the following assignments as well as submitted tutorial summaries for each tutorial video.

Bio30 3.6.2 online assignment

Bio30 3.6.3 online assignment

Bio30 3.6.4 online assignment

Bio30 3.6.5 online assignment

Bio30 3.6.6 online assignment

Bio30 3.6.8 online assignment

Bio30 3.6.9 online assignment

At the end of the next module you will complete the unit quiz and exam.