Module 6

Module 6—Mendelian Genetics: The Transmission of Traits to the Next Generation

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 the language of genetics.

 

You have begun to develop your skills with Punnett squares. Reflect on their usefulness when you are asked to consider traits that are not as simple as contrasting traits, or when more than one trait is considered in the cross. Consider ways that you could adapt the Punnett square to new situations.

 

Self-Check

 

To ensure your understanding of this lesson, answer the following questions.

 

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).

SC 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

 

1	2	3	4
DNA sequence for coat colour	TT, Tt	T	Tobiano (white spotting pattern)
	tt	t	Not tobiano (no white spotting pattern)

SC 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.

 

SC 3. The probability of two carrier parents having a child with sickle cell anemia is

1. 25%
2. 50%
3. 75%
4. 100%

Use the following information to answer question TR 6.

 

Cystic fibrosis is the most common genetic disorder among Caucasians, affecting one in 2000 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.

 

SC 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

 

Try This

 

TR 10. One of the essential skills in genetics is learning to apply what you know to new situations. For excellent review material conduct an Internet search using the terms “biology + Arizona + edu + Mendelian genetics + problem sets + monohybrid cross.” Many of the sites available offer help or a tutorial with each question. Complete the questions that are useful to you at this point in your studies.

 

Reflect on the Big Picture

 

In the Big Picture for this module you were asked to observe the variations in your family. Some people in your family look alike and some do not. Some have inherited certain traits or genetic conditions, and some have not. You have come to understand that some of these characteristics result from the inheritance of simple dominant or recessive alleles for a trait.

 

A key part to understanding inheritance is being able to determine what traits were present in past generations and predict which are likely to present themselves again in future generations. By learning to use Punnett squares and test crosses, you can determine the alleles present in parents and their offspring. In Lesson 5, you will learn how to apply these skills to determine probabilities and outcomes. For example, you could counsel a young couple on the probability of having a child with cystic fibrosis if you knew their genotypes (cystic fibrosis is a single gene trait). In this lesson, you learned how to conduct tests on plants to see if a strain is true breeding or not, and thus, whether or not it is worth keeping. You will apply the skills of this lesson to developing pedigrees and understanding family histories later in this module.

 

Module 6: Lesson 2 Assignment

 

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

 

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