Module 6

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

Reflect and Connect

 

Polygenic and epistatic traits help you understand the variation that can exist in individuals. The wide range of eye colour, hair colour, and skin colour in humans can be explained as polygenic traits.

 

When a walnut chicken was crossed with another walnut chicken, all four of the possible phenotypes for the comb found in chickens were produced. From your work with Mendelian genetics, you realize that these results would not be possible with any amount of alleles if this trait were controlled by a single gene. This type of inheritance is only possible if more than one gene is acting to affect the same trait. This is termed a polygenic trait.

 

The coat colour in many animals is explained through epistatic genes. If you have a cat, you may now be able to understand the variation that can occur in the phenotypes of a new litter of kittens.

 

Add any new terms to your flash cards. Review all the flash cards you have created to date and test yourself to ensure that you are mastering the concepts and vocabulary.

 

Before you begin the lesson assignment, to consolidate the concepts that you have learned about the principles of inheritance of traits and the tools used to study these principles, you might choose to do a selection of questions from pages 598, 606, and 609. Consult with your teacher as to which questions would best suit your review. You teacher will provide feedback to your responses.

 

OR

 

Apply your understanding of this lesson by completing the following Self-Check questions.

 

Self-Check

 

 

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.

 

SC 3. 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

SC 4. 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

 

SC 5. The genotypes of the parents of these F1 offspring could be

1. BBDD bbdd
2. BbDD bbdd
3. Bbdd bbDD
4. bbDD BBdd

SC 6. 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

Numerical Response

 

Use the following information to answer SC 7.

 

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

 

SC 7. 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).

 

 

 

Module 6: Lesson 8 Assignment

 

In this assignment you will work with the breeding of corn. You will be trying to produce taller corn plants, which are an important food and fuel crop.

 

Retrieve your copy of the 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.

 

Reflect on the Big Picture

 

In the Big Picture you wondered about all the variation in your family. Many of their characteristics, including skin colour, have a continuous phenotype. There can even be individuals with characteristics that don’t seem to be in any other family members. These characteristics are probably the result of polygenetic inheritance.

 

Polygenic inheritance is another example of an inheritance pattern that leads to a wide phenotypic variety in offspring. From your study of polygenic traits in this lesson, you should be able to understand how the expression of genes for traits such as human hair colour and eye colour can be influenced by many genes.

 

Going Beyond

 

Completing this question will build on your understanding on gene interaction.

 

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 a father with neither vitiligo nor albinism. 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

Module 6: Lesson 8 Assignment

 

Submit your completed Module 6: Lesson 8 Assignment to your teacher for assessment.

Biology 30 Learn EveryWare © 2009 Alberta Education