Module 6 Mendelian Genetics

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.