Part I High School Blues Evan and Alexia had been happily m

Part I – High School Blues

Evan and Alexia had been happily married for seven years and had a delightful ve-year-old son named Ryan. One day, while going through his old high school biology textbook, Evan stumbled on some troubling information. In the section on the genetics of eye color, he read that two blue-eyed parents cannot produce a brown-eyed child. is was disturbing to him because both he and Alexia had blue eyes, but Ryan had brown eyes.

He and Alexia were very much in love and Evan didn’t believe his wife had been unfaithful. Puzzled, he questioned his wife, who con rmed she had been faithful to him. Evan had known Alexia long enough to recognize when she was lying and detected nothing but honesty in her response.

What is going on?

Questions

1.What protein does the “eye color gene” encode? Propose what the function of this protein might be, and how this protein might di er in people with brown and blue eyes.

2.Which is dominant and which is recessive: the blue eye allele or the brown eye allele?

3.If Evan has blue eyes, what genotype (which two alleles) is he likely to have?

4.If Alexia has blue eyes, what genotype (which two alleles) is she likely to have?

5.Draw a Punnett square showing the genotype of all the possible children this couple could have. Based solely on this information, what is the likelihood that Ryan is their child?

6.Assuming that Alexia has been unfaithful, what is (are) the possible genotype(s) of the man who is Ryan’s biological father?

7.Assuming that Alexia has been faithful, suggest as many hypotheses as you can to explain Ryan’s phenotype.

Solution

(1) There are two eye colour gene OCA2 and the other is gey.OCA2 is present on chromosome 15 and gey gene is present on chromosome 19.The exact function of OCA2 is not clearly known but it is believed to code for melanin.it exist in two allelic form ( B) stimulates the high level of melanin and (b) does not produce the melanin thus guving the blue colour to the eyes. gey gene is present on chromosome 19.It comes in two forms (G) green codes for the production of melanin and blue (g) that doesnt produce melanin.

(2) The brown eye allel (B) is dominant over blue eye (b) allel.The person with (BB) or (Bb) will possess brown eye and (bb) will possess blue colour eye.

(3) The genotype will be (bb) because blue eye colour is a recessive allel and it will only be expressed when it is in homozygous state.

(4)The genotype will be (bb) because the blue eye colour is a recessive allel and it will only be expressed when it is in homozygous state.

(5)

all children will be blue eye coloured because it is a recessive trait and parents can have blue colour eyes if the alles are in homozygous form.

(6) The possible genotypes could be (BB) OR (Bb).

(7) HYPOTHESIS 1: MUTATION: There might be mutation in eye colour gene in the egg or the sperm which might have passed to the child and resulted in brown colour eye.