Part Genetics of Eye Color Their curiosity further piqued, Alexia and Evan conta

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Part Genetics of Eye Color Their curiosity further piqued, Alexia and Evan contacted Dr. Rick Sturm at the University of Queensland, a leading expert on eye color. It used to be thought that eye colour was what we call a simple Mendelian recessive trait-in other words, brown eye colour was dominant over blue, so a person brown eyes, and only two blues with no brown could produce blue eyes. But the model of eye colour inheritance using a single gene is insufficient to explain the range of eye colours that appear in humans. We believe instead that there are two major genes one modify this trait. The mechanism that determines whether an eye is brown or blue is like switching on a light, whereas an eye becoming green or hazel is more like Dr. Sturm (Sturm, quoted from: "Eyes Have i on Multiple Gene Question," nd). with two brown versions of the gene or a brown and a blue would have that controls for brown or blue, and one that controls for green or hazel -and others that unscrewing the light bulb and putting in a different one," said somcone To answer Alexia and Evan's question, he added: "So contrary to what used to be thought, it is possible for two blue-eyed parents to have a brown-eyed child, although this is not common.(Sturm, quoted from "Eyes Have it on Multiple Gene Question, n.d.). Hearing these words, Evan sighed in relief. Even though he trusted his wife, it was reassuring to hear one of the world's leading experts on the matter say that Ryan could be their son Dr. Sturm went on to explain that, contrary to what is taught in high school genetics classes, there are many genes involved in the determination of eye color. Two of them are most important in determining eye color The first gene, called OCA2 (or bry2 or EYC13), is on chromosome 15.Although the exact function of the OCA2 protein in the cell is not known, it seems to be involved in the production of melanin COCA2", z009). OCA2 exists in two allelic forms: brown or blue. The brown (B) allele stimulates the production of high levels of melanin. The blue allele (b) does not produce the OCA2 protein, leading to the loss of melanin production. The brown allele is dominant over the blue allele. The mutation that produces the blue allele is a single point mutation (from T to C) in the intron of a gene upstream from OCA2 called HERC2 (Eiberg et al.. 20o8; Strum et al., 2008). This point mutation occurs in a regulatory element for OCA2. The mutation prevents the binding of a helicase, which makes the DNA accessible to transcription factors for OCA2 transcription. The second gene, called ggy, is on chromosome 19 and comes in two forms: blue or green. Green (G) codes for a protein that results in the production of some melanin, and is dominant over blue (g), which codes for a protein that results in no production of the pigment. In effect, there is a hierarchy: the OCA2 gene is epistatic to the ggy gene (in other words, the product of the OCA2 gene masks the product of the ggy gene). If one allele at the OCA2 gene site encodes the brown eye trait, the alleles at the gey sites are irrelevant and the eyes are brown. However, if the alleles at the OCA2 site are bb, then the combination of alleles at the ggy site determines whether the eyes are blue or green (Starr, zo05) Questions 13. Which of the two genes is likely to have been the one referred to in high school genetics problems of eye color 14. Determine all the possible genotypes (at the OCA2 and ggy loci) for Alexia and Evan ts. Are the OCA2 and goy genes genetical 16. Make a Punnett square showing the genotypes of all possible children produced by this couple (show the OCA2 ly linked? Why or why not and gy gene loci in your Punnett Square). Determine the eye color of all possible children. 17 Can the OCA2 and gy genes explain why Ryan has brown eyes?

Explanation / Answer

Ans-13- the two genes that were studies in high school genetGen were brown and blue produced by OCA2.

Ans-14- the possible genotype will be Bb or bb from OCA2. One of them might have Bb and other will have bb. The allels from gry gene will be gb.

Ans-14 the recombination frequency of these genes are very low so they are not genetically linked to one another.

Ans-15 punnet square

Bg= brown

Bb= brown

gb= green

bb= blue

Ans-17 yes it can only be explained by these genes.as these are responsible for the eye colour production.

g b B Bg Bb b gb bb

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