Question

Uption 4. The inheritance of hair and eye color is very complicated. Scientists have found approximately 10-20 genes responsible for determining hair and eye color in humans (sheesh - I thought a dihybrid cross with 2 genes was bad...). Although many genes are involved in producing these phenotypes, it does seem that just a few genes play a major role in determining the color of our hair and eyes. The following is a simplified, but still somewhat realistic view of how hair and eye color are inherited. Gene H (polygenic inheritance): A gene involved in determining hair color is located on chromosome 15. The more dominant alleles present for this gene, the darker the hair color. Individuals with the HH genotype have dark brown hair; individuals that are heterozygous have light brown hair, and individuals with the hh genotype have blond hair. Gene E (incomplete dominance): A gene involved in determining eye color is also located on chromosome 15. However, it is far from the hair color gene, so you can assume crossing over occurs often which functionally makes the genes for hair and eye color unlinked. Eye color is similar to genes that show incomplete dominance, where EE individuals have brown eyes, heterozygotes have green or hazel eyes, and individuals with the ee genotype have blue eyes. Gene A (epistasis): A third gene controls the expression of hair and eye color. It is located on chromosome 11, and codes for the production of the enzyme tyrosinase, which is responsible for creating melanin, or the protein that gives the color to your hair and eyes given whatever your genes code for. If at least one dominant allele "A" is present, then the individual will express the colors that code with their specific genotype for hair and eye color. However, if a person has the "aa" genotype, then they are considered an albino, and will have blond hair and blue eyes, no matter what sort of genotype they have for the H or E gene. For example, an individual with the AAHhEe will have light brown hair and green or hazel eyes. Question: Let's say a man that is heterozygous at all 3 gene loci mated with a female that had blond hair and blue eyes. However, based on the pedigree of her family we know that the female had to have been heterozygous for the Hand E genes. What is the chance this couple will produce a child with brown hair and blue eyes? Show your work (2 pts).

Answer 1

4) According to the question, genotype of man is AaHhEe (As he is heterozygous for all 3 gene loci). Now, as female must be heterozygous for H & E loci & also, she had blond hair (Phenotype of hh) & blue eyes (Phenotype of ee), she must be 'aa' for A locus. Thus, genotype of female will be aaHhEe.

Cross $\rightarrow$ AaHhEe x aaHhEe

Gametes $\rightarrow$ AHE, AHe, AhE, Ahe, aHE, aHe, ahE & ahe (From AaHhEe); aHE, aHe, ahE & ahe (From aaHhEe)

The cross between them is shown in below Punnett square.

Gametes	aHE	aHe	ahE	ahe
AHE	AaHHEE	AaHHEe	AaHhEE	AaHhEe
AHe	AaHHEe	AaHHee (Dark brown hair, blue eye)	AaHhEe	AaHhee (Light brown hair, blue eye)
AhE	AaHhEE	AaHhEe	AahhEE	AahhEe
Ahe	AaHhEe	AaHhee (Light brown hair, blue eye)	AahhEe	Aahhee
aHE
aHe
ahE
ahe

As cross between last four gametes of first column (Shown by red color) will produce all 'aa' genotype & hence will be albino, they are ignored for brown hair & blue eye calculation. From the above Punnett square, we find that probability of a child with brown hair & blue eyes will be 3/32.