5. The black and yellow pigments in the coats of cats are controlled by a sex-li

Question

5. The black and yellow pigments in the coats of cats are controlled by a sex-linked pair of alleles. Females heterozygous for these alleles have areas of black and areas of yellow in their coats (tortoise shell or calico). A calico cat has a litter of eight kittens: 1 yellow male, 2 black males, 2 yellow females, and 3 calico females. Assuming there is a single father for the litter, what is his probable color? 5b. A yellow female cat has a litter of 4 kittens, 1 yellow and 3 calico. Assuming a single father for the litter, what is the probable sex of the yellow kitten?

Explanation / Answer

Ans 5:

(a) probable color of father is yellow.

Explanation:

Let the allele for black be Xb, and allele for yellow be Xw.

It is given that the female is Calico (XbXw) , but the litter comprises of two yellow females (XwXw). Since female parent can pass only one Xw allele, so in order for a female offspring to be XwXw, the other Xw must come from male parent. And, XwY male will be yellow. (If the male parent were black, then we would have observed only Calico or black female offspring.)

Ans (b)

Probable sex of yellow kitten = male .

Explanation:

Female parent is yellow , or XwXw.

Offspring includes 3 Calico (XbXw). Thus all Calico are females ( males cannot be heterozygous for X linked ). Hence, male parent must have been XbY.

Hence, in the offspring all males will be XwY (yellow) and all females will XwXb (Calico).

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