Question

There is a sex-linked gene in controlling a cat's coat colour. Xy allele produces yellow/orange & Xb produces black coat colour. Heterozygous females have both black & orange patches and are called "calico". There is only 1 possible combination of parental phenotypes to give such a litter. Determine the phenotypes and genotypes of the parents.

Answer 1

Is there any more information? You have told us what phenotypes are associated with what genotypes, but you haven't told us how many offspring of each sex and coat color there are in the problem.

Answer 2

The offsprings are 2 calico females and 3 yellow females. Sorry!

Answer 3

OK.

So you know that all the female kittens have two X chromosomes, one from each parent. The yellow kittens have yellow alleles on both X chromosomes; the calico kittens have a black allele on one X and a yellow allele on the other X. That is just interpreting the info given in the problem.

Now worry about how they came to get those different chromosomes.

You know that the one they got from their Dad is the only X chromosome he has. Because some of the kittens are all yellow (two yellow alleles), you know that the X Dad gave them has a yellow allele on it. Therefore, Dad has one X chromsome with a yellow allele on it and a Y chromosome (because he is male) and he has a yellow coat.

The yellow kittens also got a yellow allele on the X they got from Mom, so you know she has at least one yellow allele.

The calico kittens must have got, in addition to the yellow alleled X froM Dad, a black alleled X which must have come from the mother cat. So Mom is heterozygous (one yellow allele and one black allele on each X chromosome) and is herself a calico cat.

Clear?

Answer 4

Oh my god. This all makes so much sense now. Thank you!