One of the genes controlling coat colour in cats is located on the X chromosome. The Xy allele of this gene produces yellow/orange coat colour and the Xb allele produces black coat colour. Heterozygous females have black and orange patches and are called tortoiseshell or calico. A litter of kittens consists of two calico females, and three yellow females. There is only one possible combination of parental phenotypes that would give rise to such a litter.

Question

anonymous · Answer

a. Using a punnett square, determine the phenotypes and genotypes of the parents. 
b. How would it be possible to have a male calico cat? Include the genotype in your answer. 

Someone, help? I'm so confused with this problem..

blues · Answer

The first thing to do is to list the genotypes associated with each phenotype.

1. A yellow female has two yellow alleles.
2. A black female has two black alleles
3. A calico female has one yellow allele and one black allele.

We don't need to bother with male cats, because we're told in the problem that all the offspring are females.

blues · Answer

The next thing to do is interpret what it means for the coat color allele to be on the X chromosome. The female kittens have two X chromosomes, one inherited from Dad and the other inherited from Mom. Moreover, we know that Dad has only one X chromosome to pass onto the daughter kittens whereas Mom has two.

That means that the Punnet Square we draw for the problem looks like this:

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