Dosage compensation leads to a variety of interesting coat color patterns in certain mammals. For instance, a female cat that is heterozygous for two coat color alleles, say black and orange, will usually have the "calico" or mosaic phenotype. Describe the chromosomal basis for the mosaicism (calico) in the female. Explain why chromosomally normal male cats do not show the mosaic phenotype, but XXY male cats can be "calico."

Explanation:

The genetic determination of coat colors in calico cats is linked to the X chromosome wherein calicos are nearly always female, with one coat color  allele linked to the maternal X chromosome and a second coat color allele linked to the paternal X chromosome.

Since, the females possess two X chromosomes (XX), they can be either homozygous for each coat colour or be heterozygote (calico). But in the males, since this trait is X- linked and males have just the one X chromosome (XY), they can only possess either of the coat colour and not be an heterozygote. But an XXY male cat can be a calico due to the presence of the two X chromosomes.

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