Dosage compensation in mammals typically involves the random inactivation of one of the two X chromosomes relatively early in development.Such X chromosome inactivation often leads to phenotypic mosaicism.Assume that black fur in cats is due to the X- linked recessive gene b,whereas its dominant allele B produces yellow fur. A Bb heterozygote is a mosaic called "tortoise shell" or "calico." A mating between a black male and a calico female occurred.Give the phenotypes of the offspring.

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Since the male parent is black, he must have the genotype bb. On the other hand, the female parent is calico which means she must be Bb. However, since X-chromosome inactivation is random, she could have either the B or b allele inactive in different cells of her body. This means some of her eggs will carry the B allele and some will carry the b allele. 
Therefore, the offspring will be a mixture of males and females with either Bb or bb genotypes. The Bb offspring will be calico females, while the bb offspring will be either black males or black females. The yellow fur phenotype is not possible in this scenario, so options A, B, and D can be eliminated. The only choice that includes black offspring is C.

Dosage Compensation in Mammals Typically Involves the Random Inactivation of One