In rabbits, an allelic series helps to determine coat color C (black), cch (gray

Question

In rabbits, an allelic series helps to determine coat color C (black), cch (gray), ch (beige) and c (white). The dominance hierarchy is C>cch>ch>c. (C is dominant over all other alleles, cch is dominant over ch and c, and ch is dominant over c). The rabbits with the following phenotypes were crossed to produce the progeny shown. Give the genotypes of the parents and offspring for each cross: Parental Phenotypes Phenotypic ratios of offspring black x white 1/2 black, 1/2 white beige x white 1/2 beige, 1/2 white black x white 1/2black, 1/2 gray black x beige 1/2 black, 1/4 beige, 1/4white black x black 3/4black, 2/4 white

Explanation / Answer

For a both must be homozygous for their respective alleles so genotype is CC and cc b. Same as a both homozygous chch and cc c. The white parent must be cc because you cannot be white without the genotype cc. The black parent must therefor have one black allele and one gray allele so Cch and cc. d. The black parent must have a white allele because you need two white alleles to have white. The other allele for the black parent is black. The beige parent must have a beige allele and a white allele, the white allele gives rise to the 1/4 white and the beige gives rise to 1/4 beige. So Cch and chc. e. Both are heterozygote. So Cc and Cc.

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