Question

The following alleles of an autosomal locus affecting coat color are listed in descending order of dominance:

C (black) > ck(sepia) > cd(cream) > ca(albino)

A cross between a black male and a sepia female produced litters having 14 black, 8 sepia, and 6 albino progeny. What are the exact genotypes of the parents with regard to this locus? Please show steps in figuring out this problem.

a. Cca male X ckca female

b. Cck male X ckca female

c. CC male X ckck female

d. Ccd male X ckcd female

Answer 1

Here the male is having a black coat colour indicating that it has atleast one C allele. The female has sepia coat colour which indicates that they have no C allele and they have atleast one ck allele. Their offsprings shows 6 albino progeny, which indicates that these progeny received one ca allele from father and one ca allele from mother. Hence the exact genotype of the father becomes Cca and that of the mother becomes ckca.

The cross between them shows the following

Male/Female gametes	ck	ca
C	Cck (Black)	Cca(Black)
ca	ckca(Sepia)	caca(Albino)

The phenotypic ratio of Black:Sepia:Albino is 2:1:1, and here the offspring ratio becomes 14:8:6 which is similar to the expected ratio.

Hence the correct option is A