Question

Imagine the autosomal dominant CB allele produces black coat color in dogs, and the recessive Cw allele produces a white coat color. The CB allele is also recessive for lethality; pups with the CBCB genotype die well before birth, and their remains are resorbed by the mother’s uterus. Imagine you cross heterozygous black male dog with a heterozygous black female. What ratio of genotypes and phenotypes do you expect to see in the F1 offspring? If more than one genotype produces the same phenotype, list all the genotype/phenotype combinations separately.

Answer 1

the ratio of genotypes will be 2:1 (CBCw:CwCw) and the phenotype ratio will be 1:1 (black dog:white dog)

Step-by-step explanation:

If heterozygous black male dog is crossed with a heterozygous black female then:

P: CBCw x CBCw

F1: CBCB CBCw CBCw CwCw

Since CBCB genotype will die before birth, the ratio of genotypes will be 2:1 (CBCw:CwCw) and the phenotype ratio will be 1:1 (black dog:white dog).

CBCw genotype, which is heterozygous will produce black phenotype, since the allele CB is dominant over Cw allele.