Answer to Question #157880 in Genetics for Leanne Howse

Question

The fur colour of Labrador dogs is determined by three alleles: black (FB), chocolate (FC) and yellow (FY). If black is dominant to yellow, and chocolate is dominant to yellow, what will the puppy colours be is a heterozygous chocolate Labrador and a yellow Labrador are bred?

Heterozygous chocolate parent genotype:

Yellow lab parent genotype:

Offspring phenotypes and ratios:

Answer 1

Solution:

Labrador with chocolate fur is heterozygous, which means that it has two different allel genes: one of them is chocolate (FC). There is no information about whether black (FB) fur colour is dominant to chocolate (FC) so it`s impossible to predict the phenotype of heterozygous Labrador with FB and FC allel genes. But the task says that FC is dominant to FY (yellow fur colour). It means that Labrador with FC and FY allel genes would have a chocolate fur colour. So heterozygous chocolate parent genotype is FC FY.

FB and FC are dominant to FY. Yellow fur phenotype manifests only if dominant genes are absent, so yellow parent phenotype is FY FY.

P (parents):

FC FY x FY FY

F₁ (offspring):

25% FC FY - chocolate fur

25% FC FY - chocolate fur

25% FY FY - yellow fur

25% FY FY - yellow fur

After adding the same genotypes:

50% FC FY - chocolate fur

50% FY FY - yellow fur

Answer:

Heterozygous chocolate parent genotype: FC FY

Yellow parent genotype: FY FY

Offspring phenotypes and rations: 50% chocolate puppies and 50% yellow puppies.