In Labrador retriever dogs, coat color is determined by the interaction of two genes (pigment and deposition of pigment). This is called epistasis. Coat color can be black (B) or brown (b) and deposition of pigment into the hair shaft is deposited (E) or not deposited (e). If a retriever has the genotype where they have _ _ ee, then they will have a yellow coat regardless of what color they inherit (e.g., Bbee or bbee gives a Yellow lab).

1. Calculate the phenotypic ratios of a cross between a male and a female Labrador retrievers that are both heterozygous for coat color and heterozygous for deposition of pigment.

What is the genotype of both the male and female parents?

What are the possible gametes of both the male and female parents?

What is the phenotypic ratio of the offspring?

As both are heterozygous therefore Male genotype will be (BbEe) and the genotype of female will be (BbEe). While both will have the phenotype black.

Parent Genotype

Male X Female

BbEe X BbEe

Possible gametes from Parents

Male X Female

BbEe X BbEe

(BE) (Be) (bE) (be) X (BE) (Be) (bE) (be)

...

F1 generation will have following genetypic ratio

Black Labrador = 9 = B_E_

Brown Labrador = 3 = bbE_

Yellow Labrador = 3 = B_ee

Yellow Labrador = 1 = bbee

Furthermore, the phenotypic ration will be

Black Labrador = 9

Brown Labrador = 3

Yellow Labrador = 4