Question

10) In Labrador retriever dogs three common coat colors are observed: black, chocolate, and gold. A cross between two black labs produces a ratio of 56 black: 19 brown: 25 gold. (2 pts) a. Based on the observed ratio among the progeny, which common type of epistasis is operating here? That is, which kind of modified dihybrid ratio most closely fits these data? b. List the genotypic classes among the offspring (F2) and give the corresponding phenotype of each (Hint: You only need to give the 3 found in the F2, not every single specific genotype).

Answer 1

Answer-

According to the given question-

Here we have a Labrador retriever, having coat color - Black, chocolate and gold. The yellow or gold color is due to the recessive epistatic gene which is responsible for masking the black color gene as well as chocolate color gene. The Blackcoat color (B) is dominant to chocolate coat color (b).

The coat color of Black - B_E_

The coat color of Chocolate - bb_E

The coat color of Gold - _ _ee

When we make a cross between two black color labs we get following offspring-

Black = 56

Brown = 19

Gold = 25

Total = 56 +19+25 = 100.

Cross between Black color labs i.e. between BbEe $\times$ BbEe.

	BE	Be	bE	be
BE	BBEE (Black coat color)	BBEe (Black coat color)	BbEE (Black coat color)	BbEe (Black coat color)
Be	BBEe (Black coat color)	BBee (Gold coat color)	BbEe (Black coat color)	Bbee (Gold coat color)
bE	BbEE (Blackcoat color)	BbEe (Blackcoat color)	bbEE (Chocolate coat color)	bbEe (Chocolate coat color)
be	BbEe (Blackcoat color)	Bbee (Gold coat color)	bbEe (Chocolate coat color)	bbee (Gold coat color)

Here we get 9: 3 : 4 Instead of a typical dihybrid cross of mendal of 9 : 3: 3: 1, with the phenotype of Blackcoat color: Chocolate coat color: gold coat color.