Question

Laborador retrievers come in 3 colors-black, brown or golden. Gene B determines what color of pigment is produced, with black being dominant over brown. Gene C determines pigment deposition, with the prescense of the dominant allele resulting in pigment deposition and homozygous recessive resulting in a golden appearance (no deposition).

a) which gene is epistatic to which?

b) If a Bbcc individual is crossed with a bbCc, what proportion of the progeny will be black, brown of golden?

c) you cross a brown dog with a golden dog and get all black puppies (assume that this isn't a coincidence and that you can ONLY get black puppies from this mating). What are the possible genotypes of the parents? you must show your work for credit.

Answer 1

1)Gene B produces two types of pigments black and brown independent of Gene C. However if Gene C is present in dominant form the pigment produced by gene B is deposited but if Gene C is in homozygous recessive form then pigment produced by Gene B is not deposited even if it produces some pigment leading to golden colour of the coat. Therefore Gene C in recessive form is masking the effect of gene B and is epistatic to gene B.

2) Bbcc x bbCc

Gametes of Bbcc : Bc , bc

Gametes of bbCc : bC, bc

	Bc	bc
bC	BbCc (black)	bbCc ( brown)
bc	Bbcc ( golden)	bbcc ( golden)

Phenotypic ratio - 1 black : 2 golden : 1 brown

3) If all puppies are black their genotype must be B_C_ . Underscore represent any recessive or dominant allele.

The possible genotype of puppies are : BBCC , BbCc, BBCc, BbCC

BBCC genotype puppies can be produced if both the parents are BBCC

BbCc genotype puppies can be produced one parent is BBCC and other is bbcc

BBCc genotype puppies can be produced if one parent is BBCC and other is BBcc

BbCC genotype puppies can be produced if one parent is BBCC and other is bbCC