Question

2. In Labrador dogs, there are 2 loci that determine coat color. The first locus, B is dominant to b. At least one B allele will produce black coat color, while the bb genotype produces a chocolate coat color. This first locus also determines nose color in Labradors: B_ black noses, and bb brown noses. The second locus has a genotype, ee, that is epistatic in nature. Any Labrador with an ee genotype will be yellow. A genotype containing at least one E allele will not affect coat color in Labradors.

You own a male, black Labrador that has been mated to three females producing the following progeny:

Litter Female color Pups

1 Black 10 all black pups

2 Brown 10 all black pups

3 Yellow (brown nose) 5 black pups, & 5 yellow pups with black noses

a) What is the sire’s genotype?

b) What is the probable genotype for the brown female (the mother of litter 2)?

c) What phenotypic ratio is expected if a black male and a yellow female from litter 3 were to be mated? (show work)

Answer 1

black labrador mated to three females, progenies from the third female includes yellow pups with black noses the black male parent is heterozygous at the E locus, otherwise, it cannot have progenies with ee genotype and progenies from female 1 and 2 are all black, and with the third female there are black pups and yellow pups with black nose, so the black parent has to homozygous at the B locus so that all progenies will have B allele.

a) genotype of the black male is BBEe.

b) brown female, has all black pups so her genotype is bbEE.

BBEe * bbEE

	BE	Be
bE	BbEE (black)	BbEe ( Black)

c) black male * yellow female from litter 3

the yellow pups from the litter 3 has a black nose, this shows the presence of B allele and their yellow mother has a brown nose so they are heterozygous at the B locus, their genotype is Bbee, the black pups have both B and E allele so their genotype is BbEe

BbEe * Bbee

	BE	Be	bE	be
Be	BBEe (black)	BBee (yellow)	BbEe (black)	Bbee (yellow)
be	BbEe (black)	Bbee(yellow)	bbEe (brown)	bbee(yellow)

the phenotypic ratio is

black: yellow:brown=3:4:1