Labrador retriever dogs have two genes that affect coat color. One gene, the B l

Question

Labrador retriever dogs have two genes that affect coat color. One gene, the B locus, codes for the intensity
of eumelanin production in the dog’s coat. It has two alleles that produce either a black pigment (B) or a
brown pigment (b). Another gene, the E gene, is epistatic to the B gene. The dominant E allele causes
eumelanin to be deposited along the length of the dog’s hair shafts. The recessive e allele blocks the
deposition of eumelanin in the hair, so only the yellow producing phaeomelanin pigment is deposited,
resulting in yellow dogs. If you cross parents with the following genotypes, Bbee x bbEe, what phenotypic
ratio do you expect in their offspring?

Explanation / Answer

Ans. The three recognized colour of Labrador retrievers is because of the difference in two genetic loci that affects the pigment expression. The first gene locus affects the colour of the dark pigment eumelanin and it is B locus. A second gene locus affects the expression of eumelanin pigment and it is E locus.

So, the three recognised colour of Labrador are:

1. Black-B/_:E/_

2. Brown - b/b:E/_

3. Yellow-__:e/e

So, the cross between

Bbee X bbEe

Gametes Be be X be bE

F1 progeny will be BbEe, bbEe, Bbee, bbee

BbEe- black phenotype

bbEe-brown phenotype

Bbee- yellow phenotype

bbee- yellow phenotype

Ratio will be :

For black phenotype =1/4

For brown phenotype =1/4

For yellow phenotype =2/4=1/2

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