Question

#1. You have two pure-bred dog strains of Labrador retriever: Yellow (BBee) and Brown (bbEE). You friend wants to have a pure-bred puppy with black coat color. Let’s assume this set of coat color variations follows recessive epistasis with the allele ‘ee’ masking B or b.

A) provide breeding schemes
B) after breeding experiments, provide a scheme of identifying the pure-bred one with black

color. Also, what is the frequency of the pure-bred one among the black puppies.

#2. In the rat, the gene for the pigment (P) is dominant to no pigment (p). The gene for black

(B) is dominant to the gene for cream (b). If a pigment gene (P) is absent, genes B and b are inoperative or non-functional, resulting in albino phenotype.

A) What kind of inheritance patterns is this? Provide a brief explanation.
B) Provide the genotype and phenotype of the F1 of a cross between homozygous black rat

and an albino homozygous for cream.

C) If you self-cross the F1 describe above, what kinds of rat will you see in terms of genotype and phenotype?

Answer 1

A cross between Pure bred Yellow labrador (BBee) and Brown labrodor (bbEE) will result in mix Bred Black labrador (BbEe). This bred if back crossed with Pure bred Yellow labrador will result in pure bred Black Labrador with BBEe genotype with 25% frequency.

In order to identify pure bred Black labradors, lets try and understand the cross between mix bred black labrodor and pure bred yellow labrador:

Gamete genotype	BE	Be	bE	be
Be	BBEe	BBee	BbEe	Bbee
	Pure bred black	pure bred Yellow	mix bred black	mix bred yellow

When pure bred Yellow labrodors are crossed with pure bred black labradors, resulting progeny is of either black labradors or yellow labradors but not brown labradors.

Gamete genotype	BE	Be	bE	be
Be	BBEe	BBee	BbEe	Bbee
BE	BBEE	BBEe	BbEE	BbEe

Inhertance pattern among pigment genes is called epistasis. P is epistatic gene as functionality of B or b gene is dependent on P.

Genotypes:-

Homozygous black rat: PPBB

homozygous albino cream rat: ppbb

Resulting F1 progeny genotype: PpBb. phenotype- Black rat.

Self crossed PpBb will result in following genotypes:

Gamete genotype	PB	Pb	pB	pb
PB	PPBB	PPBb	PpBB	PpBb
Pb	PPBb	PPbb	PpBb	Ppbb
pB	PpBB	PpBb	ppBB	ppBb
pb	PpBb	Ppbb	ppBb	ppbb

Phenotype: Black, cream or albino skin rats