Coat color in mice is determined by two independently assort

Coat color in mice is determined by two independently assorting but interacting gene loci. The dominant gene (B) at one locus allows a colorless precursor to form black pigment while its allele b inhibits pigment formation and gives the albino phenotype when homozygous. The other locus, A allows pigment to be deposited in the wild or agouti pattern. In the absence of A (i.e., when aa is the genotype) only the blade pigment pattern occur in the fur. From the information given, draw the developmental (biochemical) pathway that leads to the wild or agouti coat pattern. Assume a series of crosses are made between two mice that are heterozygous at both gene loci. What phenotypes would be expected and in what numbers if 160 progeny were produced?

Solution

Answer:

A).

A_B_ = Agouti

A_bb or aabb=Albino

aaB_ = Black

B).

AaBb (agouti)     X AaBb (agouti)    

AB

Ab

aB

ab

AB

AABB, agouti

AABb, agouti

AaBB, agouti

AaBb, agouti

Ab

AABb, agouti

AAbb, albino

AaBb, agouti

Aabb, albino

aB

AaBB, agouti

AaBb, agouti

aaBB, black

aaBb, black

ab

AaBb, agouti

Aabb, albino

aaBb, black

aabb, albino

Agouti : black : albino = 9 : 3 : 4

Out of 160 progeny, 90 (agouti), 30 (black) & 40 (albino)

	AB	Ab	aB	ab
AB	AABB, agouti	AABb, agouti	AaBB, agouti	AaBb, agouti
Ab	AABb, agouti	AAbb, albino	AaBb, agouti	Aabb, albino
aB	AaBB, agouti	AaBb, agouti	aaBB, black	aaBb, black
ab	AaBb, agouti	Aabb, albino	aaBb, black	aabb, albino