Hair pigmentation in mammals follows the generic enzymatic pathway depicted belo
ID: 204113 • Letter: H
Question
Hair pigmentation in mammals follows the generic enzymatic pathway depicted below. Enzyme A synthesizes a black pigment from a precursor, and the contribution of enzyme B results in the final agouti pigment:
Precursor molecule (colorless) Black pigment Agouti pigment
Each enzyme is coded by a single allele with complete dominance. If a crossing design begins with true breeding parents for coat color with the genotypes AAbb and aaBB. What will be the expected F2 genotypic and phenotypic ratios of the eventual F2 progeny?
Explanation / Answer
Answer:
A_B_ = Agouti
A_bb = black
aaB_ or aabb (colorless)
AAbb (black) x aaBB (colorless)---Parents
Ab aB -----------------Gametes
AaBb (agouti)-----------F1
AaBb x AaBb -----Selfcross
AB
Ab
aB
ab
AB
AABB (agouti)
AABb (agouti)
AaBB (agouti)
AaBb (agouti)
Ab
AABb (agouti)
AAbb (black)
AaBb (agouti)
Aabb (black)
aB
AaBB (agouti)
AaBb (agouti)
aaBB (colorless)
aaBb (colorless)
ab
AaBb (agouti)
Aabb (black)
aaBb (colorless)
aabb (colorless)
Agouti = 9/16
Black = 3/16
Colorless = 4/16
AB
Ab
aB
ab
AB
AABB (agouti)
AABb (agouti)
AaBB (agouti)
AaBb (agouti)
Ab
AABb (agouti)
AAbb (black)
AaBb (agouti)
Aabb (black)
aB
AaBB (agouti)
AaBb (agouti)
aaBB (colorless)
aaBb (colorless)
ab
AaBb (agouti)
Aabb (black)
aaBb (colorless)
aabb (colorless)
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