In some plants a red pigment is synthesized from a colorless precursor by a sing
ID: 193694 • Letter: I
Question
In some plants a red pigment is synthesized from a colorless precursor by a single enzyme coded for by gene A. The red pigment can be changed into a purple pigment by another enzyme coded for by gene B. A cross between pure-breeding purple plants and white plants with the resulting F2:
94 purple
31 red
43 white
A. Give a concise genetic hypothesis for inheritance of flower color from these results (include number of genes, number of alleles, and the relations between genes and alleles).
B. Using symbols A and B to correspond to genes A and B as described above symbolize the genotypes and their ratios for each F2 phenotypic class.
C. If the F1 is used in a testcross, what phenotypic ratio would you expect in the progeny?
Explanation / Answer
Answer:
The inheritance pattern is described about the recessive epistasis.
A).
Gene A consists of two alleles A(dominant) & a (recessive)
Gene B consists of two alleles B(dominant) & b (recessive)
When recessive alleles at one locus mask the expression of both (dominant and recessive) alleles at another locus, it is known as recessive epistasis.
A_B_ = Purple
A_bb or aabb = White
aaB_ = Red
B).
Purple (AABB) x White (aabb)
AaBb (purple) ---F1
F1 x F1
AB
Ab
aB
ab
AB
AABB (purple)
AABb(purple)
AaBB(purple)
AaBb(purple)
Ab
AABb(purple)
AAbb (white)
AaBb(purple)
Aabb (white)
aB
AaBB(purple)
AaBb(purple)
aaBB (red)
aaBb (red)
ab
AaBb(purple)
Aabb (white)
aaBb (red)
aabb (white)
Purple : Red : White = 9 : 3 : 4
C).
AaBb (F1) x aabb—Test cross
ab
AB
AaBb (purple)
Ab
Aabb (white)
aB
aaBb(red)
ab
aabb(white)
Purple : Red : White = 1 : 1 : 2
AB
Ab
aB
ab
AB
AABB (purple)
AABb(purple)
AaBB(purple)
AaBb(purple)
Ab
AABb(purple)
AAbb (white)
AaBb(purple)
Aabb (white)
aB
AaBB(purple)
AaBb(purple)
aaBB (red)
aaBb (red)
ab
AaBb(purple)
Aabb (white)
aaBb (red)
aabb (white)
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