Question

A special kind of dog usually has white fur. A specialty dog breeder notices two dogs of this breed with unusual colors. There is a blue dog with the genotype aaBB and an orange dog with genotype AAbb. The blue dog and orange dog are mated and their offspring have white coats.

Uppercase letters indicate dominant functional alleles while lowercase letters indicate recessive loss of function alleles.

The F1 white progeny are mated to each other to collect 160 dogs. Out of these, 90 have white coats, 40 have orange coats and 30 have blue coats.

Assuming that A and B segregate independently, which pathway(s) are consistent with the observation made in F2?

1. Blue -A-> Orange -B-> White

2. White -A(-)-> Blue -B(-)->Orange

3. Orange -E-> White -D(-)-> Blue

4. Both 1 and 3

5. Both 2 and 3

Answer 1

The phenotypic ratio is 90 : 30 : 40 = 9 : 3 : 4.

90 = white = A_B_

30 = blue = A_bb

40 = orange = aaB_, aabb

Epistasis is a non allelic interaction between alleles present at two different gene locus. Alleles present at one gene locus mask the effect of alleles present at other genes locus. The former are called epistatic and the latter are hypostatic.

Option 5 is right.

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