Question

Multiple Choice: Two purebred lines are crossed, then the offspring are crossed to produce an F2. The phenotypic ratios of the F2 are 15:1. What are possible explanations for this finding?

a.) 2 loci epistasis

b.) small number of offspring and a statistically unlikely outcome

c.) all of the above

Answer 1

Answer:

2 loci epistasis

Explanation:

When a dominant allele at either of two loci can mask the expression of recessive alleles at the two loci, it is known as duplicate dominant epistasis. This is also called duplicate gene action. A good example of duplicate dominant epistasis is awn character in rice. Development of awn in rice is controlled by two dominant duplicate genes (A and B).

Phenotype 1 = A_B_ or A_bb or aaB_

Phenotype 2 = aabb

AABB x aabb ---Parents

AaBb--------------F1

AaBb x AaBb ---F1 selfcross

	AB	Ab	aB	ab
AB	AABB (phenotype 1)	AABb (phenotype 1)	AaBB (phenotype 1)	AaBb (phenotype 1)
Ab	AABb (phenotype 1)	AAbb (phenotype 1)	AaBb (phenotype 1)	Aabb (phenotype 1)
aB	AaBB (phenotype 1)	AaBb (phenotype 1)	aaBB (phenotype 1)	aaBb (phenotype 1)
ab	AaBb (phenotype 1)	Aabb (phenotype 1)	aaBb (phenotype 1)	aabb (phenotype 2)

Phenotype 1 = 15/16

Phenotype 2 = 1/16