Question

While exploring the Antarctic, you discover a species of small flowers that are yellow, purple, or white according to the following pathway with A and B Genes. A promotes the transition from purple to yellow and B inhibits the transition from yellow to white. You cross true breeding yellow flowers with true breeding purple flowers. All of the F1 offspring are yellow. You cross the F1 yellow flowers to each other and see the following offspring: 94 -yellow 41-purple 29-white What are the genotypes of the following plants? True breeding yellow parent: True breeding purple parent: Yellow F1s: White F2s: What kind of gene interaction do A and B have (additive, recessive epistatic, reciprocal recessive epistatic, dominant epistatic, or redundant)? Explain your answer.

Answer 1

A promotes the transition from purple to yellow and B inhibits the transition from yellow to white so yellow flowers have both A and B functional genes and these plants are true-breeding so the genotype of the yellow plant is AABB and the purple plant does not have A and B functional genes to convert purple pigment so the genotype of purple plant is aabb

AABB * aabb

AaBb ( F1 progeny)

genotype of F1 progeny is AaBb

AaBb * AaBb

	AB	Ab	aB	ab
AB	AABB (yellow)	AABb (yellow)	AaBB (yellow)	AaBb (yellow)
Ab	AABb (yellow)	AAbb (white)	AaBb (yellow)	Aabb (white)
aB	AaBB (yellow)	AaBb (yellow)	aaBB (purple)	aaBb (purple)
ab	AaBb (yellow)	Aabb (white)	aaBb (purple)	aabb (purple)

yellow F2s are AABB, AABb, AaBB,AaBb, and white F2s are AAbb, Aabb.

this is an example of dominant epistasis when the dominant allele B is present then it prevents the formation of white pigment so the phenotype depends on the B locus

and the ratio expected based on dominant epistasis is  yellow:purple:white= 9:4:3 and ratio observed is

yellow:purple:white: 94:42:29 this is almost equal to 9:4:3

so this is an example of dominant epistasis.