Genetic explanation

F2 genotypes

AABB

AABb

AaBB

AaBb

AAbb

Aabb

aaBB

aaBb

aabb

Complete dominance lacking at either locus, no epistasis, phenotypic and genotypic ratios are equal

1

2

2

4

1

2

1

2

1

Complete dominance lacking in A, complete dominance in B, no epistasis

3

6

1

2

3

1

Complete dominance in A and B, no epistasis

9

3

3

1

Recessive epistasis, aa epistatic to B and b

9

3

4

Dominant epistasis, A epistatic to B and b

12

3

1

Dominant and recessive epistasis, A epistatic to B and b, bb epistatic A and a, A and bb produce identical phenotypes

13

3

Duplicate recessive epistasis, aa epistatic to Bb, bb epistatic to A and a

9

7

Duplicate dominant epistasis, A epistatic to B and b,  B eptistatic to A and a

15

1