What additional evidence would help support the claim that these organisms share a common ancestor?

Homologous structures provide evidence for common ancestry, while analogous structures show that similar selective pressures can produce similar adaptations (beneficial features). Similarities and differences among biological molecules (e.g., in the DNA sequence of genes) can be used to determine species' relatedness.

A) two genes are involved with 12:3:1 epistasis, such that A_B_ and A_bb are black, aaB_ is brown, and aabb is green .

Explanation:

The F2 proportions approximate 12:3:1 ratios:

•239/320 ≅ 12/16

•61/320 ≅ 3/16

•20/320 = 1/16

These ratios are explained by dominant epistasis: if one gene has a dominant allele, then the expression of another gene will be masked, regardless of what alleles that second gene has.

The pure-breeding crosses were:

P  AABB x aabb

F1      AaBb

F1 x F1 crosses

AaBb x AaBb

F2 (from Punnett Square):

9 A_B_  black

3 A_bb  black

3 aaB_  brown

1 aabb  green

12/16 individuals of the F2 are black, 3/16 are brown and 1/16 is green