Final answer:
The 9:7 phenotype ratio obtained in the F2 generation instead of the expected 9:3:3:1 ratio is due to complementary genes that interact with each other. The interaction between these genes modifies the expected phenotypic ratios.
Step-by-step explanation:
The 9:7 phenotype ratio obtained in the F2 generation instead of the expected 9:3:3:1 ratio is due to genes that interact with each other and do not follow the typical dominant and recessive pattern. These genes are called complementary genes.
In a dihybrid cross, the 9:3:3:1 ratio is observed when two independent genes segregate into gametes. However, when complementary genes are involved, the 9:7 ratio is observed because the interaction between these genes modifies the expected phenotypic ratios.
For example, if we consider the interaction between two complementary genes A and B, the ratios for the different phenotypes in the F2 generation would be:
- 9: round, yellow (A_B_)
- 3: round, green (A_bb)
- 3: wrinkled, yellow (aaB_)
- 1: wrinkled, green (aabb)