4Q What are the genotypes of the parents if two white flowered sweet pea plants produce only purple offspring in the F1 and which, if selfed, produce a purple to white ratio of 9:7?
1. AABB x aabb
2. AaBb x aabb
3. AAbb x aaBB
4. AABB x AABB
5. None of the above
CORRECT! The cross involves two interacting dominant genes in order to produce the purple color. If either parent, then, carried both an A and a B gene, it would have been purple. However, both parents were white and produced purple only in the F1. Hence the F1 would have to be exclusively heterozygous with each dominant coming in from a different parent.