Suppose you don't know how many loci underlie the purple-white color variation. You repeat the cross just described (pure Psà red F1sà F2s). In 1000 progeny you raise, none are purple or white. What does this tell you about the number of loci?
1) It tells you nothing
2) It's probably 3 or less –since (1/4)3 = 1/64
3) It's probably more than 4 –since (1/4)4 = 1/256
4) Its probably more than 6–since (1/4)6 = 1/4096