Assume that the length of a type of cucumber at maturity is controlled by three genes (a, b, and c), each of which has two alleles. the a, b, and c alleles each add 2 inches of cucumber growth, while the a, b, and c alleles add only 1 inch. a true-breeding 6-inch strain is bred to a true-breeding 12-inch strain. all the f1s produce 9-inch cucumbers. what sizes would you expect to see in the mature f2s?