Kernel color in wheat is determined by two genes, with two alleles of each (A 1 , A 2 , B 1 , B 2
). Each 1 allele contributes an equal dose of color and each 2 allele contributes no color. The greater the number of 1 alleles, the deeper the color. If double heterozygotes (A 1 A 2 B 1 B 2
) are selfed, what proportion of the progeny will have exactly two doses of color (two 1 alleles)?