a+, b+, c+ and d+ are independently assorting Mendelian genes controlling the production of a black pigment. The alternate alleles that give abnormal functioning of these genes are a, b, c, and d. A black individual of genotype a+/a+ b+/b+ c+/c+ d+/d+ is crossed with a colorless individual of genotype a/a b/b c/c d/d to produce a black F1. F1 x F1 crosses are then done. Assume that a+, b+, c+ and d+ act in a pathway as follows: colorless –a+–> colorless –b+–> colorless –c+–> brown –d+–>black.
a. what proportion of the F2 generation will be colorless?
b. what proportion of the F2 generation will be black?
c. what proportion of the F2 generation will be brown?