Fruit Flies Normally Have Red Eyes -Which Strains' Mutations Represent a Complementation Group?
A)C, D, F

Fruit flies normally have red eyes.Seven different true-breeding strains of fly with white eyes have been identified (A-H) .In each strain, the white eye trait is due to an autosomal recessive allele.It is possible that all seven strains have mutations in the same gene.Alternatively, some or all of the strains may have mutations in different genes.To determine how many genes are involved in eye color in these flies, all possible pairwise crosses are performed.The offspring phenotypes resulting from each cross are observed.(+ = wild-type; ? = mutant)
$$\begin{array} { | c | c | c | c | c | c | c | c | c | } \hline & \mathrm { A } & \mathrm { B } & \mathrm { C } & \mathrm { D } & \mathrm { E } & \mathrm { F } & \mathrm { G } & \mathrm { H } \\\hline \mathrm { A } & - & - & + & + & - & + & + & - \\\hline \mathrm { B } & & - & + & + & - & + & + & - \\\hline \mathrm { C } & & & - & - & + & + & + & + \\\hline \mathrm { D } & & & & - & + & + & + & + \\\hline \mathrm { E } & & & & & - & + & + & - \\\hline \mathrm { F } & & & & & & - & - & + \\\hline \mathrm { G } & & & & & & & - & + \\\hline \mathrm { H } & & & & & & & & - \\\hline\end{array}$$
-Which strains' mutations represent a complementation group?

A) C, D, F
B) A, B
C) E
D) A, B, E, G, H