The gene for body color and wing shape reside on the same chromosome in fruit flies. After crossing female flies having gray bodies and normal wings with male flies having black bodies and vestigial wings, Morgan observed that some of the F1 flies had nonparental phenotypes (gray bodies with vestigial wings, or black bodies with normal wings). What accounts for this?

a. The alleles underwent independent assortment during meiosis.

b. Some flies with those phenotypes accidentally contaminated the cross.

c. The alleles for wing shape and body color recombined by crossing over.

d. A certain percentage of the F1 generation was affected by genetic mutations.