In Drosophila melanogaster, black body (b) is recessive to graybody (b+), purple eyes (pr) are recessive to red eyes (pr+), andvestigial wings (vg) are recessive to normal wings (vg+). Thesethree genes are linked with pr located between b and vg at agenetic distance of 6 cM from b and 13 cM from vg. Previousexperiments have shown that the interference associated with thesethree genes is 0.5. A fly with a black body, purple eyes andvestigial wings is crossed with a fly with a gray body, red eyesand normal wings. All of their F1 progeny is wild-type. The F1females are mated with male flies that have black bodies, purpleeyes and vestigial wings. Ten thousand progeny are produced fromthis testcross. How many of the testcross progeny are expected tohave purple eyes but be wild-type for body color and wing type?
A. 19.5 B. 39 C. 78 D. 280.5 E. 561
