Q$3\mathrm{.}3$: $(16$ total points$)$ In Drosophila, the recessive mutant genes $\backslash ($ b $\backslash )($black body$),\backslash ($ r $\backslash )($rosy eye$)$ and ap $($apterous wing$)$ are linked on chromosome $2.$ A female fly known to be heterozygous for all three traits was mated with a male known to be homozygous recessive for all three traits. The offspring from this cross are shown below.

A$.$ Which gene is in the middle? $(3$ points$)$

B$.$ Write the genotype of the heterozygous female in this cross $($use linkage notation$).(3$ points$)$

C$.$ Write a genetic map of this region of chromosome $2$ showing distances in map units between these genes. $(5$ points$)$

D$.$ Calculate the interference of crossing$-$over in this cross. $(5$ points$)$