In a Lab Strain of Drosophila,cinnabar (Cn)and Brown (Bw)are Recessive $$\begin{array} { l l l } + & + & 25,200 \\\text { cn } & b w & 21,009 \\\text { cn } & + & 11 \\+ & b w & 36\end{array}$$

Essay

In a lab strain of Drosophila,cinnabar (cn)and brown (bw)are recessive eye color mutations known to be 41 map units apart on chromosome 2.When similar mutant alleles were induced in a strain from nature,the same linkage of cn and bw was observed.However,when a wild-type strain from nature was crossed with a cn bw/cn bw lab strain to create the genotype + +/cn bw,and females of this type were testcrossed to cn bw/cn bw males from the lab strain,the following phenotypic proportions were obtained in the progeny:
$$\begin{array} { l l l } + & + & 25,200 \\\text { cn } & b w & 21,009 \\\text { cn } & + & 11 \\+ & b w & 36\end{array}$$
a)What is unexpected about these results?
b)What is the most likely explanation? (Summarize your model with a chromosome diagram with labelled genes.)
c)On your diagram show the precise origin of the cn + and the + bw classes.