4. A Drosophila melanogaster female with cinnabar eyes is crossed to a D. melano

Question

4.   A Drosophila melanogaster female with cinnabar eyes is crossed to a D. melanogaster male with brown eyes.The F1 are all red-eyed.
The F1 are allowed to cross with each other, and produce the following offspring.
57 red eyed
14 brown eyed
13 cinnabar eyed
6 white eyed

One of the white eyed females is cross with one of the male F1. The results are as follows
23 red eyes
27 brown eyes
25 cinnabar eyes
25 white eyes.
a)   What genetic interaction is happening here? How many loci, how many alleles, and how do they interact?
b)   Diagram both crosses and explain the results.

Explanation / Answer

a) It seems that cinnabar (C) and brown (B) are on an independent locus, if they express together it gives an intermediate or mixed color that is red. It suggests that there is an incomplete dominance between CC and BB. But there is a white eye progeny, it might be due to independent assortment of a third allele 'W' on another locus. If it is there in (WW or Ww) homozygous or heterozygous state that would produce white eyed progeny when bb and cc present. 3 loci and 6 alleles would be present independently.

As I mentioned earlier, if C and B interacts that produce red, if they don't interact they produce either cinnabar or brown in both homozygous and heterozygous states. If white in heterozygous states will allow to produce either cinnabar/ brown/ red, but it produces white in heterozygous and homozygous when the cinnabar and brown alleles at recessive state.

b. You draw yourself using above data.

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