5. In fruitflies, the wildtype brick red eyes are due to the accumulation of two

Question

5. In fruitflies, the wildtype brick red eyes are due to the accumulation of two pigments, the brown pigment ommochrome and the red pigment pteridine. The cinnabar locus on autosome 2 encodes an essential enzyme for the production of ommochrome. Mutations in the cinnabar locus are usually recessive and result in flies with bright red eyes. The white locus on the X chromosome encodes a membrane pump that concentrates ommochrome and pteridine in the eyes. Mutations at the white locus are recessive and result in white eyed flies A dihybrid cross was conducted by mating true breeding cinnabar eyed males with a true breeding white eyed females. In the F1 generation, the females F1 were wildtype and the males were white eyed. What percentage (or fraction) of the male F2 flies would be wildtype? ($18 Exam)

Explanation / Answer

Let us consider a type CC for wild character WW for normal given condition(brick red) whereas cc stands for mutated recessive conditions (bright eye) while mutation in a white locus is represented by WW which gives a white eye. Initially by a cross between true breeding wild type male (CCWW) and true breeding white eyed female(ccww) gives wild type F1 offspring (CcWw). When this is crossed with white eyed male (ccww) gives 25% of wild type males. This can be verified by punnet square dihybrid crossby taking the above mentioned characters.

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