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? (S18 Exam)

Explanation / Answer

ANSWER

as given in the above question that all the F1 progeny females are wild and males are white eyed indication criscross type inheritance due to x linked mutation

now by self crossing white eyed males with wild hetergygous femals of f1 , 50% of males will be white eyed because of hetergygous female , so half of population of F2 males will be white eyed

as we are awear about that heterygous femals contain two x chromosemes ,that will segregrate during egg formation. half among these eggs will have mutant x while other half will be normal. on the other hand males are white eyed in F1 and they only contain mutant X chromosome as given to them by their mother parent. on crossing F1 , the chriscross inheritance will become and all the males gets chromosomes from the hetergygous mother , from which half of males will be mutant white.

xy(normal) * xx (mutant)

F1 xY (mutant male) , Xx ( hetergygous normal female )

gametes x, Y and X, x

F2 .. as all males gets Xchromosome from mother

so

XY, xY will form males and 50% will be normal and 50% will be mutant

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