The Notch mutation is a deletion on the X chromosome of Drosophila melanogaster.

Question

The Notch mutation is a deletion on the X chromosome of Drosophila melanogaster. Female flies heterozygous for Notch have an indentation on the margins of their wings; Notch is lethal in the homozygous and hemizygous conditions. The Notch deletion covers the region of the X chromosome that contains the locus for white eyes, an X-linked recessive trait. Give the phenotypes and proportions of live progeny produced in a cross between a red-eyed, Notch female and a white-eyed male. This is an X-linked trait, so make sure to indicate the phenotypes of males and females.

Explanation / Answer

Let Xr be the genotype of red eye and Xw be the genotype of white eye. Let us denote the notch mutation by '

Genotype of female is XrXw' (red eyed). The female must be heterozygous. Deletion in Xw, white eye locus has resulted in notch.

Genotype of male is Xw, with white eyes (because male is not having the notch mutation.)

Cross is XrXw' X Xw

Result:- 1/2 males will be red eyed with genotype Xr. The rest half will die with genotype Xw'

1/2 females will be red eyed with genotype XrXw . The rest half females will be white eyed notched with genotype Xw'Xw

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