ou are experimenting with the mutation in fruit flies that causes the white eye

Question

ou are experimenting with the mutation in fruit flies that causes the white eye phenotype. You are predicting this gene is recessive and linked on the X chromosome. If you have a P generation that consists of a male with white eyes and mate this with a female that has red eyes. The F1 generation all have red eyes. These F1 flies are allowed to mate with each other and you collect the offspring. If you collect 60 male flies, how many of these males would you predict have white eyes? Enter an expected number of male flies, not a percentage. Assume equal survival of red- and white-eye fly embryos.

Explanation / Answer

In Drosophila white eye is an X linked recessive trait and red eye is an X linked dominant trait. Allele XW codes for the white eye and allele Xw+ codes for red eye.Therefore-

white eyed male x red eyed female

XwY x Xw+Xw+

F1 - ALL RED EYED MALES AND FEMALES

Xw+Y X Xw+Xw

XwY -25% white-eyed male.

,Xw+Xw, Xw+Xw+, Xw+Y -75%red eyed females and males(3:1)

Because white-eyed males are 25%. Therefore 25% of 60 are whte eyed males

i.e 25 /100 x 60 = 15 males will be white eyed.

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