1) In fruit flies, eye color is x linked recessive - R= red eyes and r=white eye

Question

1) In fruit flies, eye color is x linked recessive - R= red eyes and r=white eyes. Body color is autosomal - B= brown body and b= yellow body. What phenotypic ratios do you expect in a cross of a white eyed male who is homozygous recessive for body color and a red-eyed (carrier) female who is a heterozygote for body color?

2) In fruit flies, eye color is x linked recessive - R= red eyes and r=white eyes. Body color is autosomal - B= brown body and b= yellow body. What phenotypic ratios do you expect in a cross of a red eyed male who is homozygous recessive for body color and a red-eyed (carrier) female who is heterzygous for body color?

Explanation / Answer

,The genotypes :

XR - x linked gene for red eyes, Xr - x linked gene for white eyes.

B - autosomal(sex independent) gene for the brown body,    b - autosomal gene for the yellow body,

Possible genotypes for Red eyes - XRXR , XRXr , XR Y

Possible genotypes for white eyes - XrXr , XrY

Possible genotypes for the brown body - BB.Bb

Possible genotypes for the yellow body - bb

In all of the tables, the male gametes are in rows and female gametes in the columns.

Female - XX, Males - XY

(1) white-eyed male x red-eyed carrier female

Phenotypic ratio = red : white = 2 : 2 = 1 : 1

Homozygous recessive male x Heterozygous female

Phenotypic ratio = brown : yellow = 2 : 2 = 1 : 1

(2) red-eyed male x red-eyed carrier female

Phenotypic ratio = red : white = 3 : 1

Homozygous recessive male x Heterozygous female

Phenotypic ratio = brown : yellow = 2 : 2 = 1 : 1

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