A true-breeding mutant strain of Drosophila has brown-colored eyes. When males o

Question

A true-breeding mutant strain of Drosophila has brown-colored eyes. When males of this strain are mated to wild type Drosophila females with red colored eyes, all of the Fl offspring have red eyes. When the Fl males and females are mated, they produce red- and brown-eyed offspring in a 3:1 ratio. A reciprocal cross of brown-eyed parent females with red-eyed parent males produces Fl and F2 offspring with the same phenotypic ratios as the first cross.

a. Is the brown eye mutation dominant or recessive with respect to the wild type allele for eye color? Briefly explain.

b. Is the eye color gene located on an autosome or a sex chromosome? Briefly explain.

c. Using the format for naming mutant and wild type alleles of Drosophila genes assign allele designations and write out the genotypes for the cross of the brown-eyed males and red-eyed females and their F1 offspring.

d. If the F1 males and females in 1c are crossed to each other, what are the genotypes of their F2 offspring?

Explanation / Answer

Answer--

a) When the Fl males and females are mated, they produce red- and brown-eyed offspring in a 3:1 ratio. so it is the case of Complete Dominance.So the brown eye mutation is recessive with respect to the wild type allele for eye color.

b) eye color gene is always located on an autosome or non-sex chromosome. A gene on non-sex chromosome is always expressed. In case of heterozygote, the gene mutation always refers to a gene on one of the pairs of autosome.

C) Let consider, B= Brown Colored eye allele
   R= Wild Red colored eye allele

so the all F1 offsprings are RB.

and the genotypes of F2 generation are RR, RB, RB and BB.

d) the genotypes of their F2 offsprings are RB,RB,RB,RB.

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