In Drosophila , the X-linked recessive mutation vermillion ( v ) causes maroon c
ID: 91693 • Letter: I
Question
In Drosophila, the X-linked recessive mutation vermillion (v) causes maroon colored eyes, in contrast to the bright red eyes of wild type. A separate autosomal recessive mutation, suppressor (s), causes flies to produce no eye pigmentation (white eyes) regardless of the vermillion genotype. You cross a true-breeding vermilion female with a true-breeding white-eyed male who is hemizygous (wild-type) for the vermillion gene.
A) What are the resulting F1 phenotypes for each sex?
B) What are the resulting F1 genotypes?
Explanation / Answer
In Drosophila, XX is female and XY is male.
Let vermilion allele be Xv (maroon red) and its dominant bright red allele be XV.
Let recessive suppressor (white) be w and its wild type be W.
True breeding vermilion female will have XvXv; WW genotype.
True breeding white male which is hemizygous for wild-type (bright red) gene male will have XVY; ww genotype.
The cross is between XvXv; WW and XVYww
XvXv; WW produces one kind of gamete which is XvW
XVYww produces two kinds of gametes. Those are XVw and Yw
So, ovum with XvW fertilize with either XVw or Yw spermatozoa.
We have two kinds of offsprings in equal proprtion.
One has XVXvWw genotype. It has two X chromosomes. So, it is female fly. Its phenotype is bright red eye.
The second one has XvYWw genotype. It is male fly. Its phenotype is maroon red eye.
Answers to questions:
a.
Male phenotype: maroon red eye
Female phenotype: bright red eye
b.
XVXvWw and XvYWw