The type of bristles in Drosophila are determined by recessive X-linked traits.

Question

The type of bristles in Drosophila are determined by recessive X-linked traits. The Xf allele encodes for forked bristles and is recessive to the normal bristles allele X+. Additionally, the autosomal red eye allele (b+) is dominant to the brown eye allele (b). If a homozygous female fly with normal bristles and wild type eyes is crossed with a male with forked bristles and brown eyes, they produce the F1 generation. Intercrossing of the F1 generation produces the F2 generation. Please give the phenotypes and proportions of the F2 generation.

Explanation / Answer

According to the question

a homozygous female fly with normal bristles and wild type eyes( X+X+b+b+) is crossed with a male with forked bristles and brown eyes(XfXf bb)

  X+X+b+b+ XfXf bb P

X+X b+b b+b+F1

Intercrossing between F1 by punnet square

so the results are

phenotypic characters - normal bristal with red eye : normal bristal with brown eye : forked bristal red eye : forked bristal with brown eye

phenotypic ration - 9 :3 :3 :1

X+b+ X+b Xf b+ Xf b X+ b+ X+X+ b+b+ X+X+ b+b X+Xf b+b+ X+Xf b+b X+ b X+X+b+b X+X+bb X+Xf b+b X+Xf bb Xf b+ X+Xf b+b+ X+Xf b+b XfXf b+b+ XfXf b+b Xf b X+Xf b+b X+Xf bb XfXf b+b XfXf bb

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