When I am doing the Drosophila laboratory, IF I got the result of F1 below that:

Question

When I am doing the Drosophila laboratory, IF I got the result of F1 below that:

Wild males: 22 White eyed male :20

Wild female : 14 White eyed male:13

1 ) What ismy hypothesis to explain the phenotypes (white/red eye trait) observed in your F1 generation? (Punnett square may be used to explain).

In this, I got the percenage Rm :0.32 (32%) Wm:0.29(29%) Rf:0.2( 20%) Wf: 0.19 (19%)

2)Ifmmy hypothesis is correct, what will be the predicted ratio of phenotypes in your F2 generation? (Punnett square may be used to explain)

Explanation / Answer

1. Look at the F2 generation. There are 2 genotypes found in both sexes, so this is almost certainly autosomal. Now check the phenotypic ratio. There are 31 red-eyed flies and 13 sepia-eyed flies. Ratio is approx. 3:1 which is what you expect for autosomal. 2. In the F2 there are no white-eyed female flies, so this immediately suggests X-linkage (= sex linkage). Males only need to inherit 1 copy of an X-linked trait from their mother to express the trait, females need to inherit 2 copies, one from each parent to express it. F1 males were all red-eyed so passed on that allele to all their daughters, so this is what you would expect for an X-linked trait. You can also check sex ratio, this is 50:50, so it is not an autosomal recessive that kills females (probably too complicated for you to worry about. 3. Autosomal loci. This is easy to trace back. F2 is 1/4 ss, so both parents must have carried the s allele and the dominant red one S. F1 was therefore Ss x Ss giving offspring SS, Ss, sS and ss. Only way to guarantee all F1 were this genotype would be to cross an SS parent with an ss one, but you don't know which sex was which. X-linked locus. There were some F2 red males and some white - both got the X chromosome from their mothers, so F1 mothers must have been XWXw (where w is the white allele). Fathers in the F1 were all XWY as they passed on the red allele to their daughters. The F1 males inherited their XW from their mothers. As none were white P female must have been XWXW to pass the XW to all her sons. She would also have given XW to her daughers, therefore P male must have passed on the Xw allele to his daughters and his genotype was XwY.

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