Question

In Drosophila, the gene for white (w) eyes is on the X chromosome and it is...

In Drosophila, the gene for white (w) eyes is on the X chromosome and it is epistatic over brown and scarlet.

White eyes can also result by crossing brown-eyed females (bw) with scarlet eyed males (st) (that is, when both mutant alleles are present).A cross is made between white-eyed females with the genotype w//w (otherwise, homozygous for wild type alleles) and white-eyed males hemizygous for the wild type allele (w+ ).

List the expected: a) Genotypes of the P1 and P2 flies.

b) F1 phenotypes and genotypes. 26

c) Expected F2 phenotypic ratios. Show your work.

CONCEPT PROBLEM 4 How can the same phenotype stem from many different genotypes? Explain.

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Answer #1

Q1- Genotype of p1 and p2

p1= ww and w+

p2= ww, w+, ww and w+

b) f1 phenotypes and genotypes

F1..

ww w+ ww w+

phenotypic ratio = genotypic ratio = 1:1

phenotype = white

c) expected f2 phenotypic ratios

ww = 36

w+ = 24

++ = 4

phenotypic ratio = 36:24:4

w w w w w w + +
w ww ww ww ww ww ww w+ w+
w ww ww ww ww ww ww w+ w+
w ww ww ww ww ww ww w+ w+
w ww ww ww ww ww ww w+ w+
w ww ww ww ww ww ww w+ w+
w ww ww ww ww ww ww w+ w+
+ w+ w+ w+ w+ w+ w+ ++ ++
+ w+ w+ w+ w+ w+ w+ ++ ++

p1= ww and w+

p2= ww, w+, ww and w+

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