In Drosophila, the gene for white (w) eyes is on the X chromosome and it is epis
ID: 302673 • Letter: I
Question
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.
Explanation / Answer
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
p1= ww and w+
p2= ww, w+, ww and w+
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+ ++ ++