In drosophula, the production of red eye pigment requires the autosomal dominant
ID: 318778 • Letter: I
Question
In drosophula, the production of red eye pigment requires the autosomal dominant allele, Bn. The dominant allele Ve of an X-linked gene allows production of the brown pigment, xanthomatin, and turns the pigmented eye purple, its recessive allele leaves bright red (vermillion). a fly producing no pigment has white eyes while VeVe; bnbn fly has brown eyes.
A. Give the expected phenotype (and ratios)
of flies of each sex in the F1 and the F2 generations from a cross of truebreeding brown females to truebreeding vermillion males.
B. Now give the expected phenotypes (ratios) of flies of each sex in the F1 and the F2 generations from a cross of truebreeding vermillion females to truebreeding brown males.
C. How are the results in B different from the results in A.
Explanation / Answer
A. since the female flies are pure bred brown and male flies are pure bred vermillion,
the genotypes would be XVe XVe bn bn
the males should be : Xve Y BN BN
therefore the F1 cross :
the expected phenotype would be : 2 female purple red eyes : 2 male purple red eyes.
ratio is 1:1
when we do a dihybrid cross, the ratio would be 9:3:3:1.
9 purple red eyes, 3 purple eyes, 3 red brown eyes, 1 white eyes .
B . the truebreeding vermillion females would be : Xve Xve Bn Bn
the truebreeding brown males should be : XVe Y bn bn
therefore the F1 cross :
2 brown eyes females : 2 red eye males
now when we cross them we would again get a ratio of 9:3:3:1
9 being brown eyed, 3 being red eyed, 3 being purple eyes, 1 being white eyes.
c. the results are different in B from A because both of them are reciprocal crosses in part a we cross brown females to vermillion males and in cross b we cross brown males to vermillion females.
XVebn XVebn XveBn XVeXveBnbn XVeXveBnbn YBn XVeYBnbn XVeYBnbnRelated Questions
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