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A mutation in the Drosophila bristle gene (fb) (which is X-chromosome linked) causes a recessive forked bristle phenotype (rather than the normal type of bristle). Another mutation in Drosophila autosomal body color gene (BR) causes a recessive brown color body (rather than the normal black body). A geneticist carried out the following cross:
X+ / Y ; BR/br x X+/ Xfb ; BR/br
If total of 240 F1 progeny were obtained, the “expected” numbers are: normal bristle male progeny - __________; forked bristle males - __________; normal bristle females - ___________; and forked bristle female - __________.
The geneticist actually obtained 240 males and among them 170 flies had black body and 70 had brown body. Does the result fit Mendelian segregation model (3:1)? Please filled the table below and use Chi-square test to determine it.
Chi-square = Σ [(obs-exp)2 / exp] = _______________
Reject or support
The ratio of the phenotype is 1:2:1 (normal male:normal female: affected male)
Since it is a X linked recessive trait, the mutation should be present in both the X chromosome in females to be able to determine a phenotypic change.
If total F1 progeny=240,
the “expected” numbers are:
normal bristle male progeny - 60
forked bristle males - 60
normal bristle females - 120
and forked bristle female - none
Null Hypothesis : The cross follows simple Mendelian ratio 3:1
Alternate Hypothesis : The cross follows some other ratio
Conclusion : Accept Null and reject Alternate Hypothesis
The cross follows simple mendelian ratio 3:1
A mutation in the Drosophila bristle gene (fb) (which is X-chromosome linked) causes a recessive forked...
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