Question

Cinnabar eyes (ci), curved wings (cw) and smooth abdomen (sa) are all genes linked in the order given on chromosome II of Drosophila. The three mutant alleles are all recessive to the wild-type alleles (ci+ wild type eyes; cw+ straight wings; sa+ normal abdomen). A female heterozygous for the mutant alleles at each locus is crossed to a homozygous recessive male (ci cw sa/ci cw sa). They have the following progeny:

Phenotype                                                                        Number

Cinnabar eyes, straight wings, normal abdomen                    300

Wild type eyes, straight wings, normal abdomen                   50

Cinnabar eyes, curved wings, smooth abdomen                     45

Cinnabar eyes, curved wings, normal abdomen                       10

Wild-type eyes, curved wings, normal abdomen                    150

Wild-type eyes, curved wings, smooth abdomen                   308

Cinnabar eyes, straight wings, smooth abdomen                    125

Wild-type eyes, straight wings, smooth abdomen                  12

Total                                                                                    1000

Draw the two chromosomes of the heterozygous female parent showing the linkage of the mutant and wild-type alleles for each of the three genes (i.e., which alleles were linked on each the heterozygous female’s two copies of chromosome II?)

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Answer 1

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