In the fruit fly, Drosophila melanogaster, wild type female fly is mated to a ma

Question

In the fruit fly, Drosophila melanogaster, wild type female fly is mated to a male with the three autosomal recessive traits scarlet (red body, ss), long (long body, ll) and hairless (no thoracic bristles, hh). Phenotypically wild-type F_1 female progeny were mated to fully homozygous (mutant) males. If the genes were completely unlinked, what phenotypes in what ratios would you observe? The following (1000) total were observed. Draw a genetic map showing the gene order and between gene pairs. Phenotypes Observed long, wt, hairless 396 wt, scarlet, wt 422 long, wt, wt 35 long, scarlet, hairless 42 wt, scarlet, hairless 41 wt, wt, hairless 9 long, scarlet, wt 12 wt, wt, wt 43 1000 Calculate the interference.

Explanation / Answer

Parental h l +

              + + s

SCO for h and l = 35+41+9+12 = 97 = 97/1000 = 9.7%

SCO for s and l = 42+43+9+12 = 106 = 106/1000 = 10.6%

DCO for h and s = 35+41+42+43 = 161 = 161/1000 = 16.1%

            h------------l----------------------s

                       9.7          10.6

Inteference DCO - 9.7 and 10.6

          0.097*0.106 = 0.010

Total events = 0.010*1000 = 10 times    DCO expected 10 But actual DCO in experiment = 9+12=21

       Coeff of coincidence = 21/10 = 2.1

        I = 1-2.1 = -1.1 Negative inteference

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