22) (0 points) In Drosophila melanogaster, black body recessive to normal color

Question

22) (0 points) In Drosophila melanogaster, black body recessive to normal color (b purple eyes (pr (b) is are recessive to red eyes (pr and vestigial wings (vg) is recessive to normal wings (vg A female fly with a black body, purple eyes and vestigial wings is crossed to a wild type male. The F1 females produced by this cross were mated with black, purple and vestigial males in a testcross. The progeny resulting from the testcross are listed below. vg b pr 475 vg b pr vg b+ pr 87 vg b t pr 472 b pr 20 vg b pr+ 89 vg b+ pr 21 vg bt pr 7 Total a. Determine order of these genes on the chromosome. b. Calculate the map distances between the genes. among these genes. c. Determine the coefficient of coincidence and the interference

Explanation / Answer

Answer:

a. The non-recombinants are: vg+ b+ pr+ and vg b pr.

The double crossovers are: vg+ b pr and vg b+ pr+.

Comparing the two, we see that they differ only at the vg locus, so vg must be the middle gene.

b. vg+ b+ distance: Recombinants are: vg+ b, vg b+

R.F = (21 + 20 + 6 + 7) / 1177 = 54/1177 = 0.0458 = 0.046 = 4.6% = 4.6 m.u.

vg+ pr+ distance: Recombinants are: vg+ pr, vg pr+

R.F = (87 + 89 + 6 + 7) / 1177 = 189/1177 = 0.16 = 16% = 16 m.u.

The b+ - pr+ distance is the sum of these two distances: 4.6 + 16 = 20.6 m.u.l.

c. Expected DCOs = RF1 × RF2 × Number of total progeny =0.046 * (0.16) * (1177) = 8.66

C.O.C. = observed DCOs/expected DCOs = (6+7)/8.66 = 13/8.66 = 1.5

Interference = 1 – C.O.C = 1-1.5 = -0.5

Negative interference is the phenomenon whereby a crossover in a particular region enhances the occurrence of other apparent crossovers in the same region of the chromosome.

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