Campbell Problem 5

Molecular Genetics Problem 5

5. In another cross, a wild-type fruit fly (heterozygous for gray body color and red eyes) was mated with a black fruit fly with purple eyes. The offspring were as follows: wild-type, 721; black-purple, 751; gray-purple, 49; black-red, 45. (a) What is the recombination frequency between these genes for body color and eye color? (b) Following up on this problem and problem 4, what fruit flies (genotypes and phenotypes) would you mate to determine the sequence of the body color, wing shape, and eye color genes on the chromosomes?


To help see the process write out the genotypes. The genes can be symbolized as follows:

b+ = gray body b = black body pr+= red eyes pr = purple eyes

Genotype of the heterozygous wild type (gray body and red eyes) using Morgan’s method:

The genotype of the homozygous recessive individual (used in a testcross) would be:

Determine the recombination frequency:

721 wild-type (gray-red) 721/1566 = 46% expected
751 black-purple 751/1566 = 48%

49 gray-purple 49/1566 = 3% recombinant
45 black-red 45/1566 = 3% recombinant

Total flies = 1566


(a) The percent recombination is therefore 6%


(b) Example: cross a wild type fly heterozygous for body color and wing shape with a fly homozygous recessive for the same traits (black body/curly wings)