It appears that the gene for wing type and body color are on the same chromosome. The only explanation that could explain what had happened is a phenomena called crossing over. Crossing over is a random process that occurs during prophase I of meiosis. It occurs in the tetrads when pieces of two homologous chromosomes switch places with each other. The new chromosomal set up is different from the original homologs found in the cell before prophase I began.
Geneticists can use recombination data to map a chromosomes genetic loci.
A genetic map can be constructed from the crossing over data. This map is called a linkage map. Let us look at an example of how this process works. A test cross must be conducted in order to demonstrate the process of crossing over. A test cross is the mating of a heterozygous fly for both characteristics with a homozygous recessive fly for both characteristics.