You design Drosophila crosses to provide recombination data for genes a, which is located on the chromosome shown in Figure 15.12. Gene a has recombination frequencies of 14% with the vestigial wing locus and 26% with the brown eye locus. Approximately where is a located along the chromosome?

The gene for the vestigial wing is located at 67.0 map units, and that of brown eyes is 104.5 map units from the aristae locus. Thus,the distance between these genes is the difference in their map units.

Thus, the distance between the two genes is 37.5 map units (104.5-67.0).

The recombination frequency of geneawith vestigial wing locus is 14%, and that of brown eye locus is 26%.The distance between the genes for the vestigial wing and brown eye is 37.5.

However, none of the gene frequencies is greater than 37.5%. This suggests that the gene a must be located between the vestigial wing locus and brown eye locus.

One percent recombination frequency corresponds to one map unit.The geneais located 14 map units right from the vestigial wing locus because the recombination frequency of geneawith vestigial wing locus is 14%.

Similarly, geneais located 26 map units left from the brown eye locus because the recombination frequency of geneawith brown eye locus is 26%. Thus,geneais 14 map units far from the vestigial wing locus, which is almost half the distance from the brown eye locus (26 map units).

This suggests that gene a is located one-third from the vestigial wing locus to the brown eye locus.