Gene Mapping Principles and Practice Problems illustrating recombination frequencies between genes on a chromosome.

- The image presents a gene mapping problem involving three genes on a chromosome: b (black body), cn (cinnabar eyes), and vg (vestigial wings).
- Recombination frequencies are given: 17% between b and vg, 9% between b and cn, and 9.5% between cn and vg.
- To determine gene order, note that the largest recombination frequency (17%) must span the outermost genes, so b and vg are at the ends.
- Since the sum of the smaller distances (9% + 9.5% = 18.5%) is close to 17%, there may be slight measurement error or double crossover effects, but the most likely order is b — cn — vg.
- The 9% distance is between b and cn, and 9.5% between cn and vg, confirming cn is in the middle.
- Thus, the correct gene order is b — cn — vg, with map distances of 9 cM between b and cn, and 9.5 cM between cn and vg.