A map of the yellow (y), white (w), and miniature (m) genes on the X chromosome of Drosophila melanogaster. Each number represents the percentage of recombinant offspring produced between two loci and is defined as the interlocus distance.

1% recombination between two genes on a chromosome is defined as 1 map unit (mu), or 1 centimorgan (cM). The interloci distances are additive.