Linkage refers to the physical association of genes on a chromosome. When genes are located on the same chromosome, they tend to be inherited together, and their F2 ratio deviates significantly from the expected 9:3:3:1 ratio for independent assortment. Recombination describes the generation of non-parental gene combinations. This occurs when genes on the same chromosome are exchanged during meiosis. The frequency of recombination depends on the distance between the genes: • Tightly linked genes show very low recombination (e.g., 1.3% for white and yellow genes). • Loosely linked genes show higher recombination (e.g., 37.2% for miniature wing gene). Alfred Sturtevant used the frequency of recombination between gene pairs on the same chromosome as a measure of the distance between genes, allowing him to map their positions on the chromosome.