linkage map

A linkage map is a diagram of where genes lie along a chromosome, ordered and spaced according to how often they are inherited together. It is, in effect, a map drawn entirely from family and breeding data rather than from looking at the DNA directly.

The logic is straightforward: genes that recombine rarely are placed close together, and genes that recombine often are placed far apart, with distances measured in centimorgans. By comparing the recombination frequencies of many pairs of genes, geneticists can work out their linear order and assemble a map of the whole chromosome.

Linkage maps were the first way scientists could position genes before DNA could be read, and they remain useful for tracking inherited traits and disease genes through families. The term is often used interchangeably with genetic map; both express distance in recombination units rather than in physical base pairs.