Gene linkage is the tendency of DNA sequences that are close together on a chromosome to be inherited together during the meiosis phase of sexual reproduction. Linked genes sit close together on a chromosome, making them likely to be inherited together. The closer two genes or sequences are to each other on a chromosome, the greater the probability that they will be inherited together. Conversely, genes that are farther away from each other are more likely to be separated during a process called homologous recombination.

A linkage map (also known as a genetic map) is a table for a species or experimental population that shows the position of its known genes or genetic markers relative to each other in terms of recombination frequency, rather than a specific physical distance along each chromosome. Linkage maps were first developed by Alfred Sturtevant, a student of Thomas Hunt Morgan. A linkage map is not a physical map or gene map.

Linkage analysis is a genetic method that searches for chromosomal segments that cosegregate with the ailment phenotype through families. It can be used to map genes for both binary and quantitative traits. Linkage analysis may be either parametric (if we know the relationship between phenotypic and genetic similarity) or non-parametric.

In general, organisms have a lot more genes than chromosomes. Thanks to the relationship between genes and chromosomes, we can use the frequency of recombination events between two genes (i.e., their degree of genetic linkage) to estimate their relative distance apart on the chromosome. Two very close-together genes will have very few recombination events and be tightly linked, while two genes that are slightly further apart will have more recombination events and be less tightly linked. By finding recombination frequencies for many gene pairs, we can make linkage maps that show the order and relative distances of the genes on the chromosome.

In summary, gene linkage refers to the tendency of DNA sequences that are close together on a chromosome to be inherited together during the meiosis phase of sexual reproduction. Linkage maps show the position of known genes or genetic markers relative to each other in terms of recombination frequency. Linkage analysis is a genetic method that searches for chromosomal segments that cosegregate with the ailment phenotype through families.