Genetic linkage refers to co-segregation of alleles of two different loci in families due to their physical proximity on a chromosome. If two loci reside very close on the same chromosome, they are unlikely to be segregated during the meiosis and will be transmitted together to the offspring. Thus, a linkage study is in essence an analysis of co-segregation of two loci in families, one of which is observed “marker” with known location on the chromosome, and the other is a latent locus containing a genetic variant underlying a phenotype of interest such as a disease. If a certain marker co-segregates with the phenotype, it can be inferred that a gene contributing to this phenotype is located in the same chromosomal region as the marker. Linkage analysis can provide the chromosomal location of the putative gene with a certain degree of confidence and resolution, but the identification of the gene requires further efforts such as DNA sequencing. Linkage studies are now becoming rare, as they are being surpassed by association studies.
