Linkage is concerned with the tendency of genes that are situated close to one another within the same chromosome to be inherited from the same parent. For a pair of genes, the recombination probability, p, is defined as the probability that the genes have been inherited from different parents. If p is much less than ½ then the genes are said to display linkage. Low values of p occur when the genes are situated close to one another within the same chromosome: this fact helps in deciding where genes are located within a chromosome.
A measure of linkage is the lod score, Z. In the simple case where the data consist of n independent observations on a particular pair of genes, of which r are recombinants, the lod score is
A lod score of 3 or more is generally held to provide evidence of linkage.
Another name for link (def. 2).
The tendency for two different genes on the same chromosome to remain together during the separation of homologous chromosomes at meiosis. Linkage can be broken by crossing over or by a chromosome mutation, when sections of chromosomes are exchanged and new combinations of genes are produced. See also haplotype; sex linkage.
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