linkage /ling″kij/ [Gk, linke, connection] , 1. (in genetics) the location of two or more genes on the same chromosome so that they do not segregate independently during meiosis but tend to be transmitted together as a unit. The closer the loci of the genes, the more likely they are to be inherited as a group and associated with a specific trait, whereas the farther apart they are, the greater the chance that they will be separated by crossing over and carried on homologous chromosomes. The concept of linkage, which opposes the independent assortment theory of mendelian genetics, led to the foundation of the modern chromosome theory of genetics. See also synteny. 2. (in psychology) the association between a stimulus and the response it elicits. 3. (in chemistry) the bond between two atoms in a chemical compound or the lines used to designate valency connections between the atoms in structural formulas.
