Linkage is a genetic mapping technique that identifies regions of chromosomes that are likely to contain a risk gene. They also rule out chromosome areas where there is a low chance of finding a risk gene.   Linkage studies show an association between two or more genes where the traits they control tend to be inherited together. This type of study pinpoints the chromosomal location of a gene that causes the manifested trait.  As stated before, researchers have not yet found a specific gene for the susceptibility of bipolar disorder.  Although, they have found some genes that have potential for it.
    "Linkage studies have defined at least six potential BPD susceptibility loci which meet suggested guidelines for initial identification and subsequent confirmation.  These loci, found on 18p11, 18q22, 21q21, 4p16, 12q24, and 22q11, are targets for BPD candidate gene investigations." (Berrettini, W. H., 2001)  Literature shows there has been some research conducted on many different chromosomes such as on chromosome 11, 15, and 22 but the strongest evidence for genetic linkage in bipolar disorder is to chromosome 18, because there are several positive studies from independent research groups (as cited by Millon, Blaney, & Davis, 1999)

**To see a presentation of a linkage study by Wade Berrettini go here-->Linkage Study by Berrettini **

**Some of the terms used in genetics are hard to understand so here is a helpful glossary that defines genetic terms  Genetic Glossary **