With the advances of molecular genetics technologies, it then became possible to scan the genome using a type of genetic variation called microsatellites. In this approach, called linkage analysis, the pattern of transmission of a disease (e.g., alcoholism) in families with multiple affected members is compared with the pattern of transmission of certain microsatellites (see figure 1B). The underlying hypothesis is that alcoholics within a family share many risk alleles; therefore, genes containing alleles that increase the risk for alcoholism reside within chromosomal regions that are inherited by most or all alcoholic family members. Unfortunately, however, the chromosomal regions that were identified using this approach often contained hundreds or even thousands of genes, making it very challenging to determine which specific gene(s) contribute to the risk for alcoholism.
