Studies using this approach initially focused on understanding the genetic mechanisms underlying disorders that are caused by defects in a single gene and for which the inheritance pattern could be clearly specified. These studies involved statistical tests called parametric linkage analyses, which use DNA markers to locate, or map, a disease gene to a particular chromosomal region. Such analyses led to the identification of the genes causing Huntington’s disease, cystic fibrosis, Duchenne muscular dystrophy, and hundreds of other genetic disorders.1
