Summary

Throughout the mid 20th century, scientist Victor McKusick studied "the links between genetics and human diseases" (259). By the mid-1980s, McKusick had cataloged thousands of genes linked with diseases in humans and by 1998, he had discovered 12,000 "gene variants linked to traits and disorders, some mild and some life threatening" (261). They cataloged both "monogenic" or single-gene diseases as well as "polygenic" syndromes which are "caused by the convergent influence of multiple genes" (261). In the case of many prevalent chronic illnesses, such as hypertension or diabetes, they are under the influence of hundreds of genes and whether or not they manifest in an individual is highly dependent on environmental variables.

McKusick's work made four important conclusions: 1) mutations in a single gene can cause diverse manifestations in the body; 2) multiple genes could influence a single aspect of physiology; 3) even if a...