The Assimilation of Classical Genetics into Human Genetics

Abstract

The major findings of classical genetics were worked out between 1900 and 1920. Although those interested in human heredity knew of these findings, the techniques used in fruit flies or maize were not possible for humans, and thus, there was a delay of several decades for most of these findings to be demonstrated in humans. What turned out to be a surprise was the way human (and other mammals) differed in their mechanisms and outcomes. For sex determination, the Y was male determining in humans but not in fruit flies. For nondisjunction, the sexual outcomes differed for conditions like XXY (fertile females in fruit flies but Klinefelter sterile males in humans). This was also true for several other classical genetic applications in humans which illustrated the difficulty of finding ways to replicate laboratory findings in humans. Victor McKusick assimilated these findings in his classic publication, Mendelian Inheritance in Man, the most valuable sourcebook for the literature and commentary on any human inherited disorder. The molecularization of genetics after 1990 made it easier for mapping, the analysis of multiple allelic series, and identifying lesions in mutant genes, but major differences still exist between human and medical genetics when these are compared to fruit fly or maize genetics.