Method for Identifying the Region of the Y-chromosome Containing the Testis Determining Factor in Humans
DNA specific for the Y chromosome can be isolated from recombinant DNA libraries made from male cells by screening DNA prepared from XX and XY cells. Y-specific sequences will bind only to DNA prepared from XY cells but not from XX cells (Figure 1). By screening such Y-specific sequences on DNA from individuals missing parts of the Y chromosome, one can determine the portion of the Y chromosome from which that particular sequence is derived (Page, 1986).
In the human population, there exist both XX males (about 1 out of every 20,000 males) and XY females. The DNA hybridization results (Page et al., 1985; Vergnaud et al., 1986) demonstrated that XX males had Y-specific DNA from Y chromosome region 1 translocated onto one of their chromosomes. Moreover, all the XY females tested were missing this region of the Y chromosome (Figure 2). It seems most likely, then, that the gene for the testis-determining factor maps to region 1 of the Y chromosome, near the tip of the short arm. Similar evidence from mice also suggested that this region of DNA contains the testis-determining gene of the Y chromosome (Singh and Jones, 1982; Eicher et al., 1983).
In 1990, Sinclair and colleagues narrowed the region to a 35,000 base-pair domain of the small arm of the Y chromosome. A history of this winnowing process is seen in Figure 3.
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