Mapping of testis-determining locus on Yp by the molecular genetic analysis of XX males and XY females.

Sex reversal in males with female karyotypes is likely to be caused by the presence of cytogenetically undetectable Y-chromosomal DNA sequences that include the testis-determining gene(s). Studying a total of sixteen 46,XX males and one 47,XXX male, we detected Y-chromosomal DNA in 13 of the XX males (i.e. 80%) and in the 47,XXX male. The amount of Y-chromosomal DNA present in the patients varied between individuals. This allowed the construction of a molecular map of the Y-chromosome short arm. The putative testis-determining locus was assigned to the more distal portion of Yp, yet proximal to the pseudoautosomal region. Mapping of the testis-determining locus was complemented by molecular findings in 46,XY females. These individuals may carry microdeletions of the portion of Yp that appears to be required for normal male gonadogenesis. The deletions detected in 46,XY females always included those Y-chromosomal DNA sequences that were found in most 46,XX males. Furthermore, the same DNA sequences were missing in a female with a 46,X,dic(Y) karyotype. The observations suggest that some of our DNA probes hybridize with Y-chromosomal DNA sequences within a few million base pairs of the testis locus. Chromosome walking and pulsed-field gel electrophoresis investigations have been initiated in order to isolate those Y-chromosomal DNA sequences that are required for normal testicular development.