The three human male specific expressed gene families DAZ, RBM, and TSPY are known to be repetitively clustered in the Y-specific region of the human Y Chromosome (Chr). RBM and TSPY are Y-specifically conserved in simians, whereas DAZ cannot be detected on the Y chromosomes of New World monkeys. The proximity of SRY to the pseudoautosomal region (PAR) is highly conserved and thus most effectively stabilizes the pseudoautosomal boundary on the Y (PABY) in simians. In contrast, the non-recombining part of the Y Chrs, including DAZ, RBM, and TSPY, was exposed to species-specific amplifications, diversifications, and rearrangements. Evolutionary fast fixation of any of these variations was possible as long as they did not interfere with male fertility.

Twenty-five specimens of lowland gorilla, including 24 specimens of the western lowland gorilla (Gorilla gorilla gorilla) and 1 specimen of the eastern lowland gorilla (G. gorilla graueri), were investigated by fluorescence in situ hybridization with a human-derived 18S + 28S rDNA probe. Specific hybridization was constitutively seen on the short arms of gorilla acrocentric chromosome pairs 22 and 23, corresponding to human pairs 21 and 22. Only one specimen of western lowland gorilla investigated showed an additional hybridization site at the telomeric short arm of one chromosome 1. From our own results and those in the literature, it is clear that the additional rDNA site on chromosome 1 must be regarded as a rare polymorphism in the subspecies of western lowland gorilla, possibly going back to a founder translocation event.

Several genes located within or proximal to the human PAR in Xp22 have homologues on the Y chromosome and escape, or partly escape, inactivation. To study the evolution of Xp22 genes and their Y homologues, we applied multicolour fluorescence in situ hybridization (FISH) to comparatively map DNA probes for the genes ANT3, XG, ARSD, ARSE (CDPX), PRK, STS, KAL and AMEL to prometaphase chromosomes of the human species and hominoid apes. We demonstrate that the genes residing proximal to the PAR have a highly conserved order on the higher primate X chromosomes but show considerable rearrangements on the Y chromosomes of hominoids. These rearrangements cannot be traced back to a simple model involving only a single or a few evolutionary events. The linear instability of the Y chromosomes gives some insight into the evolutionary isolation of large parts of the Y chromosomes and thus might reflect the isolated evolutionary history of the primate species over millions of years.