Loss of the Y chromosomal PAR2-region in four familial cases of satellitedY chromosomes (Yqs)

Applying fluorescence in-situ hybridization (FISH) of various Y chromosomal DNA probes to four familial cases of human Yqs, it was possible to demonst rate that the formation of Yqs must have arisen from a reciprocal transloca tion involving the short arm of an acrocentric autosome and the heterochrom atin of the long arm of the Y chromosome (Yqh). Breakpoints map within Yqh and the proximal short arm of an acrocentric autosome resulting in the gain of a nucleolus organizer region (NOR) including the telomere repeat (TTAGG G)(n) combined with the loss of the pseudoautosomal region 2 (PAR2) at the long arm of the recipient Y chromosome. In no case could the reciprocal pro duct of an acrocentric autosome with loss of the NOR and gain of PAR2 be de tected. Using the 15p-specific classical satellite-III probe D15Z1 in two o f the four Yqs probands presented here, it could be shown that the satellit ed material originated from the short arm of chromosome 15. In contrast to the loss of PAR2 in Yqs chromosomes, another Y chromosomal variant (Yqh-) s howing deletion of long-arm heterochromatin in Yq12 has retained PAR2 refer ring to an interstitial deletion of Yq heterochromatin in such deleted Y ch romosomes.