Recombination in the pseudoautosomal region in a 47,XYY male

Males with a 47,XYY karyotype generally have chromosomally normal children, despite the high theoretical risk of aneuploidy. Studies of sperm karyotyp es or FISH analysis of sperm have demonstrated that the majority of sperm a re chromosomally normal in 47,XYY men. There have been a number of meiotic studies of XYY males attempting to determine whether the additional Y chrom osome is eliminated during spermatogenesis, with conflicting results regard ing the pairing of the sex chromosomes and the presence of an additional Y. We analyzed recombination in the pseudoautosomal region of the XY bivalent to determine whether this is perturbed in a 47,XYY male. A recombination f requency similar to normal 46,XY men would indicate normal pairing within t he XY bivalent, whereas a significantly altered frequency would suggest oth er types of pairing such as a YY bivalent or an XYY trivalent. Two DNA mark ers, STS/STS pseudogene and DXYS 15, were typed in sperm from a heterozygou s 47,XYY male. Individual sperm (23,X or Y) were isolated into PCR tubes us ing a FACStar(Plus) flow cytometer. Hemi-nested PCR analysis of the two DNA markers was performed to determine the frequency of recombination. A total of 108 sperm was typed with a 38% recombination frequency between the two DNA markers. This is very similar to the frequency of 38.3% that we have ob served in 329 sperm from a normal 46,XY male. Thus our results suggest that XY pairing and recombination occur normally in this 47,XYY male. This coul d occur by the production of an XY bivalent and Y univalent (which is then lost in most cells) or by loss of the additional Y chromosome in some primi tive germ cells or spermatogonia and a proliferative advantage of the norma l XY cells.