DNase I hypersensitive sites along the XY bivalent at meiosis in man include the XpYp pairing region.

The DNase I nick translation technique has been applied to human meiotic chromosomes in situ. At metaphase I, distinct hot spots of autoradiographic labelling occur at three positions along the XY bivalent; over the Xpter and Ypter pairing tips, over Xq and Yq terminal/telomeric segments, and at a site just below the centromere in Xq. The latter might correspond to the postulated human inactivation centre. Compared with somatic chromosomes, human meiotic bivalents in general exhibit a greater accessibility to DNase I. Site-specific conformational changes in the DNA between somatic and germ line cells could be a necessary prerequisite for crossing-over.