Cytogenetic and molecular analysis of a Yq isochromosome.

The dicentric Yq isochromosome of a male with azoospermia and some features of Klinefelter's syndrome was examined using cytogenetic and molecular methods. C- and R-banding of chromosomes of peripheral blood lymphocytes revealed a complex mosaic consisting of 46,X,i(Yq)/45,XO/46,XY/47,XYY/47,XY, i(Yq)/47,X,i(Yq),i(Yq) cells. EBV-transformed lymphocytes either had a 46,X,i(Yq) (90%) or a 46,X, + mar (10%) karyotype. The marker chromosome was shown to be Y-derived by in situ hybridization. C-banding, quinacrine- and DA/DAPI-staining indicated inactivation of one of the centromeres in almost all Yq isochromosomes. The use of Y chromosomal DNA sequences demonstrated that most of the Y chromosome, including its short arm, was duplicated.