Twenty years of human cytogenetics

Abstract

Human cytogenetics has undergone an immense development during the past twenty years. The number of human individuals karyotyped now amounts to some two million. The incidence of abnormal karyotypes may be estimated to 15% of all human zygotes, 50% of abortuses and 0.5% of unselected newborns. In contrast to the mouse, in which all fetuses with unbalanced translocation karyotypes nearly always die, many such individuals are live-horn in man. The study of sex chromosome aneuploidy revealed the role of the Y chromosome in sex determination and aided the discovery of the inactivation of one of the X chromosomes in female somatic cells. The chromosome handing techniques, first developed around 1970, improved enormously the resolution in structural chromosome identification. Only two phenomena, wholly new to cytogenetics, have been discovered during the period: centromeric inactivation and fragile chromosome sites. Other important developments have been the analysis of karyotypic evolution in neoplasms, chromosome responses to mutagenic agents and meiotic events related to male infertility. Looking forward, two areas of research seem especially urgent: chromosome studies in very early embryos and systematic registration on a world scale of karyotypes from prenatal diagnosis. Other promising areas include the organisation of the human genome, the H-Y antigen, and the ancient problem of meiosis.