Segregation of sex chromosomes in human lymphocytes.

Centromeric FISH was used to investigate the segregation of sex chromosomes in human lymphocytes. The aim of the study was to evaluate the effects of cell culture, cytokinesis block, age and sex on segregation and to compare the behaviour of the X and Y chromosomes. In uncultured T lymphocytes of five elderly women, the mean frequencies of nuclei hyperdiploid and hypodiploid for the X chromosome were not significantly affected by culturing the cells or by cytokinesis block. In cultured binucleate lymphocytes of two age groups of men, the X chromosome showed significantly higher mean frequencies of hyperdiploidy, hypodiploidy and reciprocal gain and loss than the Y chromosome. Reciprocal gain and loss of the Y chromosome was statistically significantly higher in the older than the younger men. In four women, studied in the same series, the rates of X chromosome aneuploidy did not significantly differ from those obtained in men. In conclusion, malsegregation of the X chromosome is common in lymphocytes of both men and women and more frequent than Y chromosome malsegregation. However, there is no clear sex difference for X chromosome reciprocal gain and loss. This would suggest that the high loss of the X chromosome in women, documented in metaphase studies, is due to micronucleation.