RESUMEN
In situ hybridisation technology provides a new tool for chromosome analysis of human spermatozoa. We have used dual-colour fluorescence in situ with probes specific for the X and Y chromosomes and chromosomes 1 and 12 to (a) identify the primary male gametic sex chromosome ratio; (b) assess the number of numerical sex chromosome abnormalities, and (c) quantify the incidence of diploid sperm. We have examined over 60,000 sperm from three normal males and found the primary sex ratio to be indistinguishable from unity. The frequency of hyperhaploid sperm was 0.8, 1.03 and 2.27 per thousand for XX, YY and XY respectively, whilst 1.67 per thousand sperm were diploid. A comparison of our results with estimates of sex chromosome aneuploidy in human populations suggests that sperm carrying two sex chromosomes may be at a selective disadvantage.