Differential distribution of aneuploidy in human gametes according to their sex.

The cytogenetic study of human gametes is a new and important source of information because most chromosomal abnormalities originate from meiotic disorders. The frequency and type of abnormalities were analysed in both spermatozoa and mature oocytes. A total of 13,975 human sperm chromosome complements and 1897 oocyte chromosome complements were analysed. In the present study, pooled cytogenetic data on human gametes have been examined to determine and compare the distribution of non-disjunctions in male and female gametes. Human spermatozoa are characterized by a significant excess of hypohaploidy and an equal distribution of aneuploidies among all chromosome groups, whereas mature oocytes display an equal ratio of hypohaploidy to hyperhaploidy and a high variability in the distribution of non-disjunction: in particular, there is a significant over-representation of aneuploidies in both D and G chromosome groups. This indicates that non-disjunction is not a random event in female meiosis and, consequently, that there are differences in the meiotic process between the sexes. Meiotic and environmental factors which could explain the non-random malsegregation of chromosomes in female meiosis are discussed. The role of maternal age as a cause of aneuploidy is questioned.