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Three patients have been detected because of abnormal phenotypes. Balanced chromosome rearrangements were found in their karyotypes, and in one of the parents in each case. In these three families the association of an abnormal phenotype and a balanced chromosome rearrangement may either be a chance happening or be induced by a submicroscopic loss of chromosome material, for which different position effects may be responsible, according to the case in question. These observations prompt us to ask what decision should be made relative to termination of pregnancy if such a rearrangement is found in amniotic cells in a family with a previous abnormal child.

Chromosomal analysis of 100 second metaphases from 19 men attending an infertility clinic for various reasons was carried out to estimate the rate of non-disjunction occurring at first meiotic division. Second metaphases were selected on the basis of the good spread of their chromosomes. Karyotypes were performed using the relative length of the chromosomes and the centromeric index. Among aneuploid cells, only those containing a hyperhaploid complement (24) were regarded as informative. Of the 100 MII cells, two were hyperhaploid. The frequency of aneuploid MII cells following non-disjunction at first meiotic division is compared to the rate of aneuploid spermatozoa observed after using fertilization of zona-free golden hamster eggs.