Chromosome distribution studies in XXY karyotypes

The method of 'generalised distances' was applied to characterise the relative position of the metaphase chromosomes in a population of XXY subjects (180 metaphases from 28 subjects). The most striking observation was that the presence of an extra gonosome coincided with a disturbance of the normally stable centromere-centre distribution pattern. The distribution analysis gave no clear cut evidence for the induction of gonosomal trisomy XXY by chromosome association. No significant association was observed between X and X or X and Y but there was a smaller distance between X and Y in XXY karyotypes than in XY karyotypes. As far as autosomes are concerned, the XXY karyotypes were characterised by a less central location of the acrocentrics without a clear decrease of association frequencies of these acrocentrics, and the C heterochromatin rich chromosomes were more often associated than in the XX and XY control populations. These data do not support the idea that gonosomal trisomies result from chromosome associations, but favour the hypothesis that spindle degeneration as a result of intrafollicular ageing of C heterochromatin polymorphism may be responsible for non-disjunctions.