Interchromosomal effect leading to an increase in aneuploidy in sperm nuclei in a man heterozygous for pericentric inversion (inv 9) and C-heterochromatin

We describe a man with pericentric inversion 9 and constitutive heterochrom atin, and a high disomy rate in his sperm cells (with all probes analyzed). The disomy rate was estimated with the following probes: 8, 9. 18, X, and Y, and was significantly higher than that in control sperm cells, while chr omosome 9 showed the highest disomy frequency. The probes of X and Y togeth er showed the same disomy frequency as X and Y alone, which indicates the s ame non disjunction rate in the first meiotic division. We suggest that the interchromosomal effect found in this man differed from other findings in sperm cells of men carrying an inversion in terms of the difference in the length of the heterochromatin between the two chromosomes 9. Also, it is we ll known that the effect of inversion 9 with increased heterochromatin is h ighly variable and may even vary in members of the same family.