ALPHOIDLESS CENTROMERE OF A FAMILIAL UNSTABLE INVERTED Y-CHROMOSOME

We report on a 3-generation pedigree in which an inverted unstable Y c hromosome had no phenotypical or reproductive repercussion despite a s izeable proportion of secondary aneuploidies (mainly 45, X cells) in l ymphocytes. This chromosome was metacentric and had a single Cd-positi ve primary constriction, but occasionally assumed a normal acrocentric aspect. FISH using the probe DYZ3 revealed a single strong signal; un expectedly, the signal was outside the primary constriction and appear ed to map in the middle of p, that is, at the usual centromeric locali sation. Therefore, this chromosome should be regarded as a remarkable pseudodicentric because the major alphoid array tvas located at the in active centromere but not at the active one. This chromosome may have resulted from a) a transcentric inversion with the 48 bp satellite arr ay of proximal Yq being relocated next to the Yq heterochromatin, or b ) an intrachromosomal insertion of nonalphoid centromeric sequences.