Reciprocal translocations between acrocentrics: segregational analysis in twenty-nine families with unbalanced...

This study comprises 29 families with 42 unbalanced offspring in which reciprocal interacrocentric translocations (RIATs) were identified by banding. The observed unbalances were due to adjacent-1 (42.9%), adjacent-2 (28.6%) and 3:1 (28.6%) segregations. The concordance between the observed and expected segregations was 85.7% according to the Jalbert et al. (1980) criteria. 17.2% of the RIATs led to unbalances by 2 different segregations. 78.6% of the cases were maternal in origin. The overall incidence of spontaneous abortion was 37%. Corrected recurrence risks of unbalanced liveborn offspring for female and male carriers were seemingly similar: 17.8% and 12.5% respectively. These data indicate that RIATS exhibit (as distinctive features) an approximate 4:3:3 ratio for adjacent-1, adjacent-2 and 3:1 segregations, and a proneness to produce unbalances by different segregations.