Cooperation of selection and meiotic mechanisms in the production of imbalances in reciprocal translocations

We have used data from chromosomally unbalanced offspring observed at birth , as well as data from sperm chromosome analysis, to study the meiotic segr egation of reciprocal translocations. Using data from a total of 1,597 unba lanced children, we have observed an excess in maternal origin for all mode s of imbalance. This excess is particularly marked for the 3:1 unbalanced m ode, for which we have also observed a maternal age effect, indicating a cl ose relationship with autosomal trisomies. In addition, a statistical analy sis of data from 34 different published studies using sperm chromosome anal ysis has demonstrated that factors which, for reasons of viability, produce a predisposition for a particular mode of imbalance at birth also appear t o favor meiotic production of this type of imbalance. Thus the production o f unbalanced gametes of a particular type is influenced by the size of the imbalance. Copyright (C) 2000 S.Karger AG, Basel.