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 segregation of reciprocal translocations. Using data from a total of 1,597 unbalanced children, we have observed an excess in maternal origin for all modes of imbalance. This excess is particularly marked for the 3:1 unbalanced mode, for which we have also observed a maternal age effect, indicating a close relationship with autosomal trisomies. In addition, a statistical analysis of data from 34 different published studies using sperm chromosome analysis has demonstrated that factors which, for reasons of viability, produce a predisposition for a particular mode of imbalance at birth also appear to favor meiotic production of this type of imbalance. Thus the production of unbalanced gametes of a particular type is influenced by the size of the imbalance.