Ineffectivity of accessory bisatellited marker chromosomes in inducing meiotic nondisjunction.

It has been postulated that accessory marker chromosomes, which frequently show satellites, are effective in inducing meiotic nondisjunction in the carrier. This hypothesis has been tested by comparing expectations derived from it with actual data. Due to the discrepancies between these expectations and actual observations this hypothesis does not hold true: The frequency of trisomy 21 in the offspring of a carrier of an accessory bisatellited marker chromosome cannot be shown to be actually increased, and there is no increase of either the rate of miscarriages to such carriers or the frequency of an accessory marker chromosome among the individuals with regular trisomy 21. This indicates that the risk of trisomy in the offspring of a carrier of an accessory marker chromosome corresponds to the overall incidence of this trisomy.