Aneuploidy was studied in populations selected for high seed-set with regular meiosis and low-seedset with irregular meiosis and an unselected population of the same origin. The frequency of aneuploids was significantly reduced in the high population that was characterised by increased bivalent frequency. In spite of a similar quadrivalent frequency in euploid plants of the low and the unselected population, the former population had a significantly higher frequency of aneuploids. However, there was no significant difference in the performance of aneuploid plants from the three populations. The results indicated that hyperaneuploid gametes were less functional than hypoaneuploid gametes but no significant difference was found in the performance of hypo- and hyperancuploids.