Abstract
The natural amphidiploid, Brassica juncea, has diploid-like meiotic behaviour. In three duplication-deficiency plants recovered from an interchange heterozygote stock, a large number of chromosomes were involved in multiple associations. It is suggested that this high level of pairing was due to the conjugation of homoeologous chromosomes and that the deficient segment carries a gene (genes) for suppressing such pairing and for maintaining balanced diploid-like behaviour.