Bivalent pairing in the tetraploid oat A. barbata, the main tetraploid form of A. strigosa polyploid complex, was found to be determined by a single recessive gene in quadriplex condition. This gene segregated in tetrasomic fashion in the A. barbata × A. strigosa autopolyploid, which indicates conspicuously autopolyploid origin of A. barbata and close relationships between the two chromosome sets of this oat, and the chromosomes of the diploid oat A. strigosa. It was speculated that the gene affecting bivalent pairing in A. barbata was evolved already at the diploid level in one of the A. strigosa races and had been recovered in quadriplex state following polyploidization of an intervarietal A. strigosa hybrid.