The homoeologous relationships of the arms of wheat chromosomes 2A and 2D to chromosome 2B and their effect on homoeologous pairing.

Homoeologous relationships between the arms of wheat group 2 chromosomes were analysed by studying homoeologous pairing in wheat-rye hybrids. Chromosomes 2A and 2D were identified using telocentrics 2AS, 2DS or 2DL. The remaining wheat chromosomes and their arms were identified by C-banding. Wheat chromosomes in the hybrids were derived from plants which were heterozygous (Ph1/ph1b) and monotelocentric for 2AS, 2DS or 2DL. In these plants, chromosome 2B and the telocentric showed regular bivalent pairing. From the results of homoeologous pairing in wheat-rye hybrids, normal homoeologous relationships between 2AS, 2BS and 2DS, as well as between 2AL, 2BL and 2DL, were deduced. There was no evidence that wheat group 2 chromosomes were involved in evolutionary chromosome rearrangements. The existence of a pairing promoter gene on chromosome arm 2DS was supported.