Homoeologous Meiotic Chromosome Pairing in Triticum aestivum in which Chromosome 5B is replaced by an Alien Homoeologue

Abstract

In the hexaploid bread wheat (Triticum aestivum 2n = 6x = 42) meiotic pairing is confined to fully homologous chromosome partners and inheritance is disomic. This arises from the activity of a single locus (Ph, pairing homoeologous) distally located on the long arm of chromosome 5B^1,2. In the absence of chromosome 5B, pairing and recombination take place between homoeologous chromosomes, which are genetically related members of the three component genomes, as well as between homologues³. Knowledge of the 5B system is of fundamental and practical significance. It throws light on the process of chromosome pairing during meiosis⁴, and assists in the interpretation of the cytogenetic behaviour of polyploid wheat, and indeed of all allopolyploids. Moreover, interference with its activity has been exploited to cause abnormal recombination between homoeologues in order to introduce into wheat chromosomes useful genes from chromosomes of related species⁵. Consequently to extend the understanding of the system, as well as to facilitate its use in breeding work, attempts are continually being made to isolate new wheat genotypes displaying homoeologous pairing.