The Genetic Control of Chromosome Pairing in Wheat

Abstract

Bread wheat is an allohexaploid with three pairs of homoeologous chromosomes. This means that each chromosome pair is present in three related but not truly homologous chromosomes. In order to maintain the integrity of the three chromosome sets, pairing must be very tightly controlled at meiosis to allow homologous but not homoeologous chromosomes to pair and recombine. Several genes (termed Ph genes) are known to be involved in controlling chromosome pairing in wheat, but the strongest effect has been associated with a gene on the long arm of chromosome 5B, Phl. The manipulation of this gene can be used to induce recombination between chromosomes that will not normally pair at meiosis. This has application in the introduction of new genetic information into wheat. Elucidation of the mechanism of action of the Ph genes has centred around genetic and cytogenetic studies with little attempt to investigate the molecular biology or biochemistry of these genes. Isolation of genes in meiosis in yeast and genes associated with the aerly stages of meiosis in lily have provided a potential entry point into the identification of the analogous genes in wheat.