Duplicate Genetic Activities affecting Meiotic Chromosome Pairing at Low Temperatures in Triticum

Abstract

COMMON wheat, Triticum aestivum (2n = 42), is an allohexaploid with the genomic constitution AABBDD. One of its parents was a tetraploid, like T. dicoccum, with twenty-eight chromosomes and with an AABB genomic constitution. The A, B and D genomes—each of which contains seven chromosomes—were derived from closely related diploid species¹. Consequently, there are considerable levels of genetic duplication in T. dicoccum and of triplication in T. aestivum. This is formally recognized by the classification of the chromosome complements of both species into seven homoeologous groups². Homoeologous chromosomes are genetically corresponding members of different genomes the relationships of which are presumed to stem from their evolutionary origin from the same chromosome of the common progenitor of all three diploid ancestors. Twenty-one bivalents are usually formed at meiosis in T. aestivum and there is disomic inheritance. T. dicoccum has a similar diploid-like pattern of chromosome pairing with the regular formation of fourteen bivalents. Several distinct genetic activities are known to affect the regularity of meiotic pairing of T. aestivum^3–5 and it has been inferred that some of these activities are duplicated—being performed at more than one locus^5,6. This communication is concerned with the first unequivocal demonstration of such duplication and with the demonstration that different components of the system are responsible for the maintenance of meiotic regularity at low temperatures in different Triticum genotypes.