Comparative RFLP maps of the homoeologous group-2 chromosomes of wheat, rye and barley.

Genetic maps of the homoeologous group-2 chromosomes were constructed, comprising 114 loci in wheat and 34 loci in rye. These include the genes coding for sucrose synthase, sedoheptulose-1,7-bisphosphatase, a bZIP protein (EmBP-1), a peroxidase and an abscisic acid-induced protein (#7). Overall, gene orders are highly conserved in the genomes of wheat, barley and rye, except for the distal ends of chromosome arms 2BS and 2RS, which are involved in interchromosomal, probably evolutionary, translocations. Clustering of loci in the centromeric regions of the maps, resulting from the concentration of recombination events in the distal chromosomal regions, is observed in wheat and rye, but not in barley. Furthermore, loci for which homoeoloci can be detected in rye and barley tend to lie in the centromeric regions of the maps, while non-homoeologous and wheat-specific loci tend to be more evenly distributed over the genetic maps. Mapping of the group-2 chromosomes in the intervarietal 'Timgalen' x 'RL4137' cross revealed that the T. timopheevi chromosome segment introgressed into chromosome 2B in 'Timgalen' is preferentially transmitted. Recombination is also greatly reduced in that segment.