Distribution of genes and recombination on wheat homoeologous group 6 chromosomes: a synthesis of available information

Abstract

Presence of genes in gene-rich regions on wheat chromosomes has been widely reported. However, there is a lack of information on the precise characterization of these regions with respect to the distribution of genes and recombination. We attempted to critically analyze the available data to characterize gene-rich regions and to study the distribution of genes and recombination on wheat homoeologous group 6 chromosomes which are a reservoir of several useful genes controlling traits of economic importance. Consensus physical and genetic linkage maps were constructed for homoeologous group 6 using physical and genetic mapping data. Five major gene-rich regions were identified on homoeologous group 6 chromosomes, with two on the short and three on long arm. More than 90% of marker or gene loci were present in these five gene-rich regions, which comprise about 30% of the total physical chromosomal length. The gene-rich regions were mainly present in the distal 60% regions of the chromosomes. About 61% of the total loci map in the most distal regions which span only about 4% of the physical length of the chromosome. A range of sub-microscopic regions within each gene-rich region were also identified. Comparisons of the consensus physical and genetic linkage maps revealed that recombination occurred mainly in the gene-rich regions. Seventy percent of the total recombination occurred in the two most distally located regions that span only 4% of the physical length of the chromosomes. The relationship of recombination to the gene-rich region is not linear with distance from the centromere, especially on the long arm. The kb/cM estimates for group 6 chromosomes ranged from 146 kb in the gene-rich to about 10 Mb in the gene-poor region. The information obtained here is vital in understanding wheat genome structure and organization, which may lead in developing better strategies for positional cloning in wheat and related cereals.