Chromosome structural changes in diploid and tetraploid A genomes ofGossypium

Abstract

The genus Gossypium, which comprises a divergent group of diploid species and several recently formed allotetraploids, offers an excellent opportunity to study polyploid genome evolution. In this study, chromosome structural variation among the A, At, and D genomes of Gossypium was evaluated by comparative genetic linkage mapping. We constructed a fully resolved RFLP linkage map for the diploid A genome consisting of 275 loci using an F2interspecific Gossypium arboreum × Gossypium herbaceum family. The 13 chromosomes of the A genome are represented by 12 large linkage groups in our map, reflecting an expected interchromosomal translocation between G. arboreum and G. herbaceum. The A-genome chromosomes are largely collinear with the D genomes, save for a few small inversions. Although the 2 diploid mapping parents represent the closest living relatives of the allotetraploid At-genome progenitor, 2 translocations and 7 inversions were observed between the A and Atgenomes. The recombination rates are similar between the 2 diploid genomes; however, the Atgenome shows a 93% increase in recombination relative to its diploid progenitors. Elevated recombination in the Dtgenome was reported previously. These data on the Atgenome thus indicate that elevated recombination was a general property of allotetraploidy in cotton.Key words: comparative mapping, polyploidy, genome evolution, inversions, translocations, RFLP.