A DETAILED RFLP MAP OF COTTON, GOSSYPIUM-HIRSUTUM X GOSSYPIUM BARBADENSE - CHROMOSOME ORGANIZATION AND EVOLUTION IN A DISOMIC POLYPLOID GENOME

We employ a detailed restriction fragment length polymorphism (RFLP) m ap to investigate chromosome organization and evolution in cotton, a d isomic polyploid. About 46.2% of nuclear DNA probes detect RFLPs disti nguishing Gossypium hirsutum and Gossypium barbadense; and 705 RFLP lo ci are assembled into 41 linkage groups and 4675 cM. The subgenomic or igin (A vs. D) of most, and chromosomal identity of 14 (of 26), linkag e groups is shown. The A and D subgenomes show similar recombinational length, suggesting that repetitive DNA in the physically larger A sub genome is recombinationally inert. RFLPs are somewhat more abundant in the D subgenome. Linkage among duplicated RFLPs reveals 11 pairs of h omoeologous chromosomal regions-two appear homosequential, most differ by inversions, and at least one differs by a translocation. Most homo eologies involve chromosomes from different subgenomes, putatively ref lecting the n = 13 to n = 26 polyploidization event of 1.1-1.9 million years ago. Several observations suggest that another, earlier, polypl oidization event spawned n = 13 cottons, at least 25 million years ago . The cotton genome contains about 400-kb DNA. per cM, hence map-based gene cloning is feasible. The cotton map affords new opportunities to study chromosome evolution, and to exploit Gossypium genetic resource s for improvement of the world's leading natural fiber.