| Polyploid formation has played a major role in the evolution of many plant and animal genomes, however, surprisingly little is known for us what happens to genomes in polyploidy. The genus Gossypium is a facile system for investigating the genomic organization and evolution. Gossypium includes about 51 species, grouped into 9 genome types. It has been proposed previously that extant A-and D-genome species are most closely related to the diploid progenitors of the tetraploid(A.D genome). Powerful new technologies have been begun to be brought to bear on the problem of the origin and evolution of tetraploid cotton, some investigators has gotten some same conclusions. Yet few data address the question of the actual diploid ancestor of tetraploid D-subgenome, the relationship between the diploid genome and tetraploid genome, and some diploids' homologous relationship, et al. Some research results are different from each other.Fluorescent in situ hybridization (FISH) is used to explore the origin and evolution of tetraploid cotton in this study. The contents include the diploid ancestors of tetraploid cotton, polyphyletic or monophyletic origin of tetraploid cotton, and rDNA concerted evolution. The main results are as follows:1.In this study, gDNA(genomic DNA) of A-genome diploid cotton G.herbaceum var.africanum and Garboreum and gDNA of the D-genome diploid cotton Graimondii, G.davidsonii, Gthurberi, Ggossypiodies are used as probe, respectively. The somatic cell and pollen mother cell of tetraploid cotton are used as target DNA, respectively. The results of A-genome diploid cotton gDNA as probe show that some A-genome dispersed repetitive sequences have "invaded" D-genome. The phenomenon that the A-genome of allopolyploid cotton is more similar to that of the A-genome diploids than the D-genome of the allopolyploid is to that of the D-genome diploids can be also observed in this study. Moreover, the results of D-genome diploid cotton gDNA as probe show that Gdavidsonii is the proposed D-genome progenitor of Ghirsutum, and Graimondii is the proposed D-genome progenitor of Gbarbadense. This result maybe implicate that tetraploid cotton are polyphyletic origin. Furthermore, Ggossypiodies is very special and different with other D-genome diploid cotton from FISH images demonstration.2.Signals in the hybrid of (AD) 1×A1-a show that more AA bivalent, sometimes AAA trivalent and AAAA tetravalent. This suggests that there are some differences between Gherbaceum var.africanum genome and Ghirsutum A-subgenome although they are almost same. Signals in the hybrid (AD) 2×D1 and (AD) 2×D5, the frequency of DD bivalent in two hybrids is almost same but Graimondii genome and Gbarbadense D-subgenome are more homologous than Gthurberi from the intensity of shown signals.3.In this study, 45S rDNA was used as probe hybridized with Ghirsutum, Gbarbadense, G.mustelinum as target DNA, respectively. In the results, rDNA of Ghirsutum, Gbarbadense havebeen homogenized to D genome repeat type, whereas rDNA of Gmustelinum have concerted to A genome repeat type. This phenomenon shows that interlocus concerted evolution can occur bidirectionally subsequent to hybridization and polyploidization. And all of the 45S major loci in tetraploid cotton were located on the terminal end of the short arms of chromosomes. These results implicate that 45 S rDNA can move from one region to another regions on one chromosome or from one chromosome to another chromosomes just like transponsons.
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