Physical Mapping 25S RDNA On Several Primary Trisomics Of Chinese Cabbage (Brassica Campestris L.ssp.pekinensis(Rupr.) Olsson)

Primary trisomic was basic material in the research of gene location, construction of physical mapping and chromosome engineering , but study on trisomics of Chinese cabbage was very limited in the world. By mitotic chromosome karyotype analysis, three primary trisomic lines and a double trisomic line were further identified definitely. On the basis of it the number of major rDNA loci was investigated in the Chinese cabbage by in situ hybridization of an 25 S rDNA probe to metaphase chromosomes.Repetitive DNA sequences was the most available tool for the reseach of species filiation and evolution. In higher plant genomes, the repetitive sequences is widely in existence. 25S rDNA is present as tandem repeat units, the distribution of 25S rDNA in the trisomics of Chinese cabbage is helpful to understand the microevolution within the species.The gene sites on different trisomics of Chinese cabbage can be visualized by fluorescence in situ hybridization. The result was as follows:1 Aneuploid line 9408-2 was further definitely designated as trisomic 2, line 9408-3 as trisomic 8, line 9408-4 as trisomic 10, line 9408-5 as double trisomics-3,6.2 Trisomic 2 showed five 25S rDNA loci. In chromosome 2 two hybridization block was localized about the centromere of two homologous chromosomes respectively, another chromosome 2 had no hybridizaton siganal ; one somewhat smaller loci is located in the middle of long arms of one largest submetacentric chromosome 3, the other homologous chromosome had no hybridization siganal. The largest hybridization sites correspond to the NOR region of the largest satillite-carrying chromosomes3 In Trisomic 8, seven 25S rDNA hybridization sites were distinguishable on chromosomes. The single 25S rDNA loci located at the end of a short arm on the chromosome 1, the other homologous chromosome had no signal. The one of homologous chromosomes have two hybridization signal near the centromeric region of chromosome 2, the other homologous one had no signal. Two weak fluorescence signals were localized near centromeric regions of the two homologous chromosomes 3 respectively. Another middle size hybridization site was detected near the centromeric region of chromosome 6, no hybridization signal was detected on the other homologous chromosome . The largest hybridization site corresponds to the NOR region of the satillite -carrying chromosome.4 In trisomic 10, six 25 S rDNA hybridization sites were detected. A mediumsize signal was localized at the proximal region of the long arm on one of thehomologous chromosomes 2, two hybridization sites in the vicinity of centromericregion showed on the other homologous one were detected. One weak hybridizationsignal was detected on the long arms of chromosome 3, the other homologous one hadno hybridization signal detected. Two strongest hybridization signals were detectedcorresponding to the NOR region of the satellite-carrying chromosomes.5 In the double trisomic 3,6, six hybridization sites were detected. Three weaksignal existed near the centromeric region of three homologous chromosome 3respectively. One intense signal distribute on the satillite. the other on the long arm ofthe satillite-carrying chromosome, another one was located on the satillite of thehomologous satellite-carrying chromosomes.