| Abstract: | It has been reported that there was a linkage of 5 S rRNA gene to 18 S-5.8 S-25 S rRNA gene in a few of species in Ochrophyta.In regard to the usual two positions of linked 5 S rDNA to the 3' end of 25 S rDNA,two pairs of primers were designed for amplification to verify this linkage of two genes in a kelp cultivar of Saccharina japonica,one of species in Ochrophyta.This result supplemented the previous report that 5 S rDNA was unlinked to 25 S rDNA in this kelp.In order to simultaneously visualize this unlinkage of two genes,dual-color fluorescence in situ hybridization(FISH) technique was applied to the cytogenetics of S.japonica.Dual-color FISH images showed that two and four hybridization signals were present in the kelp gametophyte and sporophyte,respectively,metaphase nuclei hybridized simultaneously with the labeled probes of 18 S rDNA and 5 S rDNA.Both haploid and diploid karyotypes in decreasing length of chromosomes showed that 18 S-5.8 S-25 S rDNA was localized at the interstitial region of Chromosome 23,whereas 5 S rDNA resided at the sub-telomeric region of Chromosome 27.These karyotypes suggested that the kelp nuclear genome had only one locus of each rRNA gene,and their loci on different chromosomes indicated the physical unlinkage of 5 S rDNA to 18 S-5.8 S-25 S rDNA in this kelp.Therefore,dual-color FISH seems to be a powerful technique for the discrimination and pairing of chromosomes featured in both small size and nearly identical shape in S.japonica. |
