Molecular Cytogenetical approach on Chromosome evolution in Schistosomes.

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1. Meiotic chiasma frequency was estimated in male Schistosoma mansoni (Sm), Schistosoma japonicum (Sj), and Paragonimus ohirai (Po) using two methods. The first technique (T-I) assumed the presence of achismatic terminal associations and the second (T-II) assumed the occurrence of terminalized chiasmata. The T-I method yielded a mean cell chiasma frequency of 15.27, 15.25, and 3.0 for Po, Sm, and Sj, respectively, and T-II yielded 20.72, 18.30, and II.70. The T-I may provide more accurate meiotic chiasma frequency than the T-II.Relationship between differentiation of chiasma frequency and speciation in schistosomes were discussed.2. Fluorescence in situ hybridization (FISH) for YAC clones of Schistosoma mansoni was developed. Over one hundred YAC clones were localized by FISH and found to be distributed widely among all the chromosomes. An assembly of 16 YACs covered approximately the entire region of chromosome 3. These results indicate that the extensive contig assembly of each chromosome should be feasible.3. Chromosomal localization of rDNA in sample of five taxa of the Myrmecia pilosula species complex was carried out by FISH.From the results, we suggest that the rDNA in the ancestral stock of the M.pilosula complex was localized originally in a pericentromeric C-band, and multiplied by chance with time during saltatory increases in C-banding following episodes of centric fission.