Molecular Cytogenetical approach on Chromosome evolution in Schistosomes.

1.用两种方法估计了曼氏血吸虫雄性(Sm)、日本血吸虫(Sj)和日本并殖吸虫(Po)的减数分裂交叉频率。第一种技术(T-I)假设存在无性终末联系，第二种(T-II)假设终止性交叉的发生。T-I法得到Po、Sm和Sj的平均细胞交叉频率分别为15.27、15.25和3.0，T-II的平均细胞交叉频率为20.72、18.30和2.70。T-I法可能比T-II法提供更准确的减数分裂交叉频率，并讨论了血吸虫交叉频率分化与物种形成的关系。建立了曼氏血吸虫YAC克隆的荧光原位杂交技术。FISH定位了100多个YAC克隆，发现它们广泛分布于所有染色体上。16个YAC的组装几乎覆盖了3号染色体的整个区域。这些结果表明，每个染色体的广泛重叠群组装应该是可行的。用FISH方法对五个物种复合体标本中的rDNA进行了染色体定位。结果表明，该复合体祖先群体中的rDNA最初定位于着丝粒周围的C-带，并在C-带的跳跃性增加过程中随时间而倍增。

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.