Grossman A I, Short R B, Cain G D
Chromosoma. 1981;84(3):413-30. doi: 10.1007/BF00286030.
The morphology of C-banded metaphase chromosomes has been studied in two hermaphroditic and ten gonochoristic digenetic trematodes (schistosomes). Comparison of numbers and morphology of chromosomes indicates that the karyotype of primitive trematodes probably was composed of 10 (or 11) pairs of telocentric or subtelocentric chromosomes, and reduction of chromosome numbers in advanced species resulted from centromeric fusion rather than elimination of chromosomes. Observation of heteromorphic chromosomes in a hermaphroditic trematode (Spirorchis) suggested a differentiation of "pre-sex" chromosomes in species ancestral to dioecious trematodes which possess distinctly differentiated sex chromosomes. Our results indicate that differentiation of Z and W chromosomes in the gonochoristic trematodes resulted from: (a) partial constitutive heterochromatinization of the W chromosome (Schistosoma mansoni and S. haematobium complexes, African schistosomes), (b) deletion of part of the W (S. japonicum and S. mekongi, Asian schistosomes), and (c) translocation of part of one sex chromosome onto another (Schistosomatium douthitti and Heterobilharzia americana, American schistosomes) with subsequent heterochromatinization of the W in H. americana.
对两种雌雄同体和十种雌雄异体的复殖吸虫（血吸虫）的C带中期染色体形态进行了研究。染色体数量和形态的比较表明，原始吸虫的核型可能由10（或11）对端着丝粒或亚端着丝粒染色体组成，高等物种中染色体数量的减少是由于着丝粒融合而非染色体消除。在一种雌雄同体吸虫（旋睾吸虫）中观察到异形染色体，这表明在具有明显分化性染色体的雌雄异体吸虫的祖先物种中存在“前性”染色体的分化。我们的结果表明，雌雄异体吸虫中Z和W染色体的分化是由于：（a）W染色体的部分组成型异染色质化（曼氏血吸虫和埃及血吸虫复合体，非洲血吸虫），（b）W的部分缺失（日本血吸虫和湄公血吸虫，亚洲血吸虫），以及（c）一条性染色体的部分易位到另一条染色体上（杜氏血吸虫和美洲异毕吸虫，美洲血吸虫），随后美洲异毕吸虫中的W发生异染色质化。
