Cibulskis R E
Department of Medical Protozoology, London School of Hygiene and Tropical Medicine.
Parasitology. 1988 Apr;96 ( Pt 2):303-22. doi: 10.1017/s0031182000058315.
Experimental work has established that a sexual process can occur in African trypanosomes (Jenni, Marti, Schweizer, Betschart, Le Page, Wells, Tait, Paindavoine, Pays & Steinert, 1986; Paindavoine, Zampetti-Bosseler, Pays, Schweizer, Guyaux, Jenni & Steinert, 1986; Tait, personal communication). However, the role of the process in natural populations of trypanosomes is poorly understood. This paper considers what information can be gained from analyses of isoenzyme polymorphism. A cladistic approach is used to help determine whether trypanosome diversity could have been produced by mutation alone. When applied to three East African populations of Trypanosoma brucei it provides evidence that some diversity has arisen through a sexual process; this explains the variation observed within a locality and can account for the evolution of differences between localities. However, the extent to which genetic exchange currently operates is less clear. Analysis of genotype frequencies indicates that agreements with Hardy-Weinberg expectations can be obtained even if genetic exchange exerted no influence over genotype frequencies. Moreover, analysis of joint locus frequencies reveals disequilibrium between loci and that trypanosome populations may be lacking several genotype combinations. Thus, genetic exchange may not occur sufficiently frequently, or in such a way as to break up associations between loci. The relevance of these observations to the evolution of strain differences within T. brucei is discussed.
实验工作已经证实，非洲锥虫中会发生有性生殖过程（詹尼、马尔蒂、施韦泽、贝沙尔、勒佩奇、韦尔斯、泰特、潘达瓦万、帕伊和施泰纳特，1986年；潘达瓦万、赞佩蒂 - 博塞勒、帕伊、施韦泽、居约、詹尼和施泰纳特，1986年；泰特，个人交流）。然而，这一过程在锥虫自然种群中的作用却知之甚少。本文探讨了从同工酶多态性分析中可以获得哪些信息。采用分支系统学方法来帮助确定锥虫的多样性是否仅由突变产生。当应用于三个东非布氏锥虫种群时，它提供了证据表明部分多样性是通过有性生殖过程产生的；这解释了在一个地区内观察到的变异，并能说明不同地区之间差异的演变。然而，目前基因交换的运作程度尚不清楚。对基因型频率的分析表明，即使基因交换对基因型频率没有影响，也能得到与哈迪 - 温伯格预期相符的结果。此外，对联合基因座频率的分析揭示了基因座之间的不平衡，并且锥虫种群可能缺乏几种基因型组合。因此，基因交换可能不会频繁发生，或者不会以打破基因座之间关联的方式发生。本文讨论了这些观察结果与布氏锥虫菌株差异进化的相关性。
