Zhang Q, Tibayrenc M, Ayala F J
Department of Genetics, University of California, Davis 95616.
J Protozool. 1988 Feb;35(1):81-5. doi: 10.1111/j.1550-7408.1988.tb04081.x.
We have studied linkage disequilibrium in natural populations of Trypanosoma cruzi, the agent of Chagas' disease, by analyzing (i) a set of 524 stocks from the whole geographical range of the parasite, characterized at four gene loci coding for enzymes; (ii) a subsample of 121 stocks characterized at 12 enzyme loci; and (iii) a subset of 386 stocks from six locations in Bolivia, characterized by four enzyme loci. Our results show that the linkage disequilibrium reaches the maximum possible value, given the observed allelic frequencies, for almost all the locus pairs. This result is most consistent with the hypothesis that genetic recombination is absent or very rare in T. cruzi natural populations. Partition of the linkage disequilibrium variance for the six Bolivian populations shows that both inter- and intrapopulation components are substantial and that the relationships among the components are D2IS less than D2ST, and D'2IS less than D'2ST. These inequalities are interpreted as the result of an interplay between genetic drift, rare or absent mating, and clonal selection in generating linkage disequilibrium in T. cruzi populations.
我们通过分析以下样本，研究了恰加斯病病原体克氏锥虫自然种群中的连锁不平衡现象：（i）从该寄生虫整个地理分布范围内选取的一组524个样本，对编码酶的四个基因座进行了特征分析；（ii）对121个样本的子样本进行了12个酶基因座的特征分析；（iii）从玻利维亚六个地点选取的386个样本子集，对四个酶基因座进行了特征分析。我们的结果表明，对于几乎所有的基因座对，连锁不平衡达到了给定观察到的等位基因频率时的最大可能值。这一结果与克氏锥虫自然种群中不存在或极少发生基因重组的假设最为一致。对六个玻利维亚种群的连锁不平衡方差进行划分，结果表明种群间和种群内的成分都很显著，且成分之间的关系为D2IS小于D2ST，D'2IS小于D'2ST。这些不等式被解释为基因漂变、极少或不存在交配以及克隆选择在克氏锥虫种群中产生连锁不平衡时相互作用的结果。
