In the Cercopithecini ancestor two chromosomes, homologous to human chromosomes 20 and 21, fused to form the Cercopithecini specific 20/21 association. In some individuals from the genus Cercopithecus , this association was shown to be polymorphic for the position of the centromere, suggesting centromere repositioning events. We set out to test this hypothesis by defining the evolutionary history of the 20/21 association in four Cercopithecini species from three different genera. The marker order of the various 20/21 associations was established using molecular cytogenetic techniques, including an array of more than 100 BACs. We discovered that five different forms of the 20/21 association were present in the four studied Cercopithecini species. Remarkably, in the two Cercopithecus species, we found individuals in which one homolog conserved the ancestral condition, but the other homolog was highly rearranged. The phylogenetic analysis showed that the heterozygosity in these two species originated about 8 million years ago and was maintained for this entire arc of time, surviving multiple speciation events. Our report is a remarkable extension of Dobzhansky’s pioneering observation in Drosophila concerning the maintenance of chromosomal heterozygosity due to selective advantage. Dobzhansky’s hypothesis recently received strong support in a series of detailed reports on the fruit fly genome. Our findings are first extension to primates, indeed to Old World monkeys phylogenetically close to humans of an analogous situation. Our results have important implications for hypotheses on how chromosome rearrangements, selection, and speciation are related.

中文翻译：

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尾猿猴染色体同源物保持八百万年的杂合性

在 Cercopithecini 祖先中，与人类 20 号和 21 号染色体同源的两条染色体融合形成 Cercopithecini 特定的 20/21 关联。在来自 Cercopithecus 属的一些个体中，这种关联被证明是着丝粒位置的多态性，表明着丝粒重新定位事件。我们开始通过定义来自三个不同属的四个 Cercopithecini 物种中 20/21 关联的进化历史来测试这一假设。各种 20/21 关联的标记顺序是使用分子细胞遗传学技术建立的，包括 100 多个 BAC 的阵列。我们发现在四个研究的 Cercopithecini 物种中存在五种不同形式的 20/21 关联。值得注意的是，在两个 Cercopithecus 物种中，我们发现其中一个同源物保留了祖先状况，但另一个同源物高度重排的个体。系统发育分析表明，这两个物种的杂合性起源于大约 800 万年前，并在整个时间弧内保持，在多次物种形成事件中幸存下来。我们的报告是 Dobzhansky 在果蝇中关于由于选择性优势而维持染色体杂合性的开创性观察的显着扩展。Dobzhansky 的假设最近在一系列关于果蝇基因组的详细报告中得到了强有力的支持。我们的发现首先扩展到灵长类动物，实际上扩展到在系统发育上与人类相似的旧世界猴子。我们的结果对关于染色体重排、选择、