有些科学家提出，我们从母体遗传来的线粒体DNA很少发生变异，说明瓶颈发生在不久以前祖先走出非洲的时候。
Some researchers proposed that the lack of variation in our maternally inherited mitochondrial DNA suggested these bottlenecks took place as our ancestors spread out of Africa relatively recently.
由于母体的可遗传变异使得这些特殊的细胞不可能被用于繁殖，但是能够帮助科学家总结出繁殖过程。
Although this particular batch of cells is unlikely to be used for assisted reproduction because of the donor's heritable mutation, it will help scientists work the process out.
母体， 随机样本。 样本统计， 样本平均数和变异数的动差。
Populations, random samples. Sample statistics, moments of the sample mean and variance.
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