（六）放射性同位素，是指化学元素中具有相同原子序数，但质量不同且能发生放射性衰变的核素。
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Not every modern human has the same set of Neanderthal DNA, however; different people will, by chance, have inherited different fragments. But there are also some areas, termed "Neanderthal deserts," where none of the Neanderthal DNA seems to have persisted. Notably, the largest Neanderthal desert is the entire X chromosome, raising questions about whether this reflects the evolutionary fitness of genes there or mating preferences.
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