“We have 46 chromosomes, half from our mother and half from our father,” he explained, hands flying about like those of an orchestra conductor. “That means that for each gene we receive two copies, one from each parent, and these two copies interact. This is not true for two small pieces of our DNA: the Y chromosome, inherited from male to male (the females do not have it), and the mitochondrial DNA, inherited from female to female (the males do have it, but they cannot pass it to their offspring). This peculiarity makes it much easier to trace back the history of a population through the
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