Word: mitochondria
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Dates: during 1980-1989
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Most of the DNA in human cells is in the cell nucleus, in the form of chromosomes. Since chromosomes come from both parents, this nuclear DNA is reshuffled with each generation, confusing the line of inheritance. But there is also DNA outside the nucleus, in mitochondria, substructures within each cell that are responsible for producing energy the cell needs. Since the sperm's mitochondria do not survive fertilization intact, mtDNA is inherited solely through the mother. The only way it can change over the generations is through mutation. And that mutation, evidence suggests, proceeds at a steady, known rate...