Genetic history of indigenous peoples of the Americas primarily focus on Human Y-chromosome DNA haplogroups and Human mitochondrial DNA haplogroups. "Y-DNA" is passed solely along the patrilineal line, from father to son, while "mtDNA" is passed down the matrilineal line, from mother to offspring of both sexes. Neither recombines, and thus Y-DNA and mtDNA change only by chance mutation at each generation with no intermixture between parents' genetic material. Autosomal "atDNA" markers are also used, but differ from mtDNA or Y-DNA in that they overlap significantly. AtDNA is generally used to measure the average continent-of-ancestry genetic admixture in the entire human genome and related isolated populations.
What is the only way that Y-DNA and mtDNA change? (If the question is unanswerable, say "unanswerable")
chance mutation