Every one of us has two kinds of DNA. Standard DNA is housed in each cell nucleus and is inherited from both parents. Mitochondria, the little cellular power plants found in every cell, have their own independent set of DNA that is inherited from your mother only.
Recently a study, published in Genome Research, tested two rat strains that had identical nuclear DNA. They differed only in the mitochondrial DNA that encodes for proteins involved in energy production. The rat strain that had inherited variations in its mitochondrial DNA showed impaired glucose tolerance, less muscle glycogen synthesis, and other metabolic markers that typify type 2 diabetes.
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Sources: Genome Research, August 2007; EurekAlert