Anil Suchdev

The importance of your mother’s mother. Everyone inherits mitochondrial DNA from their grandmothers only. Mitochondrial inheritance from the sperm is nil as it’s destroyed right after fertilization. Basically it means your mtDNA from your mother comes from her mother only. Your paternal grandmother does not contribute any mtDNA to you. mtDNA is passed only through the maternal line. Your paternal grandmother passed her mtDNA to your father, but fathers do not pass mtDNA to their children. Your mtDNA comes exclusively from your mother → maternal grandmother → maternal great-grandmother, and so on. Your paternal grandmother contributes a normal quarter of your nuclear DNA (and if you are female… her entire X chromosome via your father). She contributes nothing to your mitochondrial DNA. Of course nuclear DNA and environmental factors matter most in a person’s genetic makeup, but when a pathogenic mutation is present in the maternal line, it creates a heritable risk that can affect multiple generations on the mother’s side. Grandmothers are important. Maternal grandmothers are special.