For years, modern science has been operating under the assumption that human mitochondrial DNA was always inherited matrilineally. Countless lab analyses and tests have confirmed this theory, but a recent discovery could uproot all of that.
The foundation of modern genetics
Our DNA is inherited from both of our parents, with parts of it mixing and mingling to create us as unique human beings, different from both of our predecessors. Mitochondrial DNA, however, has long been studied to hold only maternal DNA sequences.
Different from the rest of our body, the mitochondria within cells were believed only to contain genes passed down from mother to child. This one-sided contribution led to the use of mitochondrial DNA in maternity tests. That foundation has been shaken following a recent discovery.
Dr. Shiyu Luo from the Cincinnati Children’s Hospital Medical Center published a paper documenting several cases where paternal DNA was found within the mitochondria, as well as maternal DNA. The cases were rare, but the studies implied that the trait could be hereditary.
There also appeared to be a link between shared mitochondrial DNA and mitochondrial diseases. While the initial subject whose DNA led to this discovery was admitted to the hospital with suspected mitochondrial disease, tests showed no abnormalities other than the mixed lineage.
Although the number of documented cases of maternal and paternal DNA being present in the mitochondria is extremely small, the discovery brings into question the reliability of maternity testing. Additionally, people with mixed DNA could help scientists learn more about why most humans only have maternal mitochondrial DNA.
Human embryos contain both maternal and paternal mitochondrial DNA at the start. At some point during development in utero, the paternal DNA is singled out and destroyed, leaving behind only the maternal strands. The mechanisms behind this selection are currently unknown, but scientists hope that comparative testing might reveal answers.