These are not your mother's genes: mitochondrial DNA can come from dad

We learned in our biology classes that mitochondrial DNA only comes from the mother. But now, this theory needs to be rewritten.

A new study suggests that in three unrelated families, the mitochondria of the father's sperm had been passed on to children for several generations. The study conducted by geneticist Taosheng Huang of the Cincinnati Children's Hospital Medical Center shows that human mitochondrial DNA can be inherited paternally.

Huang observed this by caring for a sick four-year-old boy. The child, who showed signs of fatigue, muscle aches and other symptoms, was evaluated by doctors and tested to determine if he was suffering from a disorder. mitochondrial.

When Huang did the tests – and did them again to be sure – he could not understand the results. He thought there had been a mistake.

Huang's patient, a four-year-old boy, wore two different sets of mitochondrial DNA: one from his mother, as expected, and the other from his father. It was only the beginning. Using modern DNA sequencing technology, Huang and his associates have definitively verified the inherited mitochondrial DNA in 17 people in three unrelated families.

Xinnan Wang, a biologist at Stanford University, said, "It's a truly revolutionary discovery. This could open up a whole new field … and change the way we look for the cause of [certain] diseases. "

Haung noted, "We are each a genetic mix of mom and dad. In the nucleus, which contains our chromosomes, this is true. But the nucleus is not the only part of the cell containing DNA. The cells contain power centers called mitochondria that also carry their own sets of DNA. In almost all known animals, mitochondrial DNA is inherited exclusively from the mother. This unbalanced acquisition is so entrenched that researchers often analyze mitochondrial DNA to trace maternal lineages in the past. "

Most of the DNA in a cell is contained in its nucleus, but the mitochondria are separately inside the cell and have their own DNA. Indeed, mitochondria are thought to have started as distinct organisms, which entered the first cells about 1.45 billion years ago and never left. They breed and pass from one generation to the next by "hitching a lift" in the egg.

During fertilization, the father's sperm transfers the DNA into an egg, but little or no sperm mitochondria enter the egg. It is very likely that there are mechanisms to erase them. The new research found that in a few families, the mitochondria of the father who had found his way in the egg was not devastated, but we have not yet become sufficiently aware of why.

There was also evidence that this dad's mitochondrial DNA may have been replicated while the fertilized egg had become a far more fetus than the mother's.

This discovery should help scientists to study the movement of humans around the planet.

Human mitochondrial DNA tends to change very little over time because even very small changes are often fatal and are not transmitted to future generations. This means that a person's mitochondrial DNA will probably be very similar to that of his distant ancestors and other people from his ethnic group.

By studying mitochondrial DNA in different populations, scientists have also been able to track the movements of these groups around the world and even identify a potential common ancestor for all humans, called "mitochondrial watch" .

The most significant implications of these results are enormous, as a better understanding of how mitochondria are transmitted gives us a much better chance of developing treatments for mitochondrial disorders.

Their work appears today in the journal PNAS.