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Research shows that mitochondrial DNA can pass through fathers – what does this mean for genetics?

Some things that you learn in school are wrong, for example, that there are only five senses or three states of matter. Now, advanced research has been added to the list, proving that mitochondria (the energy sources in our cells) come from both our parents, and not – as biology students teach – only from our mothers.

The study, published in PNAS, convincingly showed that in three unrelated families, the mitochondria from the father's sperm were transferred to the children for several generations. The inverted scientific understanding of this fundamental “truth” opens the way for better treatment of mitochondrial disorders that affect many families with a devastating disease.

Mitochondria convert the sugars, fats, and proteins that we eat into molecules that our cells use to nourish. Therefore, when they go wrong, the result is often catastrophic, leading to life-long problems or even the death of the injured child in the womb.

For example, MELAS syndrome begins in early childhood and leads to seizures and dementia. Kearns-Sayre syndrome causes vision and hearing problems, potentially leaving blindness blind and deaf.

Most of the cell's DNA is contained in its nucleus, but the mitochondria sit separately inside the cell and have their own DNA. This is due to the fact that it is believed that mitochondria begin as separate organisms that entered early cells about 1.45 billion years ago and never left. They reproduce themselves and pass from one generation to another, "pressing the elevator" in the egg.

Mitochondria are the sources of cell energy.
Sebastian Kaulick / Shutterstock

During fertilization, the father’s sperm carries DNA into the egg, but few or none of the mitochondria of the sperm enter. If so, then there are mechanisms designed to destroy them. A new study showed that in a small number of families, the mitochondria from the father that fell into the egg were not destroyed, although we do not yet know enough to say why. There was also some evidence that this mitochondrial DNA from the father could then be copied, since the fertilized egg had turned into an embryo even larger than that of the mother.

The likelihood that previous studies may also have found examples of mitochondria transmitted to fathers, but that these results have been reduced and are considered to be the result of sample contamination. But with ever-growing technological advances, cheaper and deeper DNA analysis is possible. Therefore, it is likely that now more and more cases.

This work may affect scientists studying the movement of people around the planet. Human mitochondrial DNA tends to vary greatly over time, because even minor changes are often fatal, so they are not passed on to future generations. This means that human mitochondrial DNA can be very similar to human mitochondrial DNA with their distant ancestors and other people from their ethnic group.

Thus, by studying mitochondrial DNA in different populations, scientists were also able to follow how these groups move around the world and even identify a potential common ancestor for all people, known as "mitochondrial Eve." However, all this work was based on the "fact" that mitochondria pass only through the female line, which we now know is wrong.

Best treatment

The most significant effects of these findings are overwhelming, since a better understanding of how mitochondria are transmitted gives us much more chances to develop treatments for mitochondrial disorders. It may even be possible to encourage well-functioning mitochondria to multiply within the fertilized egg at the expense of broken ones.

Any treatment is likely to be controversial, because it will affect someone else's DNA in a way that will be inherited by subsequent generations. But the only other current therapy is also controversial and involves inserting a nucleus from a fertilized egg into a donor egg containing normal mitochondria. This is often referred to as producing “three parent children” and is not allowed in most countries, although the first such child was born in April 2016. Thus, the manipulation of parents' mitochondria can be considered as more preferable.

When it comes to our use of mitochondrial DNA to study the evolution and migration of humans, the rarity of the cases identified in the new study means that it will not have a significant impact on our understanding in this area. But if further research suggests that fathers mitochondrial DNA inheritance is more common, you may need to change our understanding of human migration.

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