Unexpectedly, fathers can pass on mitochondrial DNA.
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Unexpectedly, fathers can pass on mitochondrial DNA.

Today we are going to talk about a new research
that is challenging a widely accepted view that mitochondrial genome is only maternally transmitted in humans. First what are mitochondria and why they matter? Mitochondria are energy producing organelles. When we think about energy production in animal
cells we actually think about mitochondria which are the part of the cell that uses oxygen
and different organic molecules to produce a lot of energy that allows us to move and
think and basically live. They are important because the other process
we use to produce energy – namely anaerobic energy production – generates way less energy
than mitochondria do so we really need them. Also one interesting feature about these cellular
organelles is that they actually have their own genome. And it is a special one. Evolutionary mitochondria appeared due a collaboration
of some aerobic bacteria and anaerobic eukaryotic cells. It was a mutually beneficial collaboration
as eukaryotic cells provided shelter and food and bacterial cells used oxygen to provide
a lot of energy for the eukaryotic cell. Due to this symbiosis eukaryotic cells today
have mitochondria and are aerobic. But mitochondria essentially remained little
bacteria inside eukaryotic cells and because of it they still have their genome and their
genome is structured as a bacterial genome and we have thousands of copies of mitochondrial
genome per cell as opposed to just two copies of nuclear genome. To make things more interesting all of the
previous research have indicated that in mammals mitochondrial genome is only maternally transmitted
with some minor exceptions of course. And humans being typical mammals do the same
– human mitochondria are coming only from the mother and never from father’s sperm. Why evolution needs that is not clear because
I think you would agree that it is highly discriminatory but still we do not know why. Of course there are mechanisms described in
different animals and other organisms which allow for the specific paternal mitochondrial
DNA destruction after fertilization, but that does not clears the reason why we go to such
lengths to do that. And now a new research has shown that in some
rare cases mitochondrial DNA can be transmitted paternally as well. Researchers initially studied a 4 year old
patient which was suspected of a mitochondrial disease which is due to mutations in mitochondrial
DNA. Sequencing mitochondrial genome of this patient
researchers haven’t find any pathogenic mutations but they have found a very unusual pattern
of mitochondrial DNA variation which could be explained by paternal transmission only. So they’ve sequenced mitochondrial DNA in
other two labs to be sure that this is not some kind of a problem with their equipment
or their protocols. And the results still suggest that this patient
have received mitochondrial DNA from his father and not only his mother. When researchers studied his entire family
they found other members which also inherited mitochondrial DNA from their fathers. Overall researchers have found 17 different
people from 3 unrelated families which have mitochondrial DNA inherited from their fathers. We do not understand how that happened but
most probably there are some mutations in nuclear DNA which is responsible for the paternal
mitochondrial DNA destruction so these people could be very important for our understanding
how the genes involved in this process work and what genes are these. This work could be very important for our
understanding of mitochondrial DNA transmission and maybe we even could help families with
diseases caused by mutations in mitochondrial DNA to have healthy children without using
very complicated techniques as in case of three parent babies which made headlines in
2016. The most interesting part of this work is
that when researchers have received their results, instead of dismissing them as some
error, they tried to elucidate the reasons and came with an unexpected discovery. Well done. So what do you think? Do you think you have only maternal mitochondrial
DNA or you are also some kind of exception? Let me know in the comment section down below
and I will see the next time.

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