First some credit to God:
At the and of Y11 at high school my biology test result were showing a final grade between B and C. I asked my teacher before the end of the school year whether I can go for the better mark with some extra testing, and she said yes. So on the very last lesson of the whole year she stood me up and told the whole class to ask anything from me from that year’s topics. I was answering questions for almost 45 minutes, then the bell rang. And to my biggest surprise I got an A at the end of the year. As I had to study through it all again and answer heaps of questions, those topics got burnt into my mind. These were about how the body breaks down sugar, fat, and other things in multiple steps by using various enzymes, and my very last question was about mitochondrium. About 13 years later I understood why I had to go through all this: when doctors started talking about enzyme deficiency and mitochondrial genetic testing of my son I did not freak out for having no clue what they were talking about. I did not remember it in very details but I had a general understanding what they were saying, what their assumptions are (and they turned out to be right). So I did some research. I am not a scientist, just a mother who digged up stuff about enzymes and mitochondrium.
As I understood, the mitochondrium, which is the “powerhouse” part of a cell, has its own DNA, which is different to the ones in the cells we usually learn and hear about (the spiral one). This one has a ring form, and is called mDNA or mtDNA (to distinguish from the spiral DNA). mDNA goes (at least supposed to) from mother to child without any change. The child’s mDNA is the same as the mother’s - unless there is some error when the copies are made, i.e. “mitochondria are normally inherited exclusively from the mother”. Mutations though still happen, but it’s rare (a microbiologist told me that if my son had a mDNA related enzyme deficiency the chance to have another with the same issue is 1:40000 as I am healthy). There are though families (I read a lot of articles those days) carrying the same mDNA mutation - carried over on the mother’s lineage - and all of them having the symptoms of that particular condition/illness.
Because it comes solely from the mother’s side it can be used to trace down ancestors - taking into consideration the possibility of mutation.
I know it’s not a scientific writing but I hope I could give you a bit more insight into this fascinating territory.