How does mitochondrial DNA change?

Question

It's been a few years since I took Cell biology. I know how most of it works and have a biology degree so if answer is technical that's ok. I can't remember how Mitochondrial DNA works. I know that mitochondria have their own DNA which is responsible for the synthesis and regulations of the proteins etc. necessary for cellular respiration. I also know that mitochondrial DNA is passed down maternally, which means it is used to identify maternal lines. However this would seem to indicate that mtDNA has variation between people from different maternal lines, however any variations would likely cause the Mitochondria to perform inefficiently or not at all of it caused a protein to code wrong. 

So I guess my question is how conserved is mitochondrial DNA? Does it have a lot of junk regions where these variations can occur harmlessly? (I wouldn't think so but may be wrong). How much variation is there between maternal lines and between different people not from the same family? And how much difference is there between the mtDNA of humans and other animals (assuming endosymbiosis, I would assume not much or it would lose functionality). 

Thank you

Beverly · Accepted Answer

Mitochondrial DNA (mtDNA or mDNA) is the DNA located in organelles called mitochondria, structures within eukaryotic cells that convert chemical energy from food into a form that cells can use, adenosine triphosphate (ATP). Nearly all of the DNA present in eukaryotic cells can be found in the cell nucleus, and in plants, the chloroplast as well.
In humans, mitochondrial DNA can be assessed as the smallest chromosome coding for only 37 genes and containing only about 16,600 base pairs. Human mitochondrial DNA was the first significant part of the human genome to be sequenced. In most species, including humans, mtDNA is inherited solely from the mother.
The DNA sequence of mtDNA has been determined from a large number of organisms and individuals (including some organisms that are extinct), and the comparison of those DNA sequences represents a mainstay of phylogenetics, in that it allows biologists to elucidate the evolutionary relationships among species. It also permits an examination of the relatedness of populations, and so has become important in anthropology and field biology

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How does mitochondrial DNA change?

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