Straight Dope Message Board

[Jim B.]

Does Mitochondrial DNA ever mutate? You certainly never hear of that happening.

In case you don't know, the Mitochondria are those little dark oval-shaped things in your cell, from HS biology class. I think they are responsible for metabolizing energy in the cell. Or something like that. And I know that they have DNA because I heard in the news how they are sometimes used to establish maternal ancestry. (They are passed from ovum to ovum. Until they reach a male heir. Then they are received, but not passed on.)

Thank you all in advance for your kindly replies.

1

[Ludovic]

They couldn't be used to establish maternal ancestry if they didn't mutate. If they didn't mutate, everyone would have exactly the same copy and it would then be useless. Instead, everyone has slightly different copies that can be used for genealogy and if they mutate in the wrong way can be one of the causes of mitochondrial disease. 2

[Melbourne]

Originally Posted by Jim B.

Does Mitochondrial DNA ever mutate? You certainly never hear of that happening.

In case you don't know, the Mitochondria are those little dark oval-shaped things in your cell, from HS biology class. I think they are responsible for metabolizing energy in the cell. Or something like that. And I know that they have DNA because I heard in the news how they are sometimes used to establish maternal ancestry. (They are passed from ovum to ovum. Until they reach a male heir. Then they are received, but not passed on.)

Thank you all in advance for your kindly replies.

Mitochondrial DNA is inherited only from the mother. So mitochondria is not created with the essentially random mixing of two independent inputs. That random mix is why we can breed for traits in horses or dogs... or humans. But starting with two random humans, you get a third random human. Darwin's suggestion that, by selecting for certain traits, you could get a new species (The Origin of Species), depends on the development of new and different information, not simply inherited from your parents*.

The development of new information is now called mutation. When you get a helpful mutation, you can then use breeding to select for the new mutation. When you know what mutation you want, you can now use 'genetic engineering' to create the mutation, followed by selective breeding to get the population you want.

Different species, and different structures, get different rates of mutation, and different rates of helpful mutation. I don't know where mitochondrial DNA falls on that scale. But for DNA analysis, the import points are that (1) There is mutation, and (2) the mutation isn't obscured by random breeding.

*Or, there could be sufficient information in every DNA line for all DNA-based life, for every species that ever existed, and every species that will ever exist. That doesn't seem to be the case. 3

[Chronos]

Sexual reproduction doesn't increase the rate of mutation, but it increases the rate at which mutations can spread through the population. If you start with a population of a bunch of big gray dogs and want to breed a small brown dog, you can wait for a mutation for a brown dog to arise, and at the same time wait for a mutation for a small dog to arise, and then breed the small dog and the brown dog together, and you might get some that are both small and brown. Without sexual reproduction, you'd have to wait for mutations for one trait, and once you had it build up that population, and then wait for mutations in the other trait.

Mitochondria, of course, don't have sex in the same sense that we do. Many single-celled creatures have developed other ways of exchanging genes that serve the same purpose, but I don't think mitochondria have any of those, either. So changes spread slowly. 4

[Darren Garrison]

All genetic material mutates, period, end of sentence, tiny little dot. Mitochondrial DNA on the order of a hundred times faster than nuclear DNA. 5

[Iggy]

Yes, mitochondria DNA mutates. Understanding the mutation rate allows geneticists to perform analysis to determine how much time has elapsed since the last common ancestor of two species being compared.

It has been long though that mitochondrial DNA in humans is only maternally inherited. But in the last couple decades has it been confirmed that there can be paternally derived mitochondrial DNA in humans as well. A better understanding of this process and how frequently it occurs could refine our understanding of evolutionary DNA analysis. 6