Rhaedas

How much does this human mitochondrial DNA differ from related primates, or even further back? Given my limited understanding of how mtDNA is passed, other than through mutations, mtDNA should be common throughout related species as well, and indeed perhaps on down through all sexually reproducing organisms.

So in essence, the mitochondrial Eve doesn't stop at a single human female, but instead the "Eve" is a very distant proto-sex ancestor.

Or have I missed the boat on this one?

Jayjay

Yup. The lineage goes all the way down to the first cell with mitochondria (assuming there was only one of those). Mitochondrial Eve, however, is by definition the most recent person/organism in the line.

theyeti

You're basically right; closely related species will have more similar mtDNA than distantly related species. However, since mtDNA evolves much faster than nuclear DNA, the phylogenetic signal is quickly lost. Therefore, it's only good for building phylogenies with very closely related species or subspecies.

theyeti

Peez

Sorry, it is hard to discuss this without getting into a little jargon. I defined these terms very briefly in an earlier post (on that same page):An allele if one form of a gene. A locus (plural = loci) is the place where a gene is found. Thus, we all have a locus for insulin: this is the part of the chromosome that has the genetic code that is used as a blueprint for insulin. Humans have two copies of this code, one from each parent, and they are both considered to be the same locus. It is possible that the actual code found at this locus in not exactly the same in all people. Each variant is called an allele.

A simple example is the locus for a particular protein that forms chlorine channels in plasma membranes. There are at least two alleles known to be found at this locus, let's call them C and c. The most common allele, C, is the "normal" allele that codes for a protein that functions as a chlorine channel "normally." The other allele, c, is less common and codes for a protein that is slightly different: it does not function "normally" as a chlorine channel. Recall that humans get two copies of genetic code at each locus, that is two alleles at each locus. Most people get two C alleles (CC), but about 1 in 20 Europeans (IIRC) happen to get Cc. That's fine, even with one allele that produces a useless protein (c), the individual is fine because they have the other allele (C) and so can produce the chlorine channels that they need. However, if someone is so unfortunate as to get two c alleles (cc, about 1 in 1,600 Europeans IIRC) they cannot produce this chlorine channel and suffer from what is known as cystic fibrosis.

So, we each have 2 alleles at each locus: 2 at the chlorine channel locus, 2 at the insulin locus, 2 at the beta globin (part of haemoglobin) locus, etc. (there are a few exceptions in men). In the example I was giving, there were 6 individuals, so with 2 alleles at this locus for each individual: 2x6=12 alleles total in this tiny population. Of course they are not necessarily all different, we are just tracking the passing of these alleles from generation to generation.

Please let me know if this is not clear.

Peez

Peez

Looks good to me.

Peez

Peez

Others have answered this well, I will just add that this brings up a point that should not be missed: even though we have all inherited our mitochondria from one individual, that does not mean that we all have genetically identical mitochondria. Our mitochondria are the descendants of Eve's mitochondria, but evolution has occurred. The same applies to chimp mitochondria, etc.

Peez

Roller

Since I fancy those ERV insertions so much, I was thinking about something. If we all share ERV insertions, that would mean that mitochondrial "Eve" also had those insertions? Right? Which she, of course, also inherited.

Jayjay

Technically, that's not strictly necessary. The portion of DNA where the shared ERV is located might have been inherited from a more recent common ancestor than mitochondrial Eve. (Someone correct me if I'm mistaken.)

Of course if the ERV happens to be in mitochondrial DNA that's another thing entirely.