wt are mitochondrial eve and mDNA?

http://www.talkorigins.org/faqs/homs/mitoeve.html
Here are some points to note:

The name Eve, in retrospect, is perhaps the worst possible name to give to the entity in question. I believe that this is probably the cause of so much confusion in understanding what the significance of this entity is. People think that this title has some deep theological or religious consequences. Nothing of that sort. Someone you come across who claims that the bible (or the book of Genesis) has been validated by the discovery of the Mitochondrial Eve, is talking crap---you should feel free, and even obligated, to tell them so.
The Mitochondrial Eve of 200,000 years ago (ME for short henceforth) is NOT our common ancestor, or even common genetic ancestor. She is the most-recent common ancestor of all humans alive on Earth today with respect to matrilineal descent. That may seem like a mouthful, but without even a single one of those qualifying phrases, any description or discussion of the ME reduces to a lot of nonsense.
While each of us necessarily has two parents, we get our mitochondria and mitochondrial DNA from the ovum (and hence from our mothers). Our mothers got their mitochondrial DNA from their mothers and so on. Thus, while our nuclear DNA is a mish-mash of the DNA of our four grandparents, our mitochondrial DNA is an almost exact copy of the DNA of our maternal grandmother (the match may not be exact due to mutations. In fact, the mutations in the mitochondrial DNA provide the molecular clock that allows us to determine how much time has elapsed since the ME lived).
The ME represents that woman whose mitochondrial DNA (with mutations) exists in all the humans now living on Earth. That does not mean that she is our lone woman ancestor. We have ancestors who are not via matrilineal descent. For example, our father's mother (who did pass on her mitochondrial DNA to her daughters) is an example of an ancestor who is not matrilineal to us. However, she did exist at one time and was probably of the same age as our mother's mother, who is a matrilineal ancestor of ours and from whom we got our mitochondrial DNA.

The term Mitochondrial Eve itself is a title given retroactively to a woman. Often (and as is certainly the case with the ME that we are discussing) the conferring of the title occurs many hundreds of thousands of years after the death of the woman in question.

ME lived with many other humans (men and women); she was certainly not alone. When she was alive, she was most certainly NOT the Mitochondrial Eve. The title at that time was held by a distant ancestor of hers (and of the many humans who were her contemporaries).

The existence of the Mitochondrial Eve is NOT a theory; it is a mathematical fact (unless something like a multiple-origins theory of human evolution i.e. the human species arose independently in different geographically separated populations, and that the present-day ease of interbreeding is the result of a remarkable convergent evolution, is true. Few people subscribe to the multiple-origins theory, and the Mitochondrial Eve observation is a refutation of multiple-origins).

The proof for the existence of a Mitochondrial Eve is as follows (based on an argument by Daniel Dennett in the above mentioned book).
Consider all the humans alive today on Earth. Put them into a set S.
Next, consider the set of all those women who were the mothers of the people in the set S. Call this set S'. A few observations about this new set S'. It consists of only women (while set S consists of both men and women)---this is because we chose to follow only the mother-of relationship in going from set S to set S'. Also note that not every member of set S' needs to be in set S---set S consists of all people living today, while some of the mothers of living people could have died, they would be in set S' but not in set S. Third, the size of set S' is never larger than the size of set S. Why? This is because of the simple fact that each of us has only one mother. It is however overwhelmingly more likely that the size of set S' is much smaller than that of set S---this is because each woman usually has more than one child.
Repeat the process of following the mother-of relationship with set S' to generate a new set S''. This set will consist of only women, and will be no larger (and very likely smaller) than set S'.
Continue this process. There will come a point when the set will consist of smaller and smaller number of women, until we finally come to a single woman who is related to all members in our original set via the transitive-closure of the mother-of relation. There is nothing special about her. Had we chosen to follow the father-of relation, we would have hit the Y-chromosome Adam (more on him later). Had we chosen to follow combinations of mother-of and father-of relations, we would have hit some other of our common ancestors. The only reason why the mother-of relationship seems special is because we can track it using the evidence of mitochondrial DNA.
Thus there must exist a single woman whose is the matrilineal most-recent common ancestor of every in set S.
A few others points to keep in mind. One might say that if each woman has only a single daughter (and however many sons), the size of the sets will be the same as we extrapolate backwards. But also note that this backwards mathematical extrapolation is an extrapolation into the past. This process cannot be continued indefinitely because the age of the Earth, life on Earth, and the human species is finite (this argument comes from Dawkins).
Also important to keep in mind is that while the final set S'* has only one member (the Mitochondrial Eve), she was by no means the only living woman on Earth during her lifetime. Many other women lived with her, but they either did not leave descendents or did not leave descendents via the matrilineal line, who are still alive today.

Let us now see how the title of Mitochondrial Eve can change hands.
Consider an extremely prolific woman living today. She has many daughters and takes a vacation to a remote Carribean island for a week. During the same week a plague of a mutated Ebola virus sweeps the Earth and drastically decreases the fecundity of all living women. Not only that, the viral infection also changes the genome of these women so that the daughters they give birth to will inherit this reduced fecundity. This means that far more than average of their fetuses will undergo abortions (or, in a somewhat kinder scenario, their female fetuses will be aborted more often than male ones).
Only this one woman and her daughters who were off in this Carribean island are safe from the viral plague. Also assume that the viral plague consumes itself within that fateful week. This woman and her daughters are now free to breed in a world where their reproductive potential far outstrips that of every other woman alive (and to be born of these women). Soon, almost every one on Earth will be related in some fashion to this one woman. Finally, when the last woman who was born to one of the matrilineal descendents of an infected woman dies, the non-infected Carribean tourist takes on the title of the new Mitochondrial Eve. Every human alive on Earth at that point in time is now related via the mitochondrial line to her.
But consider this new twist. Suppose a group of astronauts (men and women) were sent off into space during the infection week, and were thus not infected themselves. After many centuries in a Moon or Mars colony, they returned to Earth. At that time, suddenly, the title of Mitochondrial Eve would revert back to our own ME. The humans alive on the Earth at that time would all share their mitochondrial DNA with an earlier common ancestor.

Thus the title of Mitochondrial Eve depends very critically on the present human population of the Earth. As people die or are born, the title can change hands. Once a ME is established (via the death of a matrilineal line), further births cannot change the title. Further deaths can, however, transfer the title to a more recent woman. The older ME is still the common ancestor of all humans alive today on Earth with respect to matrilineal descent, but she is not the most-recent .... This is part of the reason why I said that each and every word of that definition was important.


http://www.talkorigins.org/faqs/homs/mtDNA.html
DNA (deoxyribonucleic acid) is the gigantic molecule which is used to encode genetic information for all life on Earth. DNA molecules consists of a long strand of base molecules arranged in the form of a double helix. The bases are adenine, guanine, cytosine, and thymine, often abbreviated as A, G, C, and T. What we ordinarily think of as "our" DNA, because it controls most aspects of our physical appearance, is also known as "nuclear DNA", because every cell in our bodies contains two copies of it in the cell nucleus.

Mitochondria (singular: mitochondrion) are small energy-producing organelles found in cells. Surprisingly, mitochondria have their own DNA molecules, entirely separate from our nuclear DNA. Most cells contain between 500 and 1000 copies of the mtDNA molecule, which makes it a lot easier to find and extract than nuclear DNA. In humans the mtDNA genome consists of about 16,000 base pairs (far shorter than our nuclear DNA), and has been completely sequenced (for one individual, at least; Anderson et al. 1981). What makes mtDNA particularly interesting is that, unlike nuclear DNA which is equally inherited from both father and mother, mtDNA is inherited only from the mother, because all our mitochondria are descended from those in our mother's egg cell (there may be exceptions to this rule, however; see below).

Consider the set of all women living today, then the set of all their mothers, and so on. Obviously, each set will be as small as or smaller than the previous set. Eventually the set will contain only one woman, who is known as "mitochondrial Eve". The mtDNA of all living humans is inherited from mitochondrial Eve.

Normally our mtDNA is identical to that of our mother. But, like all DNA, mtDNA mutates occasionally so that one of the bases (A, C, G, or T) changes to a different base. Because of these mutations, human mtDNA has been slowly diverging from the mtDNA of mitochondrial Eve, and the amount of mutation is roughly proportional to the amount of time that has passed. This means that similarity of mtDNA for any two humans provides a rough estimate of how closely they are related through their maternal ancestors. If they have identical mtDNA, they are fairly closely related, maybe even siblings. If they have very different mtDNA, it means their last common maternal ancestor lived long ago.

However, using the genetic difference to estimate the time of the last common ancestor is difficult, for a couple of reasons. One is that the rate at which mtDNA mutates is poorly measured. The other is that even if the average mutation rate is accurately known, some lineages will as a matter of chance accumulate fewer or more mutations than average.

After death, DNA starts degrading immediately. It is thought that under the most favorable conditions, some DNA fragments can survive for as long as 50,000 to 100,000 years. The Feldhofer Neandertal fossil, thought to be between 30,000 and 100,000 years old, was therefore pushing the limits for this kind of work. However initial testing of the fossil showed good preservation of amino acids, indicating that it might contain recoverable mtDNA.

Polymerase Chain Reaction (PCR) is a technique which can be used to create many copies of an initially small number of molecules. The researchers used PCR to amplify and extract many short strands of mtDNA from the Neandertal sample. By overlapping these, they were able to generate a sequence of 379 bases apparently from the Neandertal individual. To protect against errors and contamination, each base was extracted in at least two separate amplifications.

Krings et al. then compared this sequence against a database of 994 different mtDNA sequences from modern humans. For the sequence of mtDNA in question, humans on average differ from each other in 8 +/- 3.1 positions (the '3.1' represents one standard deviation). The greatest difference between any two modern humans was 24, and the smallest difference was 1 (because duplicates were removed from the database).

mitochondria live in the cell, but outside the nucleus, and have their own DNA. some researchers believe that it used to be a seperate organism, that became symbiotic with animal cells millions/billions of years ago, which help produce energy for the cell.

mitochondrial DNA is passed down from the mother only, since it was in the egg. The concept of the mitochondrial eve would be going back to your mothers mothers mothers mothers mothers mothers..... until you go all the way back to what could be considered the first human female.

mDNA/mtDNA is, as has been said, DNA residing in a mitochondrion within a eukaryotic cell. This DNA is different from other eukaryotic DNA in that it is circular and replicates separately from the rest of the eukaryotic genome. One important thing to take note of for mitochondrial DNA is that it (in humans) is always transmitted from mother to child (as no mitochondria from sperm survive). Thus, 'Mitochondrial Eve' is the original human from which all other humans (and mitochondria) came from.

Mitochondrial DNA (or mtDNA) is DNA found in the mitochondria of our cells. This is outside the nucleus where the bulk of our DNA resides that gives us most of our inherited characteristics.

We inherit our mtDNA pretty much entirely from our mothers only. (It is the mtDNA that was in the egg cell that formed us ... what little mtDNA is in sperm cells is discarded.)

This means that the mtDNA is passed as-is from mother to child (and passed on through daughters), with no modification from the father. So if it wasn't for mutations, we should all have *exactly* the same mitochondrial DNA as all the women in our maternal line, going all the way back through evolution.

However, mutations do occur. And so this mitochondrial DNA does change slightly over hundreds of generations. And so we can take any two humans on the planet, look at their mitochondrial DNA, and figure a pretty good approximateon of how far back they are related on their mothers' sides.

So by taking a wide sampling of many people from all different ethnicities and geographical locations on the earth, and looking at their mtDNA, we can get an approximation of the most recent common ancestor (MRCA) on the mother's side.

Geneticists call this woman "mitochondrial Eve" and have computed that she lived about 140,000 years ago.

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Incidentally, we can also do the same on our fathers' sides. Males pass their Y-chromosomes onto sons. Since this is not affected by the mother, the Y-chromosome is passed intact, except for mutations. (This follows the same rules as the passing on of last-name in our culture ... so all the males in your near or distant family who have the same last name as you have, also have the same Y-chromosome.)

Geneticists call this MRCA on our fathers' side "Y-chromosome Adam", and compute that he lived about 60,000 to 90,000 years ago.

So "Y-chromosome Adam" and "mitochondrial Eve" did not know each other (as they were separated by at least 30,000 years).

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Finally, don't get confused into thinking that "mitrochondrial Eve" was the only female human? She is just our most recent common matrilineal ancestor. She had a *lot* of people living at the same time as her ... but their bloodlines just have not survived to this day.

Mitochondria are the energy factories in our cells. They have their own DNA - mDNA - and they reproduce by cloning themselves within our cells. Since they reproduce clonally, the only way that variation is induced in their DNA is by mutation. Because they live within the cell but outside the nucleus, no mitochondria get carried along into sperm. The inheritance is strictly from the female side.
You can trace the geneology of two people whose mitochondria differ by a single mutation back through one or more generations to where the mutation hadn't occurred yet. Both branches of the family have the same mDNA at that point. If you follow this form through through all of the known variations in mDNA, it is consistent with all of present-day humanity being descended from a single woman about 140,000 years ago. That is mitochondrial Eve.
Since the human y-chromosome is inherited only along the male line, you can do a similar study with it. The y-chromosome Adam is 60 to 90,000 years past.

The theory of " mitochondrial Eve is laid out in the book, " The Seven Daughters of Eve ", by Brian Sykes.