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Author Topic: Can mitochondria become obsolete?  (Read 1955 times)

Offline annie123

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Can mitochondria become obsolete?
« on: 13/12/2014 00:06:01 »
if a woman has only brothers, sons and grandsons does this mean that her mitochondria doesn't get passed down and  is no longer in her descendants? Does this make the only semblance of immortality she can have impossible?


 

Offline evan_au

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Re: Can mitochondria become obsolete?
« Reply #1 on: 13/12/2014 10:06:23 »
Quote from: annie123
does this mean that her mitochondria doesn't get passed down?
Mitochondria (and their Mitochondrial DNA) is passed from mother to child.
  • So a woman's daughters and her sons will all carry (a subset of) her Mitochondrial DNA
  • A woman's brothers and sisters will carry a very similar set of Mitochondrial DNA (if they have the same mother)
  • A woman's sisters will pass on a very similar set of Mitochondrial DNA to her nieces and nephews
  • If a woman and her sisters have only sons, then a very similar set of mitochondrial DNA will still be passed down by her Aunts and great-Aunts 

Quote from: annie123
the only semblance of immortality she can have
The other chromosome which is passed down the female line is the X Chromosome, which is passed down from a woman to both sons and daughters, and also to grandchildren. If a woman has only sons, they will pass on the X Chromosome to their daughters.

But in reality, a woman passes down all her other chromosomes to her children too, whether she has sons or daughters (although they are slightly mixed up during Meiosis, so her children get a mix of genes from all their grandparents). This is far more genetic information than is present in Mitochondrial DNA.

And even if a woman has no children of her own, her brothers, sisters, aunts and uncles will pass down large fractions of the same genes to their children. So this is a form of "genetic immortality".

In today's society, cultural inheritance has considerable impact too, so a woman can influence others culturally, even if they are genetically unrelated. This can be a far wider impact than just her biological children.
 

Offline annie123

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Re: Can mitochondria become obsolete?
« Reply #2 on: 14/12/2014 01:09:02 »
Forget sisters/daughters - the case I am thinking of has no female immediate relatives/progeny. Aunts on mother's side died childless. From what I understood, mitochondria of a particular person cannot be passed down by a male so it would seem that this female's particular mitochondrial genome would die out. Yes, he DNA carries on but the genome linking her to ancestors and the beginnings of humanity would disappear. Her sons would not pass it on. Their sons would have their mother's line. ??
As for cultural influence - I wasn't concerned with that - just the physical link with the past and the future being continued, or, as it seems, discontinued.
 

Offline evan_au

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Re: Can mitochondria become obsolete?
« Reply #3 on: 14/12/2014 05:50:23 »
If there are no female relatives, then that mitochondrial line will die out, as you say (apart from hypothetical possibility of paternal mitochondrial inheritance).

However, I am puzzled why the focus on mitochondrial DNA? Could this be a matter of obsolete technology and terminology?

When genetic sequencing was much more expensive than today, it was common to just sequence the mitochondrial DNA*. This is because the mitochondrial DNA is fairly small, and there are multiple copies of it in every cell.

So if you read older genetic studies, you will see a focus on Mitochondrial DNA; mitochondrial DNA was often used as a proxy for the nuclear DNA - and the language used possibly gave the impression that the mitochondrial DNA represented the entire DNA.
But if you read more modern studies of inheritance, you will see that they do whole-genome sequencing, using modern high-throughput sequencing machines. This recovers far more of a person's genetic inheritance (or their tribe). And the story is much more complex than the picture you would get from just mitochondrial DNA.

In the end, all humans inherit their Mitochondrial DNA from a woman dubbed "Mitochondrial Eve". So this Mitochrondrial DNA line will not become entirely extinct until the last human dies.

*Mitochondrial sequencing is still sometimes done today if a sample is badly degraded, since Mitochondrial DNA is still the easiest DNA to decode.
 

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Re: Can mitochondria become obsolete?
« Reply #3 on: 14/12/2014 05:50:23 »

 

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