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  #21  
Old 3rd November 2017, 06:14 PM
Germanica Germanica is offline
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Originally Posted by GST View Post
The genetic distance chart is not accurate - on average, the number of generations should be increased by about a factor of 10, but average genetic distances are not very meaningful for evaluating mtDNA matches. So it would be best to delete the chart and explain how to evaluate matches.
I think the chart makes it pretty clear it's only an approximation and the number of generations are not absolute.
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  #22  
Old 4th November 2017, 12:58 PM
GST GST is offline
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Originally Posted by Germanica View Post
I think the chart makes it pretty clear it's only an approximation and the number of generations are not absolute.
The number of generations in the chart are wrong by about a factor of 10. That is a very poor approximation. But the real problem is that, because of the large variability in the accumulation of new mutations, there is no average number that is meaningful.

To use mtDNA results, one needs to look at the age of their subclade, count the number of extra mutations in their results, and estimate how recently they might be related to people who share those mutations. If your subclade is 6000 years old and you have no extra mutations, most of your matches are likely to be very distantly related, but if you have 5 extra mutations, your matches are likely to be much more recently related.

We also need to ask FTDNA to improve the way heteroplasmies and common mutations are counted in the genetic distance. There are cases of people who are very closely related who are not shown as FMS matches because FTDNA counts common heteroplasmies as multiple steps in the genetic distance.
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  #23  
Old 4th November 2017, 07:57 PM
Germanica Germanica is offline
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Originally Posted by GST View Post
The number of generations in the chart are wrong by about a factor of 10.
How do you know that? Can you provide a resource that supports this?
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  #24  
Old 5th November 2017, 12:56 AM
GST GST is offline
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Originally Posted by Germanica View Post
How do you know that? Can you provide a resource that supports this?
For the mutation rate, the 2009 Soares et al. paper "Correcting for Purifying Selection: An Improved Human Mitochondrial Molecular Clock". Here is the key text: "The substitution rate for the entire molecule was 1.665x10-8 substitutions per nucleotide per year, or one mutation every 3624 years."

Behar et al. 2012 discuss the extreme variability in the rate at which mutations occur in different lineages, which they call "clock violations".

I'm a project administrator for several mtDNA haplogroup projects and have also looked extensively at the full sequence samples in GenBank, and there are many samples in subclades that are several thousand years old that have no additional mutations. One example is U5a1a1 which is estimated to be about 7000 years old and has been found in ancient remains dated to about 5100 years ago. There are over 150 samples of U5a1a1 that have no extra mutations, and they could share a common maternal ancestor with their exact matches more than 200 generations ago.

You can check the age of your subclade and then check to see how many additional mutations you have. You should exclude at a minimum 309.1C, 315.1C, 522.1A, 522.2C because they are extremely common and not useful for evaluating matches. A16182c, A16183c, 16193.1C(C) and C16519T are excluded from Phylotree and also have limited value. If your subclade was not included in the age estimates in the Behar et al. 2012 paper, you can calculate the average mutation rate for people in your subclade and use the spreadsheet from the Soares et al. paper to estimate the age of your subclade.
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  #25  
Old 5th November 2017, 01:33 AM
GST GST is offline
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Here is another way to look at the results, for my subclade U5a2a1 which is estimated to be about 6000 years old, there are 185 full sequence samples in the U5 project and in GenBank. On average people in U5a2a1 have 2.26 extra mutations but the distribution is shown below, where 15 people have 0 extra mutations, 39 people have 1 extra mutation, etc. If you are one of the people with several extra mutations your matches are likely to be more recently related.

#mut, number of people
0, 15
1, 39
2, 64
3, 32
4, 26
5, 4
6, 3
7, 2

Last edited by GST; 5th November 2017 at 01:36 AM.
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  #26  
Old 5th November 2017, 02:07 AM
dna dna is offline
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This is the point where we disagree, a mutation could have occurred and then (later) the ancestral state could have returned. We think stability, but there was none.

mtDNA tree is full of back mutations.

I have read current papers, and yes clearly there is no more talk about parallel mutations (convergence). However, I am not convinced that mtDNA changes are so trivial that www.phylotree.org would not list any parallel mutations (at least I could not see any).

I am backing out of this discussion, as I need to learn more from up to date literature. Maybe one day someone will write a complete explanation of mtDNA for genetic genealogists.


Mr. W
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  #27  
Old 5th November 2017, 10:16 AM
georgian1950 georgian1950 is online now
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Originally Posted by dna View Post
This is the point where we disagree, a mutation could have occurred and then (later) the ancestral state could have returned. We think stability, but there was none.

mtDNA tree is full of back mutations....

Mr. W
Mr. W, I think you are 100 percent correct. I have certainly seen examples that appear to belie the notion of mutations being thousands of years back. Within a few months I hope my research will be able isolate some examples of mutations taking place within hundreds of years instead of the thousands of years generally thought.

Jack Wyatt
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  #28  
Old 5th November 2017, 10:36 AM
GST GST is offline
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Originally Posted by dna View Post
This is the point where we disagree, a mutation could have occurred and then (later) the ancestral state could have returned. We think stability, but there was none. mtDNA tree is full of back mutations.
Back mutations do occur in mtDNA but they are relatively infrequent compared to the total set of mutations that define a haplogroup, and when you test the full sequence different subclades will not converge in the same way that yDNA STR can converge. Convergence is really only a problem when using a small number of markers to compare results, especially in the yDNA 12 and 25 marker STR tests, but less of a problem when you test more markers. Convergence can be a problem with the HVR mtDNA test, for example, multiple haplogroups can be CRS in the HVR region, but FTDNA also tests additional coding region SNPs as part of the HVR test.

There are certain mtDNA markers that do back mutate very frequently and they should not be included when evaluating matches.

There are also cases in which the precise structure of the mtDNA phylotree can be uncertain because of multiple reversions at markers that mutate frequently, but this is a reason to discount these markers when building the tree. I don't think it is useful to use markers 152, 195 etc to define "paragroups" as is currently done in Phylotree. So back mutations can be a problem, but testing the full mtDNA sequence or testing the full Y sequence basically solves the problem.

Last edited by GST; 5th November 2017 at 10:45 AM.
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  #29  
Old 10th November 2017, 08:35 AM
soonerdi soonerdi is offline
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So confused

The more I read about mtDNA, the more confused I become. I thought the mtDNA would help me better understand my mother's maternal line, but I was told by an administrator that the mtDNA traces the family of my mother's maiden name. That just doesn't make sense, as my maternal grandmother has no dna from my mother's maiden name. I understand that you learn your haplogroup, but how does the test rule out Native American ancestry? Thanks for any help!
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  #30  
Old 10th November 2017, 08:59 AM
Biblioteque Biblioteque is offline
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Native Americans have their own Haplogroups which will rule you in or out.

MtDna traces your mother's LINE, not her name, back in time.

From Roberta Estes, a list of NA Haplogroups. Hope this helps.


https://dna-explained.com/2013/09/18...l-haplogroups/

Last edited by Biblioteque; 10th November 2017 at 09:11 AM.
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