-
28th August 09, 01:13 AM
#22
 Originally Posted by gilmore
Actually, there is a way to tell how far back in time your and your close YDNA's matches' most recent common ancestor lived.
Family Tree DNA has a software tool that will give you an estimate as to the probability of the number of generations that separate you from each of your matches. "...FTDNATiP™ calculator which takes into account our new University of Arizona mutation rate study information. " http://www.familytreedna.com/my-ftdn...ftdna-tip.aspx
It is expressed like this, an example of one of my close matches and me:
"In comparing 37 markers, the probability that Mr. XXX and Mr. AAA shared a common ancestor within the last...
generation is 2.72%
2 generations is 9.72%
3 generations is 19.9%
4 generations is 31.56%
5 generations is 43.32%
6 generations is 54.25%
7 generations is 63.84%
8 generations is 71.93%
9 generations is 78.53%
10 generations is 83.79%
11 generations is 87.89%
12 generations is 91.05%
13 generations is 93.44%
14 generations is 95.22%
15 generations is 96.55%
16 generations is 97.52%
17 generations is 98.23%
18 generations is 98.74%
19 generations is 99.11%
20 generations is 99.37%
21 generations is 99.56%
22 generations is 99.69%
23 generations is 99.78%
24 generations is 99.85%."
We can see that the 50th percentile is crossed between five and six generations. Therefore, it becomes more likely than not---or probable--- that our most recent common ancestor was at least five or six generations ago. The number of years in a generation for men varies from culture to culture, from society to society, but the usually accepted figure is 27 years, so we see that that was some 135 to 162 years ago, or around the period starting in 1847 and ending in 1874. Thus, our most recent common male ancestor probably lived in the early 19th century or earlier. While this fact is not in itself dispositive of a whole lot, it can be an important clue. And that is what much of genealogical research is, following clues until we arrive at harder and harder facts, and get a more and more conclusive picture of who and where our ancestors were, and what they were doing.
In this case, the other man knows from his research when his patrilineal ancestor came to America from Europe, and which city he came from. This tells me where and within what period of time it might be useful for me to do further research, starting with my oldest documented patrlineal ancestor I am sure of, and working backward.
Also, YDNA testing can sometimes show with amazing exactitude---with precision that increases as more and more men test--- the geographic location where the mutation of the marker(s) that distinguishes their YDNA from others' occurred, and how long ago it occurred. In other words, it is now sometimes possible to say, e.g., that "It is more probable than not that Mr X, Mr Y and Mr Z descend from a common male ancestor who lived on the island of Harris 250-300 years ago."
I have to say that as far as I know, the estimates of mutation rate, especially in "coding" and there fore naturally selected regions of the genome, is a topic of pretty hot debate right now. I'd be chary of pinning too many statements of *Truth* on estimates.
Also, and I don't know the answer to this.... exactly WHICH regions of the Y chromosome are sequenced to provide the ancestry information. There's still a huge amount of debate over the spontaneous mutation rate, but whatever the case, estimates are in the range of a single mutation per 100 - 500 generations.
Here's a very low estimate, I know the second author on this paper..
http://www.ncbi.nlm.nih.gov/pubmed/14691732
Here's a stunningly high estimate
http://dienekes.blogspot.com/2009/08...tion-rate.html
Four base substitutions in thirteen generations? Wow, that's four point mutations in 250 years.. I haven't read the actual paper, I don't know how they actually got tissue from 13 generations back...
It's also pretty clear that the Y chromosome does not mutate evenly across all loci.
http://www.sciencedirect.com/science...cfeb20edae7dc1
In summary, again, I'd be chary of putting too much weight on the TIMING of things, as "determined" by yDNA testing.
However, one thing you said is spot-on, for sure... "with precision that increases as more and more men test"
I'd also like to very slightly edit another phrase that you wrote, to make a point...
In other words, it is now sometimes possible to say, e.g., that "It is more probable than not that Mr X, Mr Y and Mr Z descend from a common male ancestor who lived on the island of Harris 250-300 years ago."
sometimes...yes. Sometimes, no.
I quite like the way you phrase this...
In other words, it is now sometimes possible to say, e.g., that "It is more probable than not that Mr X, Mr Y and Mr Z descend from a common male ancestor who lived on the island of Harris 250-300 years ago."
It's clear that you're talking about estimates, and understand that generation times can vary. As long as the discussion is about "estimates" I'm good to go! 
And you make a good point. As the cumulative data set widens, the accuracy is only going to get better....though it will still always be an estimate.
-
Similar Threads
-
By brandycr in forum Miscellaneous Forum
Replies: 24
Last Post: 2nd May 07, 05:22 PM
-
By switchblade5984 in forum Miscellaneous Forum
Replies: 5
Last Post: 1st June 06, 04:16 PM
-
By Graham in forum General Celtic Music Talk
Replies: 0
Last Post: 8th September 05, 04:44 PM
-
By Graham in forum Contemporary Kilt Wear
Replies: 32
Last Post: 28th August 05, 12:21 PM
-
By akaussie in forum General Kilt Talk
Replies: 2
Last Post: 18th January 05, 02:26 AM
Posting Permissions
- You may not post new threads
- You may not post replies
- You may not post attachments
- You may not edit your posts
-
Forum Rules
|
|
Bookmarks