World Families Forums - How can one make an educated guess about MRCAs?

Welcome, Guest. Please login or register.
September 21, 2014, 10:50:53 PM
Home Help Search Login Register

+  World Families Forums
|-+  General Forums - Note: You must Be Logged In to post. Anyone can browse.
| |-+  Newby Questions
| | |-+  How can one make an educated guess about MRCAs?
« previous next »
Pages: [1] Go Down Print
Author Topic: How can one make an educated guess about MRCAs?  (Read 1611 times)
Schwarzburg-Sondershausen
Member
**
Offline Offline

Posts: 20


« on: March 10, 2012, 10:19:57 PM »

We recently got Y-DNA marker numbers from FamilyTree DNA and although the company has not told us what haplogroup our family member belongs to, we are pretty confident that it is a Q1a3a Native American lineage. We connected to one somewhat close match. I'm curious if there is a formula to reckon how far back these two gentlemen's most recent common ancestor actually lived.

14 25 13 10 14-18 12 12 12 14 16 32 16 9-9 11 12 27 14 20 29 14-14-15-19 10 11 19-23 17 16 19 17 38-38 12 11

12 25 13 10 14-19 12 12 12 13 16 32 16 9-9 11 12 27 14 20 29 14-14-14-15 10 11 19-23 18 16 18 17 37-38 12 11
Logged
Terry Barton
Administrator
Guru
*****
Offline Offline

Posts: 1662


« Reply #1 on: March 10, 2012, 10:40:54 PM »

"somewhat close" is not what I'd call this.  I count a Genetic Distance of 12 0n 37 markers - 3 times what we typically use to call someone "related".  If you simply count matching markers, it's still only a 29/37 - 2 times what we typically call related.

I'd guess that you are talking a "coupla thousand" years - but I didn't crunch the numbers vs an accepted calculator.

If you want more formal analysis, here's Dean McGee's calculator.  Try it with all 3 mutation rates and you'll see how much a single assumption can affect the estimate when you are this far from a traditional "related"

http://www.mymcgee.com/tools/yutility.html
« Last Edit: March 10, 2012, 10:41:48 PM by Terry Barton » Logged
Schwarzburg-Sondershausen
Member
**
Offline Offline

Posts: 20


« Reply #2 on: March 10, 2012, 10:52:27 PM »

Thanks, Terry. We were told our relative's Y-DNA was weird and they were going to do a backbone test on it. This was the closest match and it isn't even close. Bummer
Logged
Terry Barton
Administrator
Guru
*****
Offline Offline

Posts: 1662


« Reply #3 on: March 10, 2012, 11:03:17 PM »

Thinking about your question in a different light - if this comparison was a typical "match" with a genetic distance of 4 on 37 markers (33/37 match) - the "time" to most recent common ancestor (tMRCA) would be about 6-20 genereations ago.  (that's approximately the confidence interval for 10-90%  - or 80 % of the time.  If you wanted to get 90% of the possibilities - the range would be about 4 to 22 generations

At 25 years per generation with the 10-90% range, that would be 150-500 years ago.  At 30 years per generation, that would be 180-600 years ago.  My own paternal line is 33 years per generation back the first 12 generations - which would make the estimate 200-670 years ago.

Changing to 90% of the possibilities, the range could be as low as 100 years to more than 700 years ago

I generally encourage folks to talk in terms of "sharing a recent coomon ancestor" which is a 33/37 or 61/67 match - or better.  I personally try to avoid discussions about time to Most Recent Common Ancestor - as they can be really confusing
Logged
Terry Barton
Administrator
Guru
*****
Offline Offline

Posts: 1662


« Reply #4 on: March 10, 2012, 11:05:15 PM »

That's great that you are going to get a backbone test.  Hopefully, it will help your research.  Do join your Haplogroup Project - as those researchers usually have a good insight
Logged
Schwarzburg-Sondershausen
Member
**
Offline Offline

Posts: 20


« Reply #5 on: March 10, 2012, 11:15:12 PM »

Okay, now...that doesn't make it seem so distant. Would you say its within the realm of possibility that their most recent common ancestor could have lived 300 years ago? Considering that their ancestors were probably Lipan Apaches who lived in Texas pre-1690, I imagine their lifespans may have been on the short side. Or is this just wishful thinking?
Logged
Schwarzburg-Sondershausen
Member
**
Offline Offline

Posts: 20


« Reply #6 on: March 10, 2012, 11:21:16 PM »

Here's another relative of mine to consider:

14-21-14-10-12-16-12-12-12-13-11-30-19-8-10-11-11-27-14-21-31-13-16-17-18
14-21-14-10-15-16-12-12-11-13-11-30-19-8-10-11-11-27-14-21-31-13-16-17-18

Would I be right to think these guys are actually fairly closely related?
Logged
thetick
Member
**
Offline Offline

Posts: 20


« Reply #7 on: March 11, 2012, 12:49:17 AM »

If you have FTDNA results there is a calculation tool called TiP.  Look for the TiP icon when viewing your results.  Below is FTDNA's info on TiP:

http://www.familytreedna.com/faq-tip.aspx
Logged

YDNA: R1b-SRY2627
MtDNA: H5a1f
Schwarzburg-Sondershausen
Member
**
Offline Offline

Posts: 20


« Reply #8 on: March 11, 2012, 01:00:46 AM »

If you have FTDNA results there is a calculation tool called TiP.  Look for the TiP icon when viewing your results.  Below is FTDNA's info on TiP:

http://www.familytreedna.com/faq-tip.aspx

Thanks
Logged
Terry Barton
Administrator
Guru
*****
Offline Offline

Posts: 1662


« Reply #9 on: March 11, 2012, 10:59:14 PM »

Initial posting pair of results with a Genetic Distance of 12 on 37 markers and a match of 29/37:  the odds are extremely low that they will share a common ancestor at 300 years.   No one I know would consider this to be an indication of recent common ancestry and if you were to come up with additional test results and paper trail proof that this pair actually do have shared ancestry in 300 years - you'd be cited as the most extreme case ever found

Second pair of results have a genetic distance of 4 on 25 markers or a 23/25 match:  Again, this is not an indication of recent shared ancestry.   It is theoretically possibly (and I do know of one similar case that had a GD=4 on 25 markers) that these men share a recent common ancestor - but it is very doubtful.  The first thing I'd do is upgrade both men to 67 markers and see how they compare

Standard matching is GD=4 or less on 37 markers or GD=6 or less on 67 markers.  Comparisons at 25 markers are "iffy" and not even worth doing at 12 markers unless you know the paper trails connect.

Why don't you read through the relevant sections of DNA the Smart Way at www.worldfamilies.net/smart
« Last Edit: March 11, 2012, 11:10:04 PM by Terry Barton » Logged
Arwunbee
Member
**
Offline Offline

Posts: 47


« Reply #10 on: April 08, 2012, 02:54:02 AM »

I'm looking for a basic rule of thumb, nothing too fancy, based off GD only.  I thought I read somewhere for 67 markers, every 1 of GD could mean about 100 years back?

E.g. GD of 19 for 67 markers, say 1900 years MRCA very approx?
Logged

Map of L44 subclade (of U106): http://g.co/maps/9xswy
WebMaster
Administrator
Old Hand
*****
Offline Offline

Posts: 108



« Reply #11 on: April 09, 2012, 05:09:02 PM »

Take a look at this Blog entry which I call  "Don't Count Mutations":

http://www.worldfamilies.net/blog/16609
« Last Edit: April 09, 2012, 06:51:20 PM by webmaster » Logged
Pages: [1] Go Up Print 
« previous next »
Jump to:  


SEO light theme by © Mustang forums. Powered by SMF 1.1.13 | SMF © 2006-2011, Simple Machines LLC

Page created in 0.06 seconds with 18 queries.