Ancestors that share our dna -- big suprise

[thetick]

As another reference point, I have a 5th cousin 2X removed confirmed with genealogy and a common ancestor born in 1700. We are a 66/67 ydna match and do NOT match at 23andme. He has not tested with Family Finder.

[mkdexter]

6th great grandfather I believe.. The other person didn't put a location but the name matches. Don't know about the other one.

There is also a Y111-3 that is a generation farther back (7th great grandfather), no FF match either.

[shandy4473]

Interesting

True indeed Matt. The two Y-DNA 111 matches, what was there exact relationship?

If I may ask?

Thanks
Steve

[mkdexter]

As you see you can not expect a YDNA match to also match in Family Finder. I know of Y111-2 matches that are not Family Finder matches.

If you think about how the YDNA test works, it is based on mutations causing differences between two tests. In a perfect world there would be no mutations thus, no differences.

In contrast, an autosomal test is expected from the very onset to be different the next generation and in fact it does not take too many generations to see recombination of DNA dissolving many if not all of the matching similarities.

The autosomal DNA test is not comparing an ancestor to a descendant, it is comparing two people who possibly share the same segment patterns as detected by SNP testing. Having in-common segment matches is heavily dependent upon the randomness of recombination working in ones favor. Had the test been looking at ancestor and descendant it would be a little easier to track the DNA down each generation than trying to find people who have segments with the same admixture patterns.

The timeframe of finding a non-persistant segment match is only about four to five generations, much sooner than that expected timeframe of a mutation occurring in many of the DYS marker comparisons.

So while one test is expected to match for a long time, but may not, the while other test is not expected to match for very long at all, sometimes it does and hence two completely different results most of the time.

Matt.

[shandy4473]

Thanks

Quote:
Originally Posted by shandy4473:

"And where in the textbooks or documentation is 90% chance not 3rd cousin, 99% not 2nd cousin or closer. Only around 50% chance of having segment share if you were 4th cousins, about 15% if you were 5th cousins, and less than 5% chance if you were 6th cousins or more distant. Less than 50% does not imply safe to assume anything. Sources please!!!!"

The thread was closed so here are some sources that exist!

http://www.familytreedna.com/faq/answers/default.aspx?faqid=17#628

and
http://www.genetic-inference.co.uk/b...-share-our-dna

Thanks thetick!!!! I closed that thread to prevent it from swelling into an argument that would distract from the group. My original point taken and twisted into statements and assumptions I wasn't making by a usual party.

[Geneadict]

Thanks

Thanks, was going to post reply to closed thread with link to FTDNA FAQs and ref #26. RF FAQs include similar %s, though differ a little on some of the more distant relationships listed. Of course thread was closed and have no desire to argue with or badger anyone, but rather help when possible. Guess I need to leave that to others some of the time. thks

[thetick]

Quote:
Originally Posted by shandy4473:

"And where in the textbooks or documentation is 90% chance not 3rd cousin, 99% not 2nd cousin or closer. Only around 50% chance of having segment share if you were 4th cousins, about 15% if you were 5th cousins, and less than 5% chance if you were 6th cousins or more distant. Less than 50% does not imply safe to assume anything. Sources please!!!!"

The thread was closed so here are some sources that exist!

http://www.familytreedna.com/faq/answers/default.aspx?faqid=17#628

and

http://www.genetic-inference.co.uk/blog/2009/11/how-many-ancestors-share-our-dna