Question

Will a DNA test still show I am a great granddaughter after 12/13 generations?

Answer 1

Stephanie, that depends on what kind of DNA test you take.  AUdna (Autosomal) does not go back more than 4 generations, but MTdna (Mitochondrial) goes back pretty much forever, but only along the female line, so it will trace through your mother, your maternal grandmother, her mother, etc.

Comments

Unfortunately Gaile, both sides are mixed male/female. I was hoping because I have relations to Henry V by both my paternal grand parents it might increase my chances. How do I find out if there are any relatives closer in my line that have  DNA records?

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I think "AUdna (Autosomal) does not go back more than 4 generations" is too restrictive. While there is no hard line, I think most people with 

• lots of matches, and with
• clearly no endogamy because the lines come from different places, and 
• reasonably complete trees 

easily find fourth and fifth cousin matches with a common ancestor and feel confident that that ancestor is the only recent common ancestor. When lucky, they even get triangulation. So that's ancestors back to 4th-great-grandparents, but that's 6 generations back. Not everyone has such a pristine situation, but some people do. If nobody did, there would be no reason for the triangulation requirement on Wikitree -- it would just be forbidden to confirm with auDNA past third cousins.

But regardless, that doesn't affect your main point -- 12/13 generations is way too far for AUdna.

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I essentially agree but would point out that for each generation there tend to be a number of sticky segments although fewer in number for each generation. So, it is possible to have a large segment survive 12 or so generations.  Unfortunately, going back that far also has a decreasing likelihood of having all links sourced, an exponentially more difficult task of eliminating alternate lines of descent, plus a highly unlikely of there being even one person with the same sticky segment when two are needed for triangulation.  In fact, the odds against this are even worse since any matching cousins will have to have been DNA tested and have their results on a platform with a chromosome browser and linked to their pedigree.

Long story short, although significantly large autosomal DNA segments can survive for 12 or more generations, it is so close to impossible to use it for confirmation purposes that one can simply dismiss it.

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Sorry Gaile but that's not true (that autosomal DNA isn't going further than 4 generations).

I can already see the damage done with this wrong statement as it's selected as the best answer in another question.

I have referenced to the work of Professor Itsik Pe'er in several G2G answers already (I wish I could easily reference it but I'm not able to search for it).

IBD segments go way beyond 4 generations and depending on the threshold you're applying (most DNA testing companies use 7 cM) you're going back to different time periods where the common ancestor is from.

I strongly suggest you watch Professor Pe'er's talk: Identity by descent in medical and ancient population genomics - if you eg. just go to 15:38 of his presentation you see a slide where Professor Pe'er shows that IBD segments between 0.5 to 10 cM do come from a common ancestor between 5 and 99 generations back.

Later on in the video he's also presenting his work on the "The Genome of Netherlands" project which shows estimates of the period where the common ancestor has lived for 1 cM brackets start from 1-2 cM (up to 2200 BCE) to > 7 cM (1500 CE onwards).

So in conclusion there is a possibility to identify common ancestors that far back however this would involve a large number of descendants of this common ancestor and looking at each potential permutation (comparison) between all people who are in such a triangulated group with a direct line to the common ancestor.

As there are for sure several possible lines between the common ancestor and the DNA tested people (meaning you're a descendant in more than one way) it can be assumed that there will be several different triangulated groups, not just one.