Re: Help = Ancestry DNA .. is it worth looking below 2nd Cousin if no proof in trees or known relatives? #dna


kdomeshek@...
 

There is a very informative article that explains the autosomal DNA pitfalls of endogamy, which include Ashkenazim.  The author is Jennifer Mendelsohn.  The title is:  No, You Really Don't Have 7,900 4th Cousins".  There was an earlier reply on this thread from someone who noted that distant cousins could be connected genealogically with a higher incidence of success, if they involved his non-Jewish side.  That was logical.  The non-Jewish population is comparatively heterogenous, such that shared lower levels of cMs are statistically more likely to be from traceable genetic matches.  To avoid the "false positives" of untraceable matches, I use a soft cut off of 150 shared cMs, when dealing with a 100% Jewish person.  However, if a lower-level match has a shared long block of 20 or greater, it is probably not a coincidence.  A shared long block with 20 or more cMs is an indicator of a common ancestor, because it is statistically unlikely to have occurred randomly.  A lot of shared short blocks, which total 150 or below, is a potential indicator of random endogamous DNA that is recirculated among insular, intermarrying populations, such as Ashkenazim.  Instead of being from a single common ancestor, the pattern of many shared autosomal short blocks could be explained by multiple ancestors who existed further back in time, potentially during the patronymic period, which predates the effective generational range of the autosomal test.  (Contrary to the misleading advertising, the autosomal test is good for about 3 generations, 4 if you are lucky.  Beyond that, the signal-to-noise ratio of this test becomes unreliable.  The patronymic period ended in circa 1800 AD, up to 8 generations ago.) 

Ken Domeshek
FTDNA Project Administrator
Damesek, Braverman, Kartorzynski, Sinienski

Join main@groups.jewishgen.org to automatically receive all group messages.