|Screen shot from AncestryDNA results|
There are plenty of resources at AncestryDNA for a user to learn about and understand the results, and those testing at Ancestry should definitely upload a family tree, which makes this process much more useful for all. However, AncestryDNA does not have a chromosome browser.
GEDmatch so I could compare his results with the results I have from FamilyTreeDNA and I can compare the DNA results using the chromosome browser there.
For more information about GEDmatch, visit the FAQ pages or the main page of the GEDmatch Wiki. It is a free resource though donations are accepted. (If you have a membership at Legacy Family Tree Webinars, watch this Legacy Family Tree webinar to learn more about GEDmatch.)
The top two matches for this cousin are my father-in-law (HH) and my husband (SH).
And of course because we're talking Ashkenazi Jewish DNA (an endogamous population), he also matches my mother-in-law (AH), but with much less DNA.
|Screen shot of GEDmatch results for cousin G.S.|
From the ISOGG Wiki: Endogamy is the practice of marrying within the same ethnic, cultural, social, religious or tribal group. In endogamous populations everyone will descend from the same small gene pool. People will be related to each other in a recent genealogical timeframe on multiple ancestral pathways and the same ancestors will, therefore, appear in many different places on their pedigree chart. Endogamy can be the result of a conscious decision or cultural pressure to marry within the selected group but also occurs as a result of geographical isolation (for example, in island communities).
GEDmatch tells me that:
GS and HH share 524.5 cM with the largest segment of 73.0 cM. (First cousin once removed shares about 6.25% of DNA, or about 425-440 cM.)
GS and SH share 292.8 cM with the largest segment of 43.7 cM. (Second cousins share about 3.125% of DNA, or about 213-246 cM)
GS and AH share 66.4 cM with the largest segment of 13.9 cM. (No known relation.)
The total number of cM is different between AncestryDNA and GEDmatch because AncestryDNA removes many of the smaller segments in calculating its total cM. (I believe their algorithm recognizes certain endogamy.)
In the GEDmatch results, the greater than average matching DNA is due to endogamy.
Also, this makes me disinclined to try to figure out how my husband and his parents are related to their DNA matches unless there is more than, say, 100 shared cM and certainly more than 20 cM in the largest matching DNA segment.
I will share what the GEDmatch chromosome browser looks like in an upcoming post.