Second cousin DNA tests are my favorites. You share enough DNA with a second cousin to be really useful for genetic genealogy. When someone matches your second cousin, you know which of your four pairs of great-grandparents they are related to, so it identifies the family line they are on.
Of course not all second cousins are created equal. Due to the vagaries of DNA inheritance some may have inherited more from the mutual great-grandparents and some less. For example, my Dad shares 608 cMs with my second cousin John from his mom’s side and only 389 cMs with my second cousin Dick from his Dad’s side. I discussed this variability in a recent post about how to tell the relationship from the shared DNA.
I thought I had no chance of a second cousin on my maternal side because my German-born mother’s parents were both only children, or so I thought. When I started researching my family history back in the 1990s, by asking questions of my aunts, I found a family secret or at least a story I had not known before. My great-grandfather Benedict Reiner had gotten the innkeeper’s daughter pregnant and then left town; he moved to Munich and a few years later married my great-grandmother. Further discussions had revealed that the child’s name was Xavier and he had visited occasionally so the families had been in touch. This was not enough information to find him or his family, since he had his mother’s surname, but thanks to GENI.com, I found them by accident. That story was a blog post earlier this year – http://blog.kittycooper.com/2016/01/thank-you-geni-com/
Now for even more good luck, my brother had a trip to Germany scheduled for a few months later so he was able to take a day off and actually meet our newly found cousins. Here is the picture.
Even more exciting for me, we convinced them to test autosomal DNA at Family Tree DNA. We tested the oldest, my half second cousin Edeltraud, the grandmother of my correspondent Katharina. Today the results came in and I am so very happy!
The reason this was important to me, other than wanting another second cousin for comparisons, is that my Ashkenazi percentages come out higher than my brother at all the different companies. My mother is from a mixed marriage – her mother, Fanny, was Bavarian Catholic, half sister to Xavier, and her father was German Jewish. If these ancestry composition estimates are correct, then my brother would have more Bavarian DNA from our grandmother than I do. This might show up in the amount of shared DNA with Edeltraud. In other words, it looks like we inherited unequal amounts of DNA from each maternal grandparent.
The expected shared centimorgans with a half second cousin are about 106 (half of the 3.12% for second cousins) and for my two aunts, who are half first cousins once removed, about 212 (half of the 6.25% for first cousin once removed). These numbers are from the ISOGG wiki see http://isogg.org/wiki/Autosomal_DNA_statistics
Above is the summary of our family comparisons to Edeltraud. [UPDATE:Changed the totals to count only those segments over 7cM since the original totals listed, now on the far right, included a few smaller triangulating segments].
My theory works, my brother Shipley has significantly more shared DNA with our half second cousin. Furthermore, it seems proven by the autosomal DNA matching that Benedict was the father of both Xavier and Fanny. Some family stories are true.
This is very interesting and I will need to read it again more slowly to take in the calculations so they will be useful to my own research.
Hmmm .. this is getting too much for me I think.. what is the purpose of all this may I ask ? Other than perhaps furthering the science of DNA??
The purpose is to use DNA to further my genealogy research which is my idea of fun!
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