Wednesday, December 7, 2011

Mystery Cousins: Autosomal DNA Testing

   I recently received the results of my autosomal DNA test.  The test is part of a larger project that I am working on and not all the other samples have been tested yet.  So, I was happily surprised and confused to find that the results of my DNA matched other people.  I now have 28 fourth or fifth cousins I never knew I had.  These are 28 people with no obvious connections to me.  Not even a surname match.  My first thought was that these are 28 false positives.

Blarney Castle - McCarthy Built

   Everyone has 46 chromosomes, 23 from each parent.  Two of these chromosomes are the sex chromosomes, x and/or y.  The remaining 44 are the autosomal chromosomes.  When comparing the results, the larger the matching segments the closer the relation.  In October of this year, FTDNA announced that they had made changes to their matching algorithm to reduce false positives.  With that in hand, I will move forward with some confidence that these 28 people are my cousins.

   This creates 28 research projects.  Maybe it will be fewer depending on how many of the 28 want to collaborate.  We just have to find our common 4th great grandparent.  No problem, right?

   I should be able to weed out the false positives (if there are any) by getting back to the origins of these other folks.  My 4th great grandparents were either in Italy or Ireland and more specifically, outside of Naples or in the middle of County Cork.

   Some of these 28 ‘cousins’ have also included surnames.  There are quite a few Irish names and no Italian names listed.  This will help narrow the research work.

   I have 28 emails to send – wish me luck.

1 comment:

  1. Hey Mike,

    I was googling for DNA testing and genealogy and your blog popped up. Very informative and interesting.

    Anyway, you may remember when I asked you to research my McPartlan ancestors who may have lived in Worcester. I know of a possible distant cousin who lives in Springfield, and I want to compare her DNA with my mother's. I believe that they are second cousins once removed and according to the FTDNA site, the chances that they find a relationship is between 90-99%.

    I haven't tried any of the DNA testing companies, so I'm not familiar with how they work. Do you know what are the chances of a false positive with relatives that are second-third cousins? The impression I get from other web sites is that false positives can happen once you get past 4th or 5th cousin.