Recently I was asked whether there is a way to tell a full sibling from a half sibling. Sometimes the total centimorgans are low for one but high for the other. You expect to share about 2550 cM with a full sibling and 1700 with a half sibling; so which is it if you share 2100 cM?
The answer is that full siblings will share many fully identical regions (FIRs), over about 25% of their chromosomes. Half siblings will have no FIRs of any significant size. The exception being some small ones if their parents are from the same population group but still far far fewer than a full sibling.
Here is a comparison of my first eight chromosomes with my brother made at GEDmatch. The green bars are where we are fully identical, in other words we got the same segment of DNA from each of our parents there.
GEDmatch comparison of me and my brother (full siblings)
You can click on the image to see the entire display at GEDmatch that this was made from.
You do not have to be an adoptee to benefit from a class on DNAadoption.com – they have several one day classes which are introductions, explaining how to use your results, tailored to each specific vendor. They also have a longer basics course and many more advanced courses.
Diane, Tim Janzen, and Kitty at the 2013 Rootstech
The inimitable Diane Harman-Hoog wrote a blog post today announcing the two year anniversary of their classes. Along with Karin Corbeil and Rob Warthen, Diane has taken DNA adoption searches into the electronic age with online courses and much more information available on that site. The many success stories bring tears to my eyes. A few are here – http://www.dnaadoption.com/index.php?page=reunions and more can be found in the archives of the DNAadoption yahoo group.
I got to meet Diane at the 2013 Rootstech conference along with expert genetic genealogist Tim Janzen and many other wonderful people I had corresponded with via email. Needless to say I keep going back to that conference; of course, the location next to the great genealogy library in Salt Lake City has something to do with that also!
Rob Warthen has written some wonderful tools that benefit all of us genetic genealogists that are hosted over at DNAgedcom.com and are linked to from the DNA adoption site.