GEDmatch.com has a wonderful free tool called Are Your Parents Related which I have previously blogged about (click here). This function looks at your raw DNA results for long stretches where you have the exact same DNA on each side of a paired chromosome, known as Runs Of Homozygosity (ROH). In other words where you got the exact same DNA from each parent. I always check this for unknown parentage cases.
When you have ROH segments, it is expected that your parents are related. However there is one other way this can happen: in very rare cases, you can get a whole or partial chromosome from only one parent. This is known as uniparental disomy (UPD).
An example of UPD on chromosome 6 from the Are Your Parents Related (AYPR) tool.
How can you tell that this is the case? Likely it is UPD when you have only one ROH segment and it is for the whole chromosome like the image above or for one arm of a chromosome (from or up to the centromere). In the less than one hundred cases I have looked at, I have seen UPD only twice. Once a whole chromosome as shown above and once the long arm of chromosome 14.
GEDmatch, a DNA tools site, was originally created to compare GEDCOMs, a function you can still use it for. A GEDCOM is a plain text file of your family tree formatted so that any genealogy program can understand it. Click here for the wikipedia entry explaining this in more detail.
In my talk I emphasized that it is best to upload a privatized GEDCOM with no more than 10 generations of ancestors then connect it to the DNA test for that person. This will help you use the relative matching tools. I promised in the presentation to explain how to create a GEDCOM. So here are a few of the many ways.
It has been two months since my husband died and I am still not back but there is so much interesting genealogy and DNA news that I am making the effort to blog today. Forgive my lack of original thought; my brain is not working well yet, other widows call it “grief brain.”
DNA expert panel at the 2019 SCGS Jamboree: L to R: Brad Larkin, me, Tim Janzen, Angie Bush, David Dowell, and the organizer Alice Fairhurst
First of all, my favorite local conference, the Southern California Genealogical Society Jamboree has been restructured as a two weekend virtual event. This coming Friday and Saturday are about DNA and yes I managed to record a talk on finding cousins which explains some of my favorite techniques at the major sites. Next weekend is the Genealogy portion, again on Friday and Saturday. Plus, as always, there are some free events; for example, Monday next week has virtual round tables and I will be hosting one. Click this URL for more information about all this conference: genealogyjamboree.com
23andme has come out with an interesting report on the genetic basis for why some people lose their sense of smell with COVID. Click here to read it (it requires you to log in)
Finally GEDmatch has released their updated prettier site. You have the option to use the new site which still has a few small bugs or the old, familiar, but clunky site. Yes the changes are mainly cosmetic and making help more available. As soon as I have some energy I will blog about them. In the meantime be sure to try the new site and send bug reports to firstname.lastname@example.org
GEDmatch.com is about to get a face lift. Many have complained that it is not intuitive and does not offer enough help for a newcomer. The new site hopes to correct some of that; I am helping with the beta test now; it sure is prettier!
Why use GEDmatch and what is it? Well it’s a free 3rd party site of tools where you can upload your DNA test results and compare them with those from people who have tested at other companies. Plus there are many analysis tools, some available nowhere else. These include GEDCOM (family tree) comparisons, including yours to your DNA matches.
Whenever I get a new good-sized DNA match, I try and figure out how we are related. Ancestry and MyHeritage both have clever tools that search your tree and the trees of other users to come up with the likely relationship. Of course both you and your match have to have a family tree connected to your DNA on those sites for that to work.
My father’s DNA matches with matching ancestors, first run
The new tool found nothing on my mother’s side. She was German and half Jewish. There are almost no Germans at GEDmatch and my one known half 2nd cousin on there has no tree uploaded. As to the Jewish side, very few have their trees far enough back to meet mine. I need to get a few of my known 3rd cousins to upload GEDCOMs.
The above listing, partially repeated below, shows all the common ancestors my first run of this tool found for my Norwegian-American father using the default settings on the form. I have cut off the first 3 columns on the left which have the kit number, match name, and email address for privacy; also that makes the image readable on this page!
Let’s look at the rest of the columns for my Dad’s top match. Clicking the tree icon would take you to the user profile information. The cM shared are listed next; 40.3 is match that can be anything from a 4th to an 8th or even more distant cousin. Then the name of the possible shared ancestor, first in my GEDCOM and then in my match’s GEDCOM; either one can be clicked on to go to that person’s tree entry. The 8G is how many steps down from that ancestor my Dad is. If you click that, you see a descendant list from that ancestor in your tree. Notice that his match is also 8 steps down, so in the same generation. Subtract one to get the cousin level so this is a 7th cousin. Continue reading →