Using Segment Sizes in DNA Relationship Predictions

Apr13

Segment sizes matter for predicting the closeness of a relationship. That is because inherited DNA chunks get divided up with each generation’s recombination, becoming smaller over time. It has often puzzled me that none of the DNA relationship calculators take that into account. The total centimorgans (cM) can be similar for lots of different relationships. Click here for my post on telling half siblings apart from aunt/uncle/niece/nephew relationships by using segment sizes.

Click here for Ancestry’s explanation of how they predict relationships and here for the article at 23andme. Neither mentions segment sizes.

Click this image for my slides demonstrating the DNA painter relationship calculator

My favorite calculator has long been the one at DNA Painter where the table is based on Blaine Bettinger’s collected data and the probabilities are by Leah Larkin based on the Ancestry white paper. It can work from a percentage or a cM value and lights up just the possible relationships in its table. Clicking on any table entry gets a histogram of frequencies.  I have slides showing how nicely it works, done for a recent talk about 3rd party DNA tools for the SCGS jamboree. Click the image above to see those. That video should be available to attendees from the web site genealogyjamboree.com

Recently a calculator was published at DNA-SCI which includes segment sizes by asking for the number of segments. I have used it for a number of closer relationships and have been very impressed with its results.
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How Related Are Ashkenazim?

Feb28

Eight of the ten fully Jewish kits I have access to showed related parents in the “Are Your Parents Related”  (AYPR) tool on GEDmatch. I am wondering if this level of relatedness (about a 4th cousin) is generally true among Ashkenazim and other endogamous populations. Or perhaps the GEDmatch parameters need some tweaking?

Sample related segment from a Jewish kit in AYPR

Sample related segment from a Jewish kit in AYPR

Also a number of married jewish couples I know have discovered that they share a DNA segment. Personally I share 11 cM on the X with my late husband even though I have only one Jewish grandparent. Most testing companies show me as about 30% Jewish.

I can understand that when people live in the same general area for generations, one could easily marry 3rd and 4th cousins. I also know that in the past, cousin marriages were not uncommon among Jews.

I invite all tested fully Jewish people to run that free tool at GEDmatch and then fill out my form on the next page. Please fill it out even when they are not showing as related to help with my statistics.

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Genetic Genealogy Fiction

Jan30

Aloha from my Hawaii cruise. Apologies to all of you for not getting any blogging or work done while at sea. My brain kept telling me I was on vacation!

One thing I like to do when cruising is to read fiction by the pool or at night. My new favorite mystery author is Nathan Dylan Goodwin who has a series about a forensic genealogist as well as a wonderful new series about a fictional genetic genealogy company called Venator.

I read the second Venator book first, The Sawtooth Slayer, which Nathan was kind enough to send me for a review. It stood up well, even though out of sequence. I then lent it to a friend who is neither a genealogist nor a DNA tester to see if it was an enjoyable read for her and others like her. She really liked it! She told me that now she is interested in doing her family history and maybe even a DNA test! So by all means give this to any friend who is interested in understanding what we do.

Next I had to get the first book, which I really liked also. The characters were particularly engaging. Then of course I started working my way through his other series, which is more genealogy based but still quite enjoyable.

Kitty drinking coffee at Kona Joe’s on the big Island near Kona

Ancestry Now Divides Your Matches by Parent

Dec1

Even if you haven’t been carefully assigning sides and relationships to your DNA matches, Ancestry will now try to assign sides for you! As with the recent Sideview feature (click here for that blog post), it uses Parent 1 and Parent 2. However you can use the blue Edit Parent link to change them to Paternal and Maternal, if you can figure out from the matches or communities which is which.



If you click on DNA Matches in the DNA menu as shown above you go to a new page like the one for my matches that I show here (click it for a larger version). It separates your matches into parent 1 and parent 2 (or maternal and paternal if you have assigned those) plus Both sides and Unassigned. Newer matches since April will always be unassigned, as well as ones it cannot figure out (click here for Ancestry’s explanation). You can see more surnames or communities by clicking on the blue View more in each panel. Clicking on All matches in the top menu bar will take you to the usual match page but now each match will have a side, both sides or unassigned listed underneath their relationship in the list. There are a few examples below. You can click on By parent to get back to this interesting new page. Clicking View matches in the first box for Parent 1 or any designation will show you your match list with matches from just that side.

I had delayed blogging about this fun feature because it was initially buggy and they took it down briefly. Also it is still in Beta test, so perhaps not everyone has it yet. Sadly there are still a few problems, so take your results with a grain of salt. Not surprisingly, people from endogamous populations are mainly out of luck with this new tool.

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This Blog Began Ten Years Ago Today

Nov2

On this date, ten years ago, I started this blog. I used to write a new post once or twice a week but I have slowed down since the death of my husband in 2020, to about once a month. At least I am still blogging.

I started this blog as a way to keep track of my own genealogy and DNA research so that I no longer needed to bombard my cousins with emails. Also I was hoping to teach them how to use DNA to assist their own genealogy research. My first post was about my Dad’s Y DNA test results.

Sample extract of my compact chromosome mapper at GEDmatch

It turned out that my articles were often helpful to others. My focus was frequently on unknown parentage. I even wrote a number of tools to assist people with that research. My most popular tool, Ahnen2GED, turns an ahnentafel list into a GEDcom. Another program, my compact chromosome browser was picked up by GEDmatch, a tools site I blog about frequently. An exciting moment for me was when a screenshot of it appeared on TV in an episode of CeCe Moore’s Genetic Genealogist 

When this blog became very popular (much to my surprise), I started to be asked to give talks about genetic genealogy, first at local groups and then important conferences like RootsTech and the Southern California Genealogy Jamboree. This month I will speak about unknown parentage for the North County DNA interest group on November 19. That group is close to my heart since it was there that I first heard CeCe Moore speak in 2012 and got inspired to do more with my family’s DNA test results.

Thank you all for reading my blog.