Search Results for: gedmatch

When GEDmatch says your Parents are Related but they are not …

Sep18

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.

UPD can result in some dangerous medical conditions as per Science Direct (click here). Please see a professional genetic councilor if you suspect you have this.
Continue reading →

My talk about GEDmatch and more about GEDCOMs

Jun6

Finally! The video of the GEDmatch basics talk I did on May 26 for Verogen is now available. Best to view it full screen at youtube in order to see the images well.

Click here for the slides for that talk

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.

Continue reading →

A Really Basic Approach to Using GEDmatch

Feb18

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.

Recently I gave a talk for the Family History Fanatics at their Winter of DNA conference where I demonstrated how to use GEDmatch without worrying about segments. An approach that gets a lot out of the site without having to be a geek like me. The slides are here: https://slides.com/kittycooper/gedmatch-basics-2021

Here is a step by step of that very basic approach as outlined in the syllabus for my FHF presentation

1. Create a User ID and Upload a DNA raw data file, aka a “kit”

Click the image above to go to the video from Andrew Lee, of FHF, which shows you how to create a user id and upload your DNA raw data to GEDmatch.

Or read this blog post of mine which also has links to my other GEDmatch posts
https://blog.kittycooper.com/2019/02/genesis-basics-gedmatch-reinvented-part-1/

2. Once Logged in, your Dashboard Page is not Intuitive

The tools are in the right hand column and the resources you have uploaded are listed on the left. You can upload more than one DNA kit and multiple GEDCOMs. There is a help section on the top right.

This post from Jim Bartlett is a useful explanation of the home page, as is my basics post listed above.
https://segmentology.org/2018/05/01/first-time-at-gedmatch/

And here is what my beta test Dashboard looks like, an improvement? I think so.


Continue reading →

ALERT – Bug in the GEDmatch “Are Your Parents Related Tool”

Dec12

UPDATE: 13-Dec-2020: FIXED! The code had not changed but the environment had, so an initialization was different. Thus my analysis that it was always the first few chromosomes helped the programmer solve the issue.

 

The “Are Your Parents Related Tool” (AYPR) has been an enormous aid to those adoptees who discover that they were a result of an in-family relationship. Thus it is very distressing to have gotten a report from a reader that the tool is suddenly showing less cM that are ROH than it used to.

My investigation has shown that the first few chromosomes have segments that are not marked as ROH when they should be and were in previous versions. The programmer who can fix this told me that this bug goes back perhaps as far as this past summer He does have a working copy from July, but is in the middle of a major new project. Thus he may not be able to attend to this until later this coming week,

In the meantime, here is an example of how this looks so you can try to make your own estimate. The results for a child of first cousins was shown in my blog post about this tool (click here for that post).

ROH for child of first cousins,  buggy version on left, previous correct version on right (click for larger version)

To the left is how that looks now, while on the right is how it looked last year. Notice that the first three chromosomes on the left have not been included in the ROH listing. Also, the previous total was 215.3 which, when multiplied by 4, fit the first cousin scenario, now confirmed. The total without those first few chromosomes today is 126.8.

The cases from closer relations are even further off. A child of siblings had 744cM ROH last year but now gets only 465.6. A child from a father daughter pairing was was 750.4 and is now 547.9. In both cases the problem was the first four or five chromosomes were not having their ROH segments counted any more.

I will post an update on this blog post once the issue is fixed.

Tool to find common ancestors at GEDmatch

Jul4

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

GEDmatch has just released a tool for its Tier 1 (paid) members that will search for the common ancestor you have with your DNA matches on that site. This capability requires both you and your match to have uploaded a GEDCOM to GEDmatch and associated it with your kit. I just updated my 2015 blog post about using GEDCOMs at GEDmatch which explains much about them, so click here to read it. By the way, a GEDCOM is a text file that is formatted especially for genealogy programs; it lets you move the facts in your tree from one genealogy web site or program to another.

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 →