Archives

What does shared X DNA really mean?

Jan6

Since familytreeDNA added X chromosome matching to their family finder, all my favorite bloggers have been writing about how to use it. There is a list of their terrific articles at the end of this post.

Of course those of us who have many family members tested at 23andme have been working with the X chromosome for a while and have some thoughts on how useful it might or might not be.

  1.  Smaller matches on the X will usually be too far back to find the relationship because the X chromosome does not get recombined when a father passes his only X chromosome on to make a daughter. Thus segments can stay together longer in time.
  2. A match on the X can eliminate many ancestors from an autosomal match BUT a small match on the X can be from a different line so this is not guaranteed.
  3. There seems to be less recombination on the X. I have heard of cases where a child got an unrecombined X from their mother. In my own family, the number of recombined segments is quite small. So it seems to me that on the female to female line the X behaves like a sluggish autosome and is not quite as actively recombined as the other chromosomes. [UPDATE 11-May-2018: the X has been shown to have a normal amount of recombination for any chromosome by a citizen science study done by Blaine Bettinger, click here for blog post by Leanne Cooper summarizing this.]

Less recombination examples

Because our maternal line (1/2 Ashkenazi, 1/2 Bavarian Catholic) is from two different population groups, my brother and I can learn which maternal grandparent we got our X DNA from just by looking at the ancestry composition for that chromosome at 23andme:

XchromCompare Continue reading →

Finding Distant Relatives with Autosomal DNA Testing

Jan14

Maybe you tested your DNA to prove or disprove a genealogical theory. Or maybe you tested to check on your health risks or carrier status. But now you see all these possible 3rd to 5th cousins in your family finder or relative finder lists and you wonder if you are related and if you can find that relationship. Perhaps you contacted a few and had almost no responses.

DNARelativesSampleSYes you are probably related, but without both of you having a good paper trail you would be most lucky to actually find that relationship. It is likely to be further back than suggested if your ancestors were at all endogamous. Just living in the same location for a few hundred years can lead to much inadvertent intermarrying and more common DNA than degree of relationship would expect. So autosomal DNA testing is no genealogical shortcut. Some of the people you contacted already know this, so if they saw no common surnames or places on your profile they may have lost interest.

So be prepared before contacting those likely 3rd to 5th cousins.

  1. Have an easily readable pedigree chart in both PDF and online format (GEDmatch can do the latter, more on GEDmatch later)
  2. Another good tool is a list of about 12 generations of ancestors by place name. Much easier for a possible relative to scan.
  3. Do some reading on the basics. UPDATE 9-sep-2018 See my article – http://blog.kittycooper.com/dna-basics/
  4. Try to talk some close relatives into testing so you have more data to work with
  5. Last but not least, make a decision on how much time you want to devote to this project … warning it can be addictive

If you want to do the minimum, then scan the localities and surnames of these possible cousins and contact the ones with surnames or place names in common with you. Indicate in your message that this is the reason for contact. Include the URL for your pedigree or family site and offer to send the PDF files. Include your email address if you are using the 23andme messaging system. The more directed the contact, the more likely you will hear back. I recently went through and cancelled some of my early invitations and send new improved ones on the lines above and got four new shares.

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Common Ancestors Can Be Very Far Back

Dec24

So far I am finding that the common ancestors with Dad’s DNA matches at both 23andme and FamilyTreeDNA are much further back than predicted. We have found the MRCA for only those distant cousins with good paper trails and perhaps even a tree at GENI like we have.

Most of these matches are only one or two segments and the longer the segment the more likely it is to be a real match with a discoverable common ancestor. I actually found a new 5th cousin of mine through DNA, Dad’s 4th cousin once removed. She has a one segment match of 17.14 CMs and 2849 SNPs in common with Dad and our common ancestors are in the 1700s at farm Fatland in Etne, Hordaland, Norway (online resources for Etne research listed at familysearch.org)

23andme shows you all your 7cm and larger matches but many genetic genealogists think anything less than 10cm is suspect. My view is that if Dad’s match is also a match with either me or my brother (n.b. frequently the match is for fewer SNPs and CMs in the next generation) then it is real, even at 6cm. As you can see in the chart, we have found many common ancestors with smaller than 10cm matches. GEDmatch lets you look at even smaller segment matches with specific people as does Family Tree DNA.

Here is a summary of the most recent common ancestors in Norway that I found for Dad with some of his DNA matches:

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Making a spreadsheet of autosomal DNA matches

Nov15

It is very interesting to look at the overlapping DNA segments of one’s matches in order to figure out where they may have come from and how they might be related. It also helps with tracking these relationships and comparing the results from different sources. Personally I know when someone matches my 2nd cousin Dick that the relationship is on dad’s father’s line.  My next task will be to start diagramming the possible relationships based on who matches whom among all our new distant cousins.*

To find the DNA segments where you match another person at 23andme that you are sharing with you put your cursor on “My Results” in the very top menu bar and then click on “Ancestry Tools” at the bottom of the second column of selections to get the page that lists Family Inheritence: Advanced. Within this function you select the person to compare to on the left and all those to do it with on the right. So typically I take a new person and compare them to me, my brother and my Dad; then various cousins. You need to select the table version to get the numbers shown in the spreadsheet below.

Here is how I track overlapping segments. I make one spreadsheet for each person I am looking at, sorted by chromosome, segment start, segment end and length.  I use the same columns as the 23andme table view of my genome shares but add one column at the beginning marked with a P or M (paternal or maternal side match) whenever I know it. Then I add a column for the most recent common ancestor (MRCA), one for known relationship (when found), and another one for notes where I put comments like “same match with Kitty, no match to Dick, matches Jane elsewhere).

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Ashkenazi Genetic Pile Ups?

Nov8

Well I thought I had found a real cousin on the German Jewish side due to a few common surnames but no luck finding the relationship yet. Sadly there is a large match on our X but the common surnames are not on a branch where X could come from. Of course one of the problems in German Jewish genealogy is that all but a few prominent families had no fixed surnames (they used their father’s name) until 1813/14.

Even worse she mainly matches me on segments that are what I call “Ashkenazi Pile Ups” or locations where there are well over 30 people matching me but not my Dad for more than 5cm.  By comparison I notice only one such pile up on my 100% Norwegian father’s matches at chromosome 9, at about 80,000. But that will be the topic for another post.

These are the three pile ups my new distant cousin matches:

Chromosome 2:  45 matches for this segment at 23andme

150.1 163.3 9.9CM

Chromosome  4: 80 matches for this segment at 23andme

some start at 18.1 and some end at 25.0

19.4 24.8 7.2CM

Chromosome X: about 30 matches for me, 50 for my brother…. hmmm

a few are longer than this

123.4 137.8 14.1CM

For those of you who are wondering where to find this data on 23andme you can download all the segments that match yours with the name of the donor (most will be anonymous) by going to “ancestry labs” under ‘My Results” and clicking on “Countries of Ancestry.”  Scroll down the page to the long blue button where you can download a CSV of all your matches. [updated 27 dec 2013 – n.b. you can get this data and more  by using the http://DNAgedcom.com site to do the downloads]

There are a few more pile ups in my and my brother’s matches than these …

Continue reading →