Archive | January 2014

What does shared X DNA really mean?

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.

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

My contest for a free pass to RootsTech 2014

One lucky reader will get a free pass to Rootstech 2014 this coming February (an educational event for the howtos of using technology in family history research), since I will be an official rootstech blogger. So my idea was to award it to whomever comes up with the best question for me to ask Spencer Wells at the conference. I am expecting to have a private interview with him, video recorded and posted here. So send me your questions via my contact page by January 30th.

It was Well’s book, Deep Ancestry: Inside The Genographic Project, that sparked my interest in population genetics and genetic genealogy. After I read it, I did the original NatGEO DNA test. Then I transferred the results to FamilyTreeDNA.com but my mitrochondrial DNA was too deep in the past to satisfy my genealogy cravings. Soon thereafter I heard about 23andme and tested there. Twisted the arms of many family members and relatives to get tested, including my father, whom I had tested by both of those sites. In the process I read lots of books and blogs. The marriage of genes and genealogy known as genetic genealogy had me firmly hooked.

Read on for more about all the things I have enjoyed reading to expand my understanding, n.b. favorite blogs are in the column on the right towards the bottom. Continue reading