Archives

Full versus Half Sibling DNA Matches

Apr29

Recently I was asked whether there is a way to tell a full sibling from a half sibling. Sometimes the total centimorgans are low for one but high for the other. You expect to share about 2550 cM with a full sibling and 1700 with a half sibling; so which is it if you share 2100 cM?

The answer is that full siblings will share many fully identical regions (FIRs), over about 25% of their chromosomes. Half siblings will have no FIRs of any significant size. The exception being some small ones if their parents are from the same population group but still far far fewer than a full sibling.

Here is a comparison of my first eight chromosomes with my brother made at GEDmatch. The green bars are where we are fully identical, in other words we got the same segment of DNA from each of our parents there.

GEDmatch comparison of me and my brother

GEDmatch comparison of me and my brother (full siblings)

You can click on the image to see the entire display at GEDmatch that this was made from.
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DNA day sales end today!

Apr26

Dna-splitNational DNA day on April 25 celebrates the day that Crick, Watson, et al published their papers on the structure of DNA. There is an article in Wikipedia about it at https://en.wikipedia.org/wiki/DNA_Day

Both Ancestry.com and Family Tree DNA have been celebrating this date with sales of autosomal DNA test kits that end today. So buy a few!

23andme did not have a sale, but has sent a $50 off coupon out to people who have already tested there as a mother’s day sale or gift and that is good through next Sunday.

See my DNA testing page for a comparison of the sites. Remember that if you test at ancestry you can transfer those results to Family Tree DNA (click here for my post on that with the details)

Ancestry Composition Comparisons: a Case Study

Apr16

Discovering where your ancestors came from is one of the more popular reasons to do a DNA test but the current ancestry composition algorithms have a long way to go. Sometimes East Asian ancestry is actually American Indian and South Asian might be gypsy or Indian Indian. Scandinavian might be British or North German and British and Irish might be Scandinavian.

Most efforts to analyze the deeper roots of your ancestry are based on samples of modern populations who self report four grandparents of a single ethnicity plus some public databases and a few ancient samples. Since each company relies greatly on their own databases of tested people, it is not surprising to see differences in their predictions.

My brother's Ancestry as shown at DNA.land

My brother’s Ancestry as shown at DNA.land

Since my brother is tested at all three companies I thought I would post the images of what each company sees in his DNA as well show the new report from DNA.land and a few from GEDmatch (both using his uploaded Ancestry.com DNA data). We are confident of our recent ancestry: 50% Southern Norwegian, 25% Bavarian German and 25% Ashkenazi.

The new DNA.land report is shown above, Hmmm, only 16% Ashkenazi.

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Patience please with the new 23andme

Mar25

A while back I did a blog post explaining how to navigate the new 23andme (click here to read that). A number of my complaints in that post are now fixed. Most importantly, the ability to search for people to compare on the DNA Relatives > DNA page is there plus a table view which gives the numbers.

I cannot agree with the genetic genealogists who are abandoning 23andme due to the problems with its change over to their new web site, as well as the perceived lack of response to genetic genealogists. 23andme never made a secret of the fact that they are in this to research the genetics of various medical conditions. That is fine with me, as my extended family has many medical issues to look into, most, thankfully quite minor. They did make some nice tools for genealogists to attract more users into their database, but we have never been their primary concern.

Disovery23andmeS

While I do recommend Ancestry.com DNA testing for most new testers, many of my cousins want the medical information and so are willing to pay the extra for 23andme. It also has the best ancestry composition of the big three.

Personally though, my main reason for being patient and staying with 23andme is that I have found so many Norwegian and Norwegian-American cousins there (over 30) while only one or two at the other companies. Maybe we Scandinavians just have more genetic health issues. I also like the ability to compare cousins to each other and look at the ancestry composition by chromosome (although that is currently gone on the new site).

While 23andme is changing over to their new system, those of us with kits still on the old system have struggled to contact and share with our new matches. Initially we could not send shares to new matches so had to message them and ask them to send us a share. Thankfully that is fixed.
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Another Triangulation Success, Another Etne Cousin

Mar4

So what is the opposite of the saying when it rains it pours? How about the sun is not only shining but there are rainbows!

When you keep extensive spreadsheets that include the common ancestor for segments of DNA that triangulate, you sometimes have quick success with a new DNA relative.

I recently shared my Norwegian 3rd cousin’s kit with Shelley on 23andme. She has a large X match with him that I am still working on. His maternal side from Rogaland is not related to me that I know of.

Naturally I always compare a new DNA relative to everyone else possible. I was surprised to discover that she shares a small bit of DNA with my Dad and my brother that triangulates with a known fourth cousin and her sister. Synchronicity … these are the same cousins mentioned in my previous post about my X segment from Ve and Fatland.

Etne Fjord, VE farm at distant left

Etne Fjord, Ve farm at very distant left hand side

So I emailed Shelley and told her that she shares a small (6cM) segment that we know comes to us from our ancestor Aamund Bjørnson Tvedten (Ve) 1772-1842 so perhaps we share one of his ancestors. She replied back, all excited, wow my great-grandmother is Anna Wee (Ve).

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