Search This Blog


Tuesday, December 2, 2014

DNA Differences and Siblings

Mom with her brother's DNA in yellow
If you have read any amount of blog posts or articles on genetic testing for genealogy you have encountered over and over again the concept that you should test as many people as possible. Particularly when doing an autosomal DNA tests.  I like to say go broad or go home which causes eye rolls around my house. 

The basic idea, for those of you not sure, is that you ideally want to test as many people who are willing, from as many different lines and generations as possible, enabling you to get the most coverage of your known family available to you through DNA.  Mainly, because family members may not have the exact same DNA passed on to them from their ancestors.  This is true to cousins especially the more distant you are.

Cousins, yes! Makes sense right?  Your most recent common ancestor was several generations away from you so of course there would be big gaps in shared DNA.  What I never, ever, dreamed of seeing was how important it is to test siblings.  Needless to say I am now scrambling to convince my husband’s siblings to test.  Which I think will happen about the same time they start serving ice water in hades.  I won’t bore you here with the large number of relatives who think I have lost my mind on this subject, but I bet you all can commiserate on some level.

In August I convinced my dad’s sister and brother as well as one of my mother’s brothers to give DNA testing a try. They dutifully took the tests when they showed up a month later from FTDNA.  I was optimistic that these tests would help break down a few walls and shed new light on some genealogy path overgrown with brush.  While I was at it I had my uncles do Y-DNA tests too.  Might as well right?  I am still waiting on those results which should be here any day.

dad with his sister in yellow
and brother in blue
My mom and her brother were what I expected from siblings, and then some.  They shared nearly equal amounts of DNA across all chromosomes.  Pretty typical right, when you assume that they had the same father and mother they should share a significant amount of DNA.  All I could think of was “wow, those are some strong genes."

Now, my dad and his siblings were completely different.  While they did fall within the suspected sibling percentage range there were large segments that my father did not share with his siblings.  What made that exciting was when their results hit the pages I was able to connect with lines that would not have been possible with just my dad’s results. (Plus if you look closely you can see where likely common cross overs took place during recombination on some chromosomes.)

To make it even more fascinating I compared my dad’s ethnic charts to his siblings.  Neither of them have ANY of the British Isle markers that my dad has.  They both are heavy on what I know through the paper trail is the Northern and Western European (aka German and Swiss) lines of the family.

Yep, this is going to lead to some interesting debates in the family about who takes after who I am sure.  Now I am waiting impatiently for my great aunts results.  She is the last living sibling of my paternal grandmother.  At 94 I am just thankful she agreed to do a test, and even more thankful that my dad’s sister facilitated it.  When I have her DNA I will be one step closer to my Irish and German immigrant families.  Plus maybe even more relatives…

Dad's ethnic breakdown

His brother's and sister's
ethnic breakdown


  1. Like you, until recently I thought having just one child in a family was fine. And then I began to read and play with the data a bit more, and I realized what a gold mine there was in there. Especially with being able to reconstruct portions of my deceased father's DNA (since I have my mother and his brother and his mother to use as controls). To further that I have convinced my 3 sisters to test (but none of them have actually completed the test to mail it back yet ... grrr).


    In the mean time I have begun work on testing my husband's side of the family. HIs sisters, his father, his maternal uncles ... the list is growing there as well.

    I know you do not think me crazy, nor I you. Our respective families however ......

    Elizabeth E.

    1. Nope we are not crazy. You can now show them this though... ;)