Ancestry Composition

Among the new genealogy tools at 23andMe is the Ancestry Composition.  This tool presents the DNA that you have that is very similar to the DNA of people in other parts of the world.  Because both of my parents have tested at 23andMe, I can show my DNA broken down into the half from my mother and the half from my father.

23andMe
Ancestry Composition for Me
in relation to both of my parents

Both my parents are essentially of European descent.  My father's tree is mostly Colonial American with a splash of German and Irish.  My mother's tree better illustrates my composition.  My 22% British and Irish from my mother's side is most likely because of my maternal grandmother, Jeannette ODonnell.  All of her ancestors trace back to Ireland by the mid 1850s.  My 11.7% Ashkenazi is likely from my paternal grandfather's father.  What makes me think this?  Look at my mother's Ancestry Composition by chromosome.

23andMe
Ancestry Composition by chromosome for Jody's mom

On her 23rd pair of chromosomes, XX, a woman carries no genetic information from her father's father.  IF one paternal grandparent was Ashkenazi and the other was not, then we can tell from this analysis that it was the paternal grandfather who was Ashkenazi because there is no Ashkenazi inheritance on the XX chromosomes.