You get 50% of your mother’s DNA and 50% of your father’s DNA. As to which 50%, that’s an exciting roll of the dice. Autosomal DNA tests can tell you about the last 5 generations (30 people not being swabbed!) in your family which is why these tests are favored among genetic genealogists.
Though there are 29 other people involved in my autosomal sample, I’m interested in Sara J. Taylor who is my 3rd great-grandmother and just outside of the predicted reach of the test. She was 100% Sara. Ramonsita was 50% Sara. Domitila was 25% Sara. Grandma is 12.5% Sara. Mom is 6.25% and I am 3.125% Sara J. Taylor, or at least I am theoretically. Is that enough information to shed some light on her family? Maybe, maybe not. I have heard that some people get lucky.
Right now there is a very interesting thread (FF results -problems with Mexico ancestry?) on the Family Finder section of the FTDNA Forums. His relative got the kind of Native American percentage I would hope for and a good Berber percentage too, but the OP is confused about how the test revealed some Russian in his family. They probably were Russian Jewish people who converted a long time ago. That’s the cool thing about genetics; you never know what you’ll find.
Here are two excellent articles I found thanks to someone on the FF Forum that discuss the difference between genealogical relationships and genetic relationships: Everyone Has Two Family Trees – A Genealogical Tree and a Genetic Tree and How Many Ancestors Share Our DNA? So Sara J. Taylor may turn out to be just my genealogical ancestor rather than my genetic ancestor (well, only in terms of autosomal DNA since I have her mitochondrial DNA). Or she might have passed more of her autosomal genetic material than I thought:
“As a final note, there is an interesting effect of the larger recombination rate in women; you are, on average, slightly more closely related to your maternal line (your maternal grandmother, your mother’s maternal grandmother, etc) than you are to you paternal line (your father’s paternal grandfather, etc)… You are about 30% more likely to be genetically related to your maternal-line ancestor 10 generations ago than you are the corresponding paternal-line ancestor (14% vs 11%).”
I’ll find out around Halloween. Trick or Treat?