Why You and Your Siblings May Be a Bit Different Ethnically

originally posted by 23 OCT 2014

I posted this morning on having my DNA tested through Ancestry.com and the results. I pointed out that even siblings will show different mixtures of ethnicities. &chumbler asked how this might be so I thought, "Well, there's a post waiting to happen."

I'm going to keep this very basic. First of all, I'm not geneticist and secondly, I've never even played one on TV.

Unless you are an identical twin, the DNA combination you have will be different from your siblings. This means that when you take a DNA test like the one on Ancestry.com, you are very likely to show different percentiles in ethnicity.

Think of it this way, Your mother has 100% of her own DNA. She passed 50% of it along to you. But, there remains 50% you did not get. Same with your father, you got 50% of your DNA from him. The mix of DNA you received will be different than your brothers and sisters. If it was the same, you'd look identical.

Let's look at this another way (and I'm hoping this makes sense). Mom got half her genes from her mom and the other half from her dad. We'll call her mother's genes A and her dad's genes B. You get half of your genes from your mother (a combo of A and B). There is randomness involved in what you get from her though (it's not a 50/50 split of Grandma's and Grandpa's genes) so you might end up getting more of the B genes than the A. If so, you are going to show more similarities to her father's family than her mothers. For example, let's say you got 31% of the genes she inherited from her father. That would leave only 19% of grandma's genes for a total of 50% of your DNA...remember, the other 50% is from your father's DNA and the same applies there. Now your sister is tested. She won't have the exact same DNA. She might have 28% in common with Grandma and 22% with Grandpa. If Grandma ancestry is traced back to Sweden and Grandpa's is traced back to Italy, you would likely show more traces of an Italian ethnicity on a DNA test and she could show more Swedish.

I know this is really basic but I hope it explains why you and your siblings could definitely show different ethnicity mixes on a DNA test.