How Autosomal DNA is Passed Down (Inherited)

This Video from the University of Utah explains how we inherit DNA.

We inherit a 50% of our DNA from each parent.  That also means there was 50% of our parent’s DNA we didn’t inherit.  The same is true for our parents. They received 50% of their from their parents. That means that while we might expect to have received exactly 25% of our DNA from each of our grandparents, it how much will vary, in some cases, alot!

Due to the randomness of how DNA is passed down down, you may only receive  26% from your maternal grandmother and 24% from your maternal grandfather. It still adds up to 50% that you got from your Mom. But on your Dad’s side, you may have only received 10% from your paternal grandmother and 40% from your paternal grand father. It still adds up to 50% that your received from your father.

Take a look at the picture. You can see how you received different amounts of your DNA from different grandparents and great grandparents.

This also explains why your siblings, other than identicals, have different ethnicity estimates and look similar but different than you.  You each received some of the same DNA and some different DNA from their parents and grandparents and so on.