I was just on Ancestrys website and I was looking at their DNA page and I found this:
How It Works
Applying DNA science to family history
What you inherited
There’s only one YOU — you’re unique. Yet you share common connections to the family in your past. Those connections are found in your DNA.
Think of DNA as the internal set of blueprints that your body follows to make you who you are. Much like a fingerprint, each person’s particular combination of DNA is unique.
But, unlike that fingerprint, your DNA was passed down to you by your ancestors. And that makes it an unparalleled tool for family history research.
Why DNA runs in families
Here’s how it works: you get half of your DNA from your father and half from your mother. They, in turn, got their DNA from their parents, who got it from theirs, and so on. While the particular combination inherited from a single set of parents makes each person unique, the shared genetic details of family members are what link you back to people born throughout history.