Your DNA contains a record of your ancestors, but you aren’t a carbon copy of any one of them. The particular mix of DNA you inherit is unique to you. You receive 50% of your DNA from each of your parents, who received 50% of theirs from each of their parents, and so on. In the chart below you can see how the amount of DNA you receive from a particular ancestor decreases over generations. If you go back far enough, there is a chance that you inherited no DNA from a particular ancestor.
The chart below helps illustrate how different segments of DNA might have been passed down from your grandparents to make your unique DNA. Assume each letter represents a segment of DNA. Things to notice are:
- Which letters get passed down to each generation is random (the fact that the letters spell names in this example is simply to help with the illustration).
- Not all of the letters get passed down.
- Just because a child doesn’t have a letter doesn’t mean that an earlier ancestor didn’t have that letter.
- Siblings can have different combinations of letters
In the example on the chart, your paternal grandfather has the unique DNA of ANDREW. He can pass down only 50% of his DNA to each child. In your father’s case, the “pieces of DNA” randomly selected to be passed on to him are represented by the letters DEW. At the same time, grandmother SANDRA provides the randomly selected segments ADR, which combine with her husband’s DEW to create your father’s unique genetic signature: EDWARD. Notice that not all of the letters from ANDREW and SANDRA get passed down to EDWARD.
Your father, EDWARD, has three children with your mother, whose genetic signature is ANGELA. EDWARD and ANGELA each pass 50% of their DNA, randomly selected, to each of their children, who end up with the genetic signatures GLENDA, GERALD, and REAGAN.
Again, the parents don’t get to choose which segments (letters) go to each child. And while having more children increases the chances of passing on more of your DNA, if you look closely, you’ll see that even with three children, not all of EDWARD and ANGELA’s DNA segments made it to the next generation.
This is a simplified example of how genetic inheritance works in all of us. By understanding how DNA is inherited, you can see how and why you have some DNA segments that match your relatives, and others that do not, why you may or may not have inherited DNA segments associated with a certain ethnicity, and why getting multiple people in your family tested can help discover more of your family’s genetic tree.
I have had fun learning about my own DNA inheritance, especially after I had a few of my family members tested. Next week check back and see how Irish I am compared to my family. You might be surprised-I was.
To learn even more about DNA inheritance and how AncestryDNA determines genetic ethnicity click here.
About Anna Swayne
Anna Swayne has 9 years of experience in the DNA genealogy world. At Ancestry, she leads efforts in developing education to help our community maximize their experience with AncestryDNA. She believes there is real power behind DNA and the story it can unlock for each of us. When she is not talking DNA you can find her hiking or cycling in the mountains or cooking at home.
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