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How Much DNA Do We Share With Our Ancestors?

Do you want to know how much DNA you would share with your ancestors? In this post, learn how much DNA you likely inherited from the past several generations of your ancestors.

As a general rule, we can expect to share about 50% less with each ancestor as we go back a generation. There is much more to the story, however, and you will learn everything that you need to know on this topic below.

We often become interested in how much DNA we share with our ancestors because of DNA testing. Or, we might see a physical resemblance between ourselves and our ancestors in old photographs.

How much DNA did you inherit from your parents?

Each person inherits almost exactly 50% of their DNA from each of their parents, meaning that everyone shares 50% of their genome with their mother and 50% with their father.

You inherited half of your mother’s DNA and half of your father’s genes, too. About half of both of your parent’s DNA did not get passed down to you.

In centimorgans, a unit of measurement for expressing genetic distance, we would share about 3400 centimorgans (cMs) with each of our parents. If you have taken a DNA test and compare your DNA to your parents, you might find that this number doesn’t appear to be exactly 50% – it’s only due to slight variations in testing.

How much DNA did you inherit from your grandparents?

We share approximately 25% of our DNA with each of our grandparents, but this number can vary. You inherited between 18-32% of your DNA from any of your four grandparents.

The reason that the exact percentage of DNA that you inherited from your grandparents can vary is because of the way that DNA is inherited. As I mentioned earlier, you only inherit 50% of your mother and father’s DNA.

The exact 50% that you inherit from each of your parents is selected randomly in a process called recombination. The effect of recombination is that we don’t know exactly which DNA you’ll get (i.e. more from Grandma than Grandpa, etc).

All we do know is that you will always inherit a substantial amount of DNA from both your maternal and paternal grandparents. In centimorgans, we would expect this amount to be 1300-2300 cMs.

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How much DNA did you inherit from your great-grandparents?

On average, a person inherited about 12.5% of their DNA from all eight of their great-grandparents. This is only an average, and it is normal for someone to have inherited as little as 4% to as much as 23%.

Of course, if you inherited a higher amount from one great-grandparent, it would mean that you share less with another. The actual amount of DNA that you would share with a great-grandparent would vary greatly, but it wouldn’t be higher or lower than the range I mentioned in the previous paragraph.

Did you notice that it is possible to have inherited as low as 4% of your DNA from a great-grandparent? This is very important to note, since as we move down in generations we may share very small amounts of our DNA with our ancestors.

In fact, it is possible to have inherited no DNA at all from some of our ancestors after a certain number of generations. You will see more on exactly when this might occur this further down in this post.

The broad range in DNA inherited from a great-grandparent is one of the reasons that we might seeing very small amounts of DNA shared with second cousins, especially half-second cousins. We can see this information on our DNA match lists if we have taken a DNA test.

How much DNA did you inherit from your great-great grandparents?

The average amount of DNA inherited from a great-great grandparent is 6.25%. This means that you might share about 6.25% of your DNA with any of your 16 great-great grandparents.

In centimorgans, this would be an average of about 466 cMs.

There is also a range of DNA that a person can expect to have inherited from a great-great grandparent, but since we don’t actually have many DNA comparisons between people and their great-great grandparents (for obvious reasons), there isn’t enough data to provide you with a specific number.

What we do know is that we can share very small amounts of DNA with our third cousins, and those cousins are descended from our great-great grandparents (our most recent common ancestor).

While it is possible to share no detectable DNA with a third cousin, it is likely that you both inherited different DNA segments from the great-great grandparent you share. Some people would take no shared DNA between two third cousins to mean that one of them inherited no DNA from the great-great grandparent, but this is unlikely to be the case.

How much DNA did you inherit from your great-great-great grandparents?

We will have inherited about 3.125% of our DNA from each of our 32 great-great-great grandparents. Again, we cannot actually compare our DNA with that of our 3rd great-grandparents, but we do know that there will be a range of shared DNA with ancestors at this level based on statistics, and how DNA is inherited.

It is at the 3rd great-grandparent (short for great-great-great grandparent) distance that we see it become theoretically possible that inherited no traceable DNA. There is about a .01% chance to have inherited no DNA from a 3rd great-grandparent.

Of course, we did inherit DNA from most, if not all, of our 3rd great-grandparents. The amount is small, however, and is about 233 centimorgans, the same amount that we might share with a second cousin.

How much DNA did you inherit from your great-great-great-great grandparents?

In theory, we might have inherited about 1.5% of our DNA from all 64 of our 4th great-grandparents, or our great-great-great-great grandparents. If all of our 4th great-grandparents were to take DNA tests to have their DNA compared with ours, we would probably see a range, with some sharing very tiny percentages with us, and others sharing slightly more than 1.5%.

At the 4th great-grandparent level, it is slightly more likely (about .56% probability) of having inherited no DNA from any of our 64 ancestors.

As we move further back in our tree, it becomes even more likely of having no traceable genetic relationship with a given ancestor. For example, there is a 37% chance of having no DNA relationship with a 7th great-grandparent, and only a 1.5% probability of having a DNA connection to a 14th great-grandparent.

Make no mistake. Even though there will be some ancestors from whom we will have inherited no DNA, or amounts too small to detect with our current technology, we will have inherited substantial amounts from many ancestors.

That’s where we got all of our DNA, after all.

Conclusion

I hope that this post has helped you understand how much DNA you might share with your more recent – and distant ancestors. If you have any questions about something that you read in this post, or if you would like to ask about a specific ancestor, please join us in the discussion below.

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