How Much DNA Do You Share With a Grandparent?

Do you want to know how much DNA you share with your grandparents? In this post, learn all about shared DNA between you and your four grandparents.

You will discover:

• Whether you share DNA with your grandparents
• The percentage of DNA and number of centimorgans shared with a grandparent
• How many segments of DNA you should share with your grandmother or grandfather
• Examples of shared DNA between real people and their grandparents
• What you can learn from your grandparent’s DNA results

The growth in popularity of DNA testing has led to millions of people getting tested and wondering how much DNA their relatives should share with them. Grandchildren and grandparents are no exception.

If one or more of your grandparents have done a DNA test, this is actually a really amazing gift to you. Through their results you will be able to learn much more about your family’s ancestry than you could with just your own results.

I will explain why towards the end of this post. You don’t want to skip that part!

Let’s get started learning how much DNA you share with your grandparents, and the nature of that shared DNA.

Does your DNA match with your grandparents?

Yes, your DNA will always match your grandparents on an autosomal DNA test like the one offered by Ancestry or 23andMe. This means that your grandparent, or grandparents, will be DNA matches to you.

It is impossible to not share DNA with your grandparents, as they are very recent ancestors to you. Because you are so recently descended from your grandparents, you share a substantial percentage of your DNA with them.

What percentage of your DNA comes from your grandparents?

On average, you inherited about 25% of your DNA from each of your grandparents. This 25% average shared DNA between a person and their grandparents is due to the way that DNA is inherited.

We each inherit 50% of our mother and father’s DNA. Since your mother and father inherited 50% of their DNA from each of their parents (i.e. your grandparents), it is easy to understand how you probably share about 25% of your DNA with each grandparent.

Plus, since our DNA had to come from somewhere, and we have four grandparents, it makes sense that about 1/4 of it would have come from each one. As I mentioned above, this 25% number is only an average, however.

The exact percentage of DNA that you might share with any of your four grandparents will be between about 18-33%. This means that if you are able to compare your DNA with that of any of your four grandparents, you might see shared DNA percentages anywhere between about 18-33%.

In fact, it is theoretically possible for the shared DNA percentage with grandparents to be a percentage or two under or over this range. Most people will see shared DNA with their grandmother or grandfather fall somewhere near the middle of that range, which explains the “average” of 25%.

The reason that there is a range of shared DNA with grandparents has nothing to do with which grandparent you look most like, or have the most in common with, or even whether you are male or female. Instead, the random nature of how DNA is inherited explains why we share such a variable amount of DNA with our relatives, even close relatives such as grandparents.

It is true that both your mother and father inherited 50% of their DNA from their parents, your grandparents. However, the 50% of the DNA that they inherited from their parents was selected through a process called “recombination.

In the case of DNA inheritance, recombination essentially creates a new, 100% unique copy of each chromosome using bits of the two copies of that chromosome. Only 50% of the total DNA on that chromosome can be passed down, which means that 50% is not passed down.

Each of your grandparents has two copies of their 22 numbered chromosomes, also called autosomes. Your parent inherited one copy of each numbered chromosomes from each of their parent to equal two total copies of each numbered chromosome.

The process again repeated with you, which is why you can only share about 25% of your DNA with any of your grandparents. This also explains why it is unlikely that you will share much less than 18% or much more than 33% of your total genome with your paternal or maternal grandparents.

How many centimorgans do you share with a grandparent?

As an average, we expect about 900 cMs to be shared between grandparents or grandchildren. The range of shared DNA with grandparents is about 1300-2300 centimorgans (cMs), whether it be your grandmother or grandfather.

There is a statistically small possibility that you could share slightly under 1300 cMs or a little more than 2300 cMs with a grandparent. This means that a person who falls slightly out of the range of what we typically see could still be your grandparent, especially if all other evidence points in this direction.

How many DNA segments do you share with a grandparent?

The number of shared DNA segments between a grandchild and their grandparent is not important in evaluating the relationship. The most important number is the total percentage or centimorgans of shared DNA, since we know that grandchildren always share substantial DNA with their grandparents.

However, many people are curious about the number of DNA segments shared between relatives. This is probably because there is so much variation, and it is all due to the process of recombination that I described in the first part of this post.

For the purpose of this post, I evaluated shared DNA segments between several sets of grandchildren and grandparents, with combinations of male/females, and found that the number ranged between 19-29 shared DNA segments. The mode (the number of segments that appeared most frequently) was 25 shared segments.

The size of the longest DNA segment shared between DNA matches can sometimes help in evaluating how two people are related. For this reason, I will share the that the range of the size of the longest DNA segments between grandchildren and their grandparents in my very small study was between 145-220 cMs.

Example of shared DNA between a person and their grandparent

Below, find an example of DNA shared between an individual and a grandparent, as seen on our AncestryDNA match list. In this case, the individual is me and the grandparent is my paternal grandmother:

As note, I inherited 27% of my DNA from my grandmother, who is my father’s mother. This works out to about 1855 cMs across 25 DNA segments.

I would not be concerned if I shared significantly less DNA with my grandmother, since I know that it is completely normal to share less than 1000 cMs or even more than 2000 cMs with a grandparent.

One conclusion that I can come to, however, is that I must have shared about 23% of my DNA with my paternal grandfather. This is because 50% of my DNA must have come from either of my two paternal grandparents.

The same is true for my maternal grandparents, since I know that the DNA that I inherited from both of them must equal 50%.

What can you learn from your grandparent’s DNA results?

DNA results from grandparents can help you learn a lot about where your ancestors likely lived in the past few hundred years, as well as your family tree. You are likely to find ethnicity regions in your grandparent’s ethnicity estimate that don’t show up as prominently in your results.

In fact, it is possible for your grandparent to have a region match their DNA that doesn’t show up in your results at all. This is because some of the DNA that they have that didn’t get passed down to you may match additional regions, which is a great reason to have grandparents test, if at all possible.

In addition, your grandparents are likely to have many DNA matches that do not show up on your DNA match list. The explanation is similar to the ethnicity estimate differences: your grandparents have DNA that matches other relatives that you did not inherit.

Furthermore, your grandparents will share significantly more DNA with DNA matches than you will, which can provide additional data points to evaluate to help determine how you and your DNA matches might be related.

All of this information will certainly be a great help in building your family tree and exploring your family’s unique history.

Conclusion

I hope that this post helped you learn everything that you wanted to know about the percentage and centimorgans of DNA shared between a grandchild and their grandparents, and everything related to this very interesting topic.

If you have any questions about something that you read in this post, or if you would like to share how much DNA you share with your grandparents, I would love to hear from you in the discussion below.

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