4
Dec

How Much DNA Do I Share With My Grandchild?

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Are you wondering how much DNA you would share with a grandchild?  Is it a set amount, or could it vary?  What’s the percentage of DNA that we share with our grandchildren?  Do grandchildren always show up on DNA tests?  How much of our ethnicity might they share with us?  I’ll answer all of these questions – and more – in this post.

With the growing popularity of DNA tests like Ancestry DNA and 23andMe, the chance that we will have several generations of DNA matches on our list grows.  Ancestry DNA now has more than 14 million users, and when you combine that with the users of the other DNA testing sites, this means a lot of DNA matches for all of us.    Many of us will eventually have children, nieces and nephews, great-grandchildren, uncles, aunts, and parents – and many more relatives too numerous to mention – on our DNA match list.

Now, let’s talk about grandchildren DNA matches, shall we?

How much DNA do you share with your grandchild?

A grandchild, whether a granddaughter or a grandson, will generally share between 1300-2300 centimorgans with either of their grandparents.  Expressed as a percentage, grandparents will between 18-32% of their DNA with the offspring of their children, with the average being about 25%.

How much DNA do I share with my grandchild on Ancestry

As you can see, my grandmother shares 1855 cMs with me. This is right in the middle of the “average” range of shared DNA between grandparent and grandchild. This screenshot is from our Ancestry DNA results.

INSERT HOW MUCH DNA DO I SHARE WITH MY GRANDCHILD ON ANCESTRY HERE

Why is there a range of shared DNA between grandparents and grandchildren?  Does it seem odd that if a parent and child share a fairly exact 50% that there could be such a range of shared DNA seen between grandparents and grandchildren?  The reason behind this is because when your child passed down his or her DNA to your grandchild, 50% of their DNA was randomly selected to give to the grandchild.  Since your child shares an equal amount of DNA with both you and their other parent, some DNA from each of you (the grandparents) was passed down to the next generation.

So, a grandchild doesn’t share the same amount of DNA with all of their grandparents?

As you might have guessed, since a child inherits 50% of their parent’s DNA and the DNA is randomly selected, sometimes the grandchild shares slightly more DNA with one grandparent than the other.  It will always fall around the range that I mentioned above, however.

As you can see in the image below, my daughter doesn’t share the same amount of DNA with my mother as she does with my father.  She shares 26% of her DNA with my mother (her grandmother), and 24% of her DNA with my father (her grandfather).  I got this cool graphic and helpful information from my daughter’s Gene Heritage Grandchild Report.  My parents enjoyed finding out which grandparent shares more DNA with her, and of course, my mom teased my dad a little bit 🙂

How much DNA do we share with our grandchildren

This is part of the Grandchild Report, offered by Gene Heritage. This is only a small portion of information provided in the report (other info includes how various traits were passed down over the three generations)

Will a grandchild always show up on a DNA test?

Our grandchildren will always show up on DNA tests.  Since our grandchildren are directly descended from our children, there is no way that a grandchild would not match us genetically.  Barring an error in testing (exceptionally rare), it is statistically and scientifically impossible for a grandchild not to match a grandparent.

The exact category that a grandchild gets placed in on a DNA match list will depend on the company that you test with.  Most people will find that their grandchildren show up in the “Close Family” group on Ancestry (though there is a chance that high sharing grandparents/grandchildren will show up in the immediate family category, and low sharing might show up in the first cousin category).  DNA testing companies make a guess at the estimated relationship with our DNA matches, and it is up to us to figure out the exact relationship.

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How much of a grandparent’s ethnicity regions will a grandchild share?

Even though the average amount of DNA passed down from a grandparent to a grandchild averages about 25%, there are a few reasons that the ethnicity regions that show up in our grandchild’s ethnicity estimate might not seem “right” compared to our own estimates.

  • As you know, the amount of DNA shared between grandparents and grandchildren can range from about 18-32%.  This means that a grandchild might inherit more of one grandparent’s ethnicity regions, leaving behind some of those that belonged to the other grandparent
  • Because the 18-32% of the DNA that a grandchild inherits from a grandparent was randomly selected from the 50% of the randomly selected DNA that the child of the grandparent inherited, it’s possible for entire ethnicities to not get passed down from grandparent to grandchild.

Imagine a scenario where a grandparent is 35% Irish and 65% French.  This grandparent has a child and passes down 50% of their DNA to their offspring.  It’s randomly selected DNA, but since the grandparent has more French than Irish, there is a good chance that the child will get a good deal more French than Irish.  It’s possible for the child to get almost no Irish than French, and it’s also possible to pass down all of the Irish and only 15% French (though less probable).

To move our scenario along, let’s say that the child of the grandparent inherited 20% Irish and 30% French.  The other parent of the child was 50% Native American, so now we know that ONE of the parents of the grandchild is 50% Native American, 20% Irish, and 30% French.  When the parent has a child, they will pass down a randomly chosen selection of DNA to their child (the grandchild).  It would be possible for them to have any sort of combinations of ethnicity regions.  From the grandparent, they might get no Irish, 30% Native American and 20% French, or 16% Irish, 16% French, and 18% Native American, to name a few of the endless possibilities.

So while we do know for sure that a grandchild will share DNA with their grandparents and that they will have inherited some of their ethnicity regions, there is no way to guarantee a way in which ethnicity is passed down to a grandchild.

Note:  This is the reason that some ethnicity regions seem to “disappear” after a few generations.  If a grand parent has an ethnicity region on their estimate but they only have a small percentage (say, 2% of that region), it’s unlikely (yet not impossible) that this region would get passed down to the grandchild.

How to find out how much DNA you share with your grandchild?

If you haven’t yet done a DNA test and are interested in finding out how much DNA you share with your grandchild and other relatives, why not check out my post, “The Beginner’s Guide to DNA Testing: the Ultimate Strategy” to learn which DNA test is best for you and your family’s interests.

Conclusion

I hope that this post helped you understand how much DNA you share with your grandchild, how to find out how much DNA you share with your grandchild, and why a grandchild would always show up as a match for you on a DNA test.  If you have any questions about something that you read here, or would like to share your experience with a grandchild DNA match, I would love to hear from you in the comments.

Thanks for being here today.

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How Much DNA Do I Share With My Grandchild?
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Are you wondering how much DNA you would share with a grandchild? Is it a set amount, or could it vary? What's the percentage of DNA that we share with our grandchildren? Do grandchildren always show up on DNA tests? How much of our ethnicity might they share with us? I'll answer all of these questions - and more - in this post.
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Who Are You Made Of
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