17
Dec

Need a DNA Centimorgan Chart?

Are you looking for a DNA centimorgan chart? In this post, you’ll find the best one out there so far. I’ll explain how to use and understand the chart, too!

Without access to a chart that helps us estimate our relationship to our DNA matches based on shared DNA, we would have a difficult time making sense of our DNA match list. A chart is a crucial part of understand our DNA matches.

The best DNA Centimorgan relationship chart

The best DNA centimorgan chart available to us is show below. It was developed by Blaine Bettinger (find his blog here), with input about more than 25,000 relationships.

In other words, it is a chart based on very comprehensive data, and is extremely useful to anyone who wants to know how they might be related to their DNA match.

Blaine Bettinger Shared DNA Chart
The data for this chart was painstakingly collected and compiled by Blaine Bettinger, and was generously shared with the CC by 4.0 Attribution license. You can find Blaine’s blog post about this chart here: Shared cM Project 2017 Update

This centimorgan chart can help us with Ancestry DNA matches, as well as matches from any other DNA testing company that provides the amount of centimorgans we share with our DNA matches.

How to understand the DNA centimorgan chart

When you have a DNA match you are trying to research, the first thing that you should do is find out how much DNA you share, expressed in centimorgans. For this process, you might want to know that centimorgans are abbreviated using the letters “cM”.

Once you know how many centimorgans you share with your match, you can then examine the chart to find all of the relationship possibilities for that amount of shared DNA. There is almost always more than one relationship possibility for any given amount of shared DNA.

Sometimes, there are many!

As an example, let’s take a a match that shares 217 cMs with you. We can look at the chart below, where I’ve circled in red each relationship that has a range of shared DNA that includes 217 cMs, that there are technically 19 possibilities:

Relationships that are possible at 217 cms
I circled in red the relationship possibilities for a DNA match that shares 217 cM with you This image was made by Blaine Bettinger and was generously shared with the CC by 4.0 Attribution license.

Use logic and information and yourself and your match to eliminate possibilities

Nineteen relationship possibilities! That’s way too many! There is an easy way to exclude some of these, so don’t worry.

Use genealogical data to decide on a few, or several possibilities

If you have access to your DNA match’s family tree or have contacted them and know some of the surnames in their pedigree, you can use this information to help determine which lines of the family they might be on.

Exclude some possibilities using age

For example, you’ll notice that two of the relationships would be elders in your family. If you know that your DNA match is younger than you, then you could cross the following relationships off your list:

  • Great-great aunt or uncle
  • Half-great-great aunt or uncle
  • Half-great aunt or uncle

If you know for sure that you don’t have any full siblings, you could exclude great-great niece or nephew from the list. This still leaves us with fifteen possibilities, but still don’t start worrying!

Exclude other possibilities using data points from your close relatives

If your sibling, parent, aunt, uncle, or cousin has tested, see if you can find out how much DNA they share with the match you are researching. If you can, you can use this data to further exclude a relationship possibility.

Using our example, if we know that your father shares 625 cMs with the match, we can eliminate many of the fifteen relationship possibilities. The only thing that you must keep in mind is that your match will have a slightly different relationship to your relative than they do to you (unless your relative is your sibling).

If we exclude the too-young and the too-old matches, just for the sake of moving things along, we see that we are most likely looking at just a few relationship possibilities! This is significantly better than 19!

Use shared matches to narrow possibilities down even further

So, how do we decide between the three-ish options we have left? Fortunately, we still have some tools at our disposal.

One things that you could do is see examine the matches that you are in common with your DNA match. By finding close relationships that also match your DNA match, you can exclude them from being descended from some of your ancestors.

By knowing which ancestors your match is or isn’t descended from, you can narrow things down considerably.

If you notice that your father shares DNA matches that you know to be from both sides of his family, like first or second cousins related to either of your grandparents, you can exclude half-first cousin. If your match is related to both sides of your father’s family, then you can be sure that they are descended from both of your father’s grandparents.

Is the DNA centimorgan chart 100% accurate?

The chart that I included in this post is, by far, the most helpful chart that is available to the public at this point in time. Even so, there are some important details that everyone should understand about the data collected and included for development of the chart.

The data for the chart was self-reported

The data used for collection of the chart was collected from tens of thousands of people who entered their relationship and shared DNA amounts into data collection form.

It’s important to understand that there are many ways in which the data reported might not be 100% accurate. Blaine Bettinger, the blogger and DNA expert who created the chart, excluded extreme outliers in order to prevent incorrect data from skewing the results, of course.

This means that the chart is best used in conjunction with good genealogy research and other DNA analysis.

Endogamy causes multiple relationships and can skew shared DNA

Some of us are related to our DNA matches in more than one way. Sometimes, it isn’t even possible to know this or know how many ways we are related to the same person.

For example, we might have a 5th cousin who shares 4th great-grandparents with us. This same cousin might also be a third cousin twice-removed on a different line of the family, and could even be related to us in a completely different way on a third line of our family tree.

This occurs most often in people who are descended from a common population. The result of this is that distant cousins might share multiple DNA segments with each other inherited from all of the common ancestors on different lines.

This can make the expected range of shared DNA for distant cousins higher than it really should be. There isn’t anything to be done, really, about this, but it’s good to know when viewing the chart.

Conclusion

I hope that you enjoyed finding this DNA chart to help you understand your relationship to your matches, and that you understand how to use it. If you have any questions about something that you read in this post, or if you would like to share your own experience using the chart, I would love to hear from you in the post below.

Thanks for stopping by today!

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