What’s a CentiMorgan, Anyway? How DNA Tests for Family History Measure Genetic Relationships

If you’re doing DNA tests for family history, you may see lots of predicted cousin matches: 2nd, 3rd, 4th, etc…..But what does that predicted genetic relationship actually mean? Learn about centimorgans, the powerful genetic genealogy unit of measure, and how it helps your research.

genetic relationships and centimorgans

How DNA Tests Measure Genetic Relationships

When we are looking at genetic relationships, there are also many ways we can measure them. But ultimately, we want the testing company to tell us how likely it is that a particular individual shares a single, recent common ancestor with us. One factor in this calculation is to take into account the total amount of DNA we share with that match.

Currently, all the testing companies are reporting this sum in centimorgans (cMs).  Every company reports to you the total number of shared cMs, as outlined below.

  • AncestryDNA: Click on the match to access the personal profile page for that match. In the second section, under Predicted Relationship, you will see the confidence level. To the right of the confidence level, you will see a grey circle with a little “i” in it. Clicking there will show you the total amount of shared cMs as well as how many pieces of DNA you share.
  • Family Tree DNA: On the main match page for your Family Finder results, you will see the total amount of shared cMs in the third column.
  • 23andMe: You can see the percentage of shared DNA from the main DNA Relatives home page. To convert the percentage into centimorgans, just multiply your percentage by 68 (that will at least get you close). You can also see total shared cMs in the chromosome browser tool (go to Tools > DNA Relatives > DNA).
  • MyHeritageDNA: The total amount of shared DNA is shown on the main match page under the title Match Quality. MyHeritage also has a new DNA Match Review page. Click here to read more about that.

Centimorgan: A Genetic “Crystal Ball”

It is very tempting to think of a cM just like you would think of an inch or a centimeter, and for all practical purposes, that is okay. But it is actually much more complicated than that.

A cM is actually more like a crystal ball: it helps us predict how likely a piece of DNA looks exactly as it did a generation ago. This, in turn, helps us calculate how far back we should be looking for the common ancestor between two people.

But for our practical purposes, you can use the total amount of shared DNA, in combination with this chart compiled by Blaine Bettinger and the Shared cM Project, to better assess your genealogical relationship with your match based on your genetics.

To use the chart, take the total amount of shared DNA you have with a match, and look up that number in the chart to get an idea of what kind of genealogical relationship might best fit the genetics that you see. For example, if I share 69 cM with my match, we might be third cousins. But we might also be second cousins once or twice removed.

How do you figure out which one? Simply put: do genealogy research! It’s time to use traditional records and research skills to better understand the genetic clues in your family history mysteries.

My series of DNA quick reference guides can help you get the most out of your DNA tests for family history. I definitely recommend the value-priced bundle of all 10 guides. But I especially recommend the guides listed below if you’re to the point where you’re trying to understand what genetic relationships mean:

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Land Ownership Maps: New Online Property Map Tools for U.S. Genealogy Research

Screenshot from First Landowners Project video, shown below.

Screenshot from First Landowners Project video, shown below.

Do you ever find it difficult locate U.S. property owned by your ancestors? Two online resources for land ownership maps are available by subscription at HistoryGeo.com, which might just prove helpful!

The First Landowners Project aims to map out the original landowners in public land states. Currently, they’ve charted about 8.8 million original landowners from 21 different states (Alabama, Arkansas, California, Colorado, Florida, Iowa, Illinois, Indiana, Kansas, Louisiana, Michigan, Minnesota, Mississippi, Missouri, Nebraska, Ohio, Oklahoma, Oregon, Texas, Utah, Wisconsin). “We will continue to add more of the Western states soon,” says a recent press release. “Information on eastern states can be found on our frequently asked questions blog entry.” Watch a video demonstration of this project below. Click here to read a detailed description of it.

The Antique Maps Project is a growing collection of historical maps that contain names of U.S. landowners. Their comment: “Many of these maps are indexed and searchable, and the ones that are not will be (thanks to our volunteer labeling program).” Watch a video about this project below:

Learn more about great mapping tools for genealogy by searching our blog by the Sanborn Fire Insurance Maps Premium PresentationMaps category (do this from our home page, lower left side). Or become a Genealogy Gems Premium member to gain a full year’s access to video classes like:

  • 5 Ways to Enhance Your Genealogy Research with Old Maps
  • Google Earth for Genealogy (use Google Earth to identify an old photo location)
  • Google Earth: Follow Your World
  • Time Travel with Google Earth
  • and NEW! Sanborn Fire Insurance Maps

 

Top 10 Genealogy Gems Blog Posts: Share and Enter to Win!

top 10 blog posts shareWe are celebrating our 1000th Genealogy Gems blog post with a list of our Top 10 Posts. Share this post on Facebook and you could win an inspiring family history writing video!

I can hardly believe it. This month, the Genealogy Gems website will reach a milestone 1000 blog posts! Thank YOU for your emails, phone calls and comments at conferences. I often share your success stories and use your feedback to bring you more great content.

Below is a list of our most-read posts so far. Did you miss any? Keep reading to learn how to win a a great family history writing prize by sharing this post on Facebook!

Our Top 10 Blog Posts

1. Ancestry Up for Sale? By far the most-read post in 2015! We weren’t just talking about the sale rumor, but sharing advice on saving your Ancestry trees, sources and DNA, which everyone should do.

2. Best Genealogy Software: Which You Should Choose and Why. This is my spiel on why you should keep your master family tree on software at home–not on your favorite genealogy website. It includes my top picks for family tree software, including free options.

3. Four Fabulous Ways to Use the Library of Congress for Genealogy. A lot of you are interested in the Library of Congress’ online resources for digitized photos, newspapers and how-tos for archiving your family history. Read all about it!

4. Free Google Earth for Genealogy Class. The conference lectures I give on Google Earth for genealogy are so popular that I created a free video that everyone can watch from home. Click on the post, and you can watch the video, too.

5. AncestryDNA Review and Breaking News: Updates Launched. Our own DNA correspondent Diahan Southard penned this popular post on AncestryDNA’s ground-breaking integration of our genetics data and our genealogy trees.

6. Seven Free Google Searches Every Genealogist Should Use. Are you getting the most out of free Google search technologies? Scan this list and see what’s missing from your search strategies!

7. NEW! Try This Now! U.S. Social Security Applications and Claims Index. For U.S. researchers, this was the blockbuster database of summer 2015. Millions of parents’ names, birthplaces and more now beef up this go-to Social Security database–its’ far better than its sparse predecessor, the SSDI.

8. Confused by Your AncestryDNA Matches? Read This Post. Another hit from DNA expert Diahan Southard! A great explanation of how to use your New Ancestor Discoveries on AncestryDNA.

9. How are We Related? Use a Cousin Calculator. It’s a simple, easy online tool, shared in response to a listener’s question.

10. New AncestryDNA Common Matches Tool: Love it! Diahan reports on a fabulous online tool that pulls out shared genetic matches between two people at AncestryDNA.

win this prizeWill you please share this post on your Facebook timeline to help me spread the word about the “gems” you can find on the Genealogy Gems blog?

Here’s a little extra incentive: Use the hashtag #genealogygems and SHARE THIS POST ON YOUR FACEBOOK PAGE BY FRIDAY (November 20, 2015), and you’ll be entered in a contest to win the Pain Free Family History Writing Project video course download. It’s presented by Gems Contributing Editor Sunny Morton and donated by our friends at Family Tree University. Of course you’re welcome to add any comments on your “shared” post, like which Genealogy Gems blog post has most inspired you or helped your research. That feedback helps us bring you more posts you’ll love.

media_icon_like_400_wht_9163Ready, set, SHARE! And thank YOU for helping me celebrate our 1000th blog post here at Genealogy Gems.

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