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:

Thanks for sharing this post with someone who would enjoy reading it! You’re a gem!

Disclosure: This article contains affiliate links and Genealogy Gems will be compensated if you make a purchase after clicking on these links (at no additional cost to you). Thank you for supporting Genealogy Gems!

How to Upgrade Your DNA Test with Your DNA Guide

When it comes to chocolate my general rule of thumb is that more is usually better! The same is true with DNA testing. With this big DNA test upgrade sale, now is the perfect time to get MORE! I love being Your DNA Guide here at Genealogy Gems, and today I’ll walk you through how to get the best deal and the right tests. Take my hand, and let’s get upgrading!

more is better with dna

Diahan SouthardThis month, Family Tree DNA is running this Family Tree DNA’s Friends & Family sale, which means that all of the kits and upgrades are on sale! This sale is the perfect time to upgrade your DNA tests. (By clicking our link above you are supporting the free Genealogy Gems Podcast. It doesn’t cost you anything extra, and we will receive compensation from the affiliate link. Thank you!)

Once in your account, click the Upgrade button. In very basic terms, to Upgrade means that they are going to go back to your DNA sample that they have on file, and do more testing.

upgrade your DNA test

Depending on the tests you have already had completed at Family Tree DNA, you will see several different options in the Upgrade menu. Most of you will see this box, listing the option to do more advanced testing, find gene variants, or order certificates.

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If you’re testing for general genealogy purposes, you can most likely ignore all of those options. The advanced testing is aptly named as it is only for very specific, very, advanced problems. The gene variant report can be interesting, but you can get a similar report for only $5 from Promethease.com. As for the certificates, that is up to you. It is a printed report of your DNA values for either your YDNA or your mtDNA test. These are nice to give to relatives that have tested for you that might want something tangible to hold as evidence of their participation in your genetic genealogy efforts.

The last option in this box is to have a personalized report written. This will be several pages of information about the DNA testing you have had completed, but don’t expect them to find your ancestors or do much interpretation of the results.

Beyond those options, if you have not had mitochondrial DNA testing completed, or if you have only had the lower mtDNAPlus test completed, you will see options to evaluate your mtDNA. If you are going to try to do family history with your mtDNA test, you need to have the Full Sequence test completed. For the most part, using mtDNA in your family history won’t get you very far, but it is a good record of your direct maternal line.

ftdna tests

If you are a man with the YDNA test, you will also see options to upgrade your YDNA test to a higher number of markers. You will want to upgrade from 37 to 67 or 111 if you have other matches on your match page who have also tested at those higher levels and you would like to get a better comparison. You can check to see if they have tested at a higher level by looking at your match page under their name. In general, the 67 marker test will help you better decide if you are or are not related to someone, while the 111 marker test will help you better determine how you are related to known connections on your match list.

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If you have not yet taken the Family Finder test at Family Tree DNA, that option will present itself as well. If the person tested is still available for testing, you should actually start their autosomal DNA testing experience with AncestryDNA, then transfer for free into their FTDNA account. If your family member is deceased, then you can get permission from their closest living relative, or whoever is administrating their account, to have them tested on the Family Finder test at Family Tree DNA.

So remember my general rule of thumb when it comes to chocolate and DNA testing, more is usually better. Click here to shop the Family Tree DNA Friends & Family!

Get more help with my quick guide: Understanding Family Tree DNA.

AncestryDNA Opt-Out Options for DNA Matches: What This Means for You

A new AncestryDNA opt-out option allows DNA test takers to not participate in DNA match lists: they do not receive matches or show up in others’ match lists. Your DNA Guide Diahan Southard weighs on in the implications for genealogy researchers who may worry about cousin matches they may miss.

AncestryDNA opt-out

New AncestryDNA Opt-Out Policy

Ancestry.com recently announced an update to their privacy policy. Current and future AncestryDNA users now have the option to opt out of the DNA matching feature.

When you take a DNA test, you receive two different kinds of results from the DNA sample that you submit to your testing company:

  • information about your ancestral origins and
  • a list of your DNA cousins.

Opting out of matching essentially cuts the value of this product in half. You only get the ancestral origin information, and you forfeit access to your list of genetic matches. Opting out doesn’t just mean you can’t see them: it means that they can’t see you either.

AncestryDNA joins 23andMe in providing this option to their clients. You can look at this move as Ancestry’s response to an ever-expanding global audience, many of whom are not genealogists or are reluctant to have their DNA compared to others for a variety of reasons. It is important for them as a company to provide options for their clients to experience their product in a way that works best for them.

What the AncestryDNA Opt-Out Policy May Mean for You

What does this new opt-out option mean for genealogists? Hopefully, not much will change. Ancestry reports that overwhelmingly, people are opting in.

There has been quite a bit of push-back to this announcement, especially from the adoption community. DNA testing has been a tremendous source of information for those seeking out their biological relatives, and many fear that this change will limit access to quality DNA matches. But we will all still be able to do good genetic genealogy work, even as we are each allowed to choose whether to participate in the matching feature. To understand this better, it is important to see this issue from the other side, from the side of a person who might want to opt out. Here are two possible scenarios:

Scenario #1: Susan would really like to explore her heritage. She hasn’t tested before because she didn’t want to see cousin matches for a variety of personal reasons. But now she does test and opts-out. The community hasn’t lost anything because Susan would never have tested in the first place. But after exploring her ethnicity results and noticing membership in a couple of Genetic Communities, she begins to wonder more about her ancestors and decides to opt-in to matching, after all. In this scenario, the Opt-Out policy offers users a way to comfortably give DNA testing a try.

Scenario #2: Ryan heard about AncestryDNA while watching TV last year and ordered a kit. But then last week he heard about the ability to opt out, and went in and changed his account settings. So one day you could see Ryan on your match list, and the next you didn’t. We as a community would certainly see that as a loss. However, consider the circumstances that might have caused Ryan to hit that opt-out button. Perhaps Ryan had no idea how to use the match list, no interest in using it, and found it a bother to get correspondence from people. Perhaps Ryan found something unexpected, like that he wasn’t his father’s child, and he needed some time to deal with it. Maybe Ryan is under pressure from his sister, who didn’t want him to test in the first place (perhaps she knows something he doesn’t about their family tree, or she’s afraid of how any results and revelations might impact her). The short of it is: It doesn’t matter why Ryan opted out, it is his personal right to do so. Just as an adoptee has the right to seek out their heritage, others have the right to keep their family secrets to themselves. This scenario does support the idea that you should review your DNA matches frequently and record information about them in your own master match list, which I talk about in my quick reference guides, Organizing Your DNA Matches and Breaking Down Brick Walls with DNABy promptly recording matching results, you will have them to work with even if the tester decides later on down the road to opt out.

As a genealogy community, we can educate others about the value of the match list, while at the same time cautioning them that unexpected connections may appear. So in everyday conversations, share your own experiences—whatever these may be. Maybe it was affirming for you to see that the dad you grew up knowing is indeed your biological father. Perhaps you can share a story about the power of using a list of fourth cousins to discover information about your third-great-grandfather. Maybe you’ve discovered a new connection—and maybe that connection isn’t yet comfortable or fully explained, but you’re glad to know about it.

Learn More about AncestryDNA Testing

Get the most out of your AncestryDNA testing experience with my quick reference guides! I recommend:

  • A Guide to AncestryDNA How to find your best DNA matches, interpret ethnicity results, link your tree, understand relationship ranges and DNA Circles, and work with Shaky Leaf hints. 
  • Autosomal DNA for the Genealogist. What autosomal test can tell you, who can be tested, how to interpret your ethnicity results, and more.
  • Organizing Your DNA Matches. How to keep track of your matches and apply what you learn from them to your family history.
  • Breaking Down Brick Walls with DNA. What to do next to maximize the power of DNA testing in genealogy. Take your DNA testing experience to the next level and make new discoveries about your ancestors and heritage!

Disclosure: This article contains affiliate links and Genealogy Gems will be compensated if you make a purchase after clicking on these links (at no additional cost to you). Thank you for supporting Genealogy Gems!

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