Why Use a Chromosome Browser

Diahan Southard

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A chromosome browser can help you understand how you are related to your DNA matches—and it’s a very cool visual!

Before we start, let me be very clear: 98% of the time, you do NOT need a chromosome browser to do successful genetic genetic genealogy work. Most of the time, it doesn’t matter how you are sharing DNA, only that you are sharing.

OK, now that I got that out of the way, let’s get down to using these things for a little insight, and a lot of cool science stuff.

Most of the major DNA testing companies have chromosome browsers. Though they may display the data a little differently, all of them show physical locations on each of 22 chromosomes where you and your genetic matches share DNA.

What do chromosome browsers look like?

Here’s what the results looks like on Family Tree DNA for a man whose DNA is being compared to three of his great-grandchildren. Where he overlaps genetically with each of them is shown in blue, red and teal, one color for each of the three great-grandchildren.

chromosome browser FTDNA.png

(The light grey are non-matching areas, and the gray and black striped sections represent areas that aren’t included in the testing analysis.)

Why use a chromosome browser

There are three reasons you might want to take a peek at a chromosome browser. First, pictures are more impactful than numbers. Second, you can get a better idea if you and your match share a recent common ancestor. And third, you can dig deeper into discovering a shared ancestor.

Put it in a Picture

To me, it’s mind-boggling that I can actually see a detailed physical breakdown of the DNA data I share with a relative. This is one of my favorite ways to use a chromosome browser: to see tangible evidence of my specific biological connection to a cousin—and to know that this exact piece of DNA was once walking around in one of our shared ancestors. (This is a fun way to get your relatives more engaged with their own DNA test results.)

Pieces vs bits (and the problem with glitter)

Another way to use a chromosome browser is to get a sense of how closely you may be related to your match. The total number of shared centimorgans only tells you how much TOTAL DNA you share. Those who are more closely related will share longer individual pieces of DNA, as opposed to the many, short bits shared by those who are much more distantly-related or who simply may share a lot of DNA because they come from endogamous communities.

You can think of these short bits like ancestral glitter. My husband HATES glitter. He has tried to ban it from the house, but when you have a little girl, glitter just comes on everything. Glitter is persistent, it lasts for months on sofas and carpets and, well, everywhere. You need to be sure the pieces of DNA you see showing up are evidence of a real—and recent—relationship, not just leftover glitter.

In general, you want shared pieces of DNA over 10 cM. Anything smaller is likely just glitter.

Dig Deeper

Some genealogists use chromosome browsers to identify groups of people who all share the same pieces of DNA (triangulated groups, or TGs). Let’s say you and a couple of known closer cousins (like first or second cousins) share the same piece of DNA. That often means you got that shared piece of DNA from your common ancestor or ancestral couple.

Now let’s say you add a mystery match to see if he or she also shares that same piece of DNA. IF they do share, you may conclude that this new match is related to that ancestral couple you know you share with your close cousins.

It’s a good thought and may sometimes work. But BE CAREFUL.

Using this technique with more distant matches, like third and fourth cousins, can be problematic. The more distant the shared ancestral relationship, the more unlikely that multiple cousins share the same piece of DNA. Shared DNA between multiple fourth cousins is less likely to point to a single recent ancestor and more likely the result of belonging to a shared population group (see that earlier link on endogamy). For example, perhaps you may all share Ashkenazi Jewish roots, and you’re looking at a very “Jewish” piece of shared DNA.

Chromosome browsers are available at 23andMe, Family Tree DNA, MyHeritage DNA, and are promised to be coming soon for LivingDNA customers. Here’s a more detailed article on the MyHeritage DNA chromosome browser, and some additional (but more complicated) ideas for using chromosome browsers to place matches on your genetic family tree.

Updated Winter 2022: More productive than chromosome browsers: Use your DNA matches (and their trees) to identify specific ancestors on your tree! I’ve set out a step-by-step methodology for doing this in my new quick reference guide, Finding Your Ancestor Using Your DNA.

What to read next: this excellent two-part series on pedigree collapse, which includes the math you need to see how this phenomenon may be affecting your genetic relationships.

This article contains affiliate links. If you click on an affiliate link and make a purchase, Your DNA Guide will receive a small payment, which does not affect the price you pay but which does help Your DNA Guide continue to bring you great articles like these!

<a href="https://www.yourdnaguide.com/author/guideyourdnaguide-com" target="_self">Diahan Southard</a>

Diahan Southard

As founder and CEO of Your DNA Guide, Diahan Southard has been teaching people how to find family history answers in their DNA for several years, and she's been in the genetic genealogy field since its infancy. Diahan teaches internationally, writes for popular magazines, consults with leading testing companies, is author of Your DNA Guide–The Book, and producer of Your DNA Guide–the Academy, an online learning experience.

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9 Comments

  1. Allokara

    Hello,
    Why do chromosomes browser only shows 22 chromosomes when we have 22 pairs of chromosomes ? For each pair of chromosomes, we have a chromosome which comes from our mother and one from our father. It means there is 44 different chromosomes. Why is it like that ?

    Reply
    • Diahan Southard

      Great question! We do have 23 pairs of chromosomes. That 23rd pair is an XY if you are a man, and an XX if you are a woman. 23andMe and MyHeritage do not report results for the X chromosome so in the chromosome browser you will only see 22 chromosomes. You do see the X chromosome in the browser at FTDNA.

      Reply
      • Allokara

        Thank you for the information but I was not talking about sexual chromosomes. I took MyHeritage DNA test and i don’t understand the chromosome browser because there is 44 autosomes in a human DNA but it shows only 22. Could you tell me why ?

        Reply
        • Diahan Southard

          Ah! I understand your question now. Yes, you do have two copies of each chromosome, but all the companies just represent those two on a single line. That’s because they can’t tell from testing which of the two copies of chromosome 18 you are matching on. So it is just shown as one line.

          Reply
          • Allokara

            Thank you. I understand now 😉

  2. Cheryl L McIntire

    Hello,
    You stated below in a response "Yes, you do have two copies of each chromosome, but all the companies just represent those two on a single line." This does not make sense to me when I compare my chromosomes in the browser to my Mother’s chromosomes, I would expect to see 50% gray (non matching) and 50% colored (matching) if that were the case, wouldn’t I? I see probably 95% colored matching of chromosomes between mine and my Mom’s. What am I missing?

    Reply
    • Diahan Southard

      Cheryl,
      If the chromosome browser showed BOTH chromosomes on TWO lines, you are right, you would see one entire grey chromosome (the one you got from your dad) and one colored (sharing) chromosome when you compare with your mom. But because you only see ONE line, when you look at your mom’s shared DNA the entire line is covered and we don’t actually see the other 50% of your DNA that is not shared with her. Does that make sense?

      Reply
  3. MLeo Cooper

    I share a 62 cM match with an apparent second cousin on chromosome 22, most of the length of that chromosome. Overall, it’s a 180 cM match. None of my other cousins that have an available chromosome browser displayed have an overlapping match on that particular chromosome. This person’s family tree is not helpful and he does not respond to messages. How does this help me?

    Reply
    • Diahan Southard

      You don’t really need a chromosome browser, just the 180 cM match. How much DNA are you cousins sharing (it doesn’t have to be on this chromosome)? Depending on which of your cousins are and aren’t sharing, you can narrow down which branch of your family this match shares with. Then use the shared cM project to help you estimate their relationship. http://www.yourDNAguide.com/scp.

      Reply

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