What is a Chromosome Browser?
Over a decade ago now when I first started researching my family tree I was armed with a sparse amount of family history information and the ability to research documents through Ancestry. It was slow going and I made plenty of mistakes.
Quickly however I became aware of Ancestry’s DNA testing and saw it as a possible game changer for my research given that I knew so little about either side of my family at that time. In school I was good at biology so I knew some of the basics of DNA scientifically speaking but the world of genealogical DNA opened up things I had no idea about.
One of these things was chromosome browsers. I already knew that we all have 22 pairs of chromosomes and one pair of sex chromosomes which vary depending on biological gender. So in total we have 23 chromosomes with male sex chromosomes being XY and females being XX.
Now understanding chromosomes and DNA inheritance isn’t exactly entry level science but nor is it that complicated really. In this post we will try and show you how easy using a chromosome browser is and just how much it can teach us about our family tree.
What Is a Chromosome Browser?
You may have seen chromosome browsers on various genealogy websites that allow you to upload your DNA test results. Essentially these browsers allow you to compare your DNA with that of someone who shares a significant amount of genetic material in common with you.
The key point of a chromosome browser is that it allows us to see the location of the DNA we share with someone in comparison to our respective chromosomes. We are mainly talking about the 22 pairs of chromosomes which are not sex specific.
We receive 23 chromosomes from each of our parents and they match up to make the 23 pairs of our complete DNA. The 23rd set as mentioned are the sex chromosomes X and Y which have their own unique gender specific inheritance patterns.
As an example let's look at the DNA I share with my second cousin once removed. We share 133 centimorgans of DNA of which 50.4 centimorgans are in a single strand on my 11th chromosome.
In the picture below you will see the table with the first column being the chromosome number with the next two showing the start and stop points of the segment on the DNA strand. The final table is labeled SNP’s and this stands for single nucleotide polymorphisms. This number indicates now many of these SNPs were tested to get this result.
It is important to note that close relatives will share multiple segments of DNA and often in very very long sections. Those who are more distantly related will share shorter sections and fewer. This information is important to help us understand the benefits of these chromosome browsers.
Where Can You Find Chromosome Browsers?
Increasingly more and more of the DNA companies are expanding their DNA tools in an effort to make their results more useful to their customers. The days of ethnicity report and a simple result of how many centimorgans you share with a match are in the past.
Today we have varied and interesting tools at our disposal and with some companies this includes chromosome browsers. Those companies currently offering a chromosome browser to allow you to compare your DNA to a specific match include:
- Family Tree DNA
- My Heritage DNA
Ancestry does have a DNA painter tool but this is at present specifically attached to their Ethnicity Inheritance tool. This specially shows the ethnicity regions inherited from our respective parents and on which chromosomes those markers are found.
You may not compare your DNA through the Ancestry chromosome painter with any of your matches. It only pertains to your inherited ethnicity markers and on which chromosomes they can be found. This does not mean you should avoid Ancestry for your testing as you can upload your raw DNA from Ancestry to sites that do have chromosome browsers.
There are several sites that do not require you to have a DNA test with them but you can upload your raw data from another company to compare against their databases. These sites include
- Family Tree DNA
- My Heritage DNA
GEDmatch is a great website that does not require you to buy a DNA test from them as they do not sell them. They have many tools you can use including a chromosome browser and you can potentially find matches who tested at completely different companies than you did.
How Do Chromosome Browsers Help?
So you have performed a one to one DNA match chromosome browser comparison and you can see a visual representation of the segments of DNA you share. What exactly does this mean and how does it actually help you?
Well in truth in one to one this really doesn’t tell you much except that you and your match inherited these segments of DNA from common ancestors. We already know that though because you have a significant DNA match.
The real benefit comes when you add other matches to the mix. So let's assume for example you and a cousin match share a sizable segment of DNA on the third chromosome. You compare a different match and they share DNA with both of you on the third chromosome either within or overlapping the same position.
This result indicates that all three of you share the same common ancestor which if you can determine the identity for two of you then you can confirm it for the third match.
It should be noted that DNA segments are passed down through a process known as recombination. The segments of DNA recombine with each of your parents giving you a mix of DNA from their own parents. This recombination however stays on the same chromosome so if your father has the DNA on his 5th chromosome and passes it to you then it remains on the fifth chromosome in you.
So you won't have DNA from a parent's 8th chromosome being passed down to your 12th chromosome. This remains the same generation after generation so even if you have a mutual great-great-great grandparent with a DNA match your common DNA will be on the same numbered chromosome.
What does this ultimately mean? Well all of your matches that share DNA in roughly the same location on a specific chromosome likely share the same common ancestor with you. The question is sometimes who was that ancestor? Well hopefully by determining the cousins who also descend from that ancestor you may find out who that ancestor may have been.
Now having explained how the browser essentially works it is time to throw a potential spanner in the works. As earlier mentioned we get two sets of these 22 chromosomes one from our mother the other from our fathers.
This means we need to be sure that we match these people on the same chromosome. If however you are matching two people on say the 6th chromosome but one is inherited from your mother and the other your father then they are likely not themselves related to each other.
Beware of False Positives
Now many of us likely have thousands of matches but there does reach a point where a DNA match is so low that it may not be correct. As mentioned DNA is inherited through random recombination this is why we may share multiple DNA segments with someone over several chromosomes.
Sometimes we may share only a few centimorgans of DNA with a match perhaps 5 or so. Now in the grand scheme of the DNA molecule this could mean we have a distant common ancestor or it could mean we are not related at all.
When centimorgan levels are low the match can actually be the result of coincidence rather than inheritance. A segment of DNA just happens to match someone else but you do not share a recent common ancestor.
It is always best then to focus on closer matches with higher centimorgan levels in common. These are the ones which are more likely to be confirmed as they would pertain to a more recent common ancestor.
Chromosome browsers are very handy tools that let you compare the location and sizes of DNA segments you share with a cousin match. They may seem visually daunting but with concentration and a little knowledge you can master them.
The basic concept is that a match will show shared DNA in roughly the same place on the same numbered chromosome. Other matches with the same common ancestors may also show DNA in roughly the same locations or perhaps on different chromosomes.
We can inherit different segments of DNA from a common ancestor but still be related to two different cousin matches. They may have gotten one segment of DNA from our mutual ancestor while the other person got different DNA. For our part we got both segments from that ancestor so match both people though they themselves do not match.
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" What is a Chromosome Browser?". NameCensus.com. Accessed on October 2, 2023. https://namecensus.com/blog/what-is-a-chromosome-browser/.
" What is a Chromosome Browser?". NameCensus.com, https://namecensus.com/blog/what-is-a-chromosome-browser/. Accessed 2 October, 2023
What is a Chromosome Browser?. NameCensus.com. Retrieved from https://namecensus.com/blog/what-is-a-chromosome-browser/.