You get a notification that you have a new DNA match. The message says you share 42 centimorgans of DNA with a stranger, spread across a couple of chromosomes, and you have absolutely no idea how you are related.
That number and that stretch of chromosome are not random. They are a clue, and a fairly precise one. Chromosome mapping is the process of tracking exactly which ancestor gave you which piece of your DNA, segment by segment, until your chromosomes start to look less like a mystery and more like a labeled map of your family tree.
DNA Painter is the tool most genetic genealogists use to do this visually. Instead of staring at spreadsheets full of start and stop positions, you get an actual picture of your chromosomes with colored blocks representing each ancestor's contribution. This guide will walk you through setting it up and painting your first match, using a shared segment pulled from FamilyTreeDNA as the working example.
What Chromosome Mapping Actually Means
Every chromosome you have is a mix of DNA from your parents, who got their DNA from their parents, and so on back through your family tree.
A DNA match happens when you and another person share an identical stretch of DNA on the same chromosome, in the same position. That shared stretch, called a segment, was inherited from a common ancestor you both descend from.
If you know how a specific match is related to you, you also know which ancestor that segment came from. Chromosome mapping is simply the act of recording that fact visually, on your own personal chromosome map, so that segment is no longer just a name on a match list. It becomes a labeled piece of a much bigger picture.
Do this enough times with enough matches, and patterns start showing up. You will notice unidentified matches sharing a segment with a match you already placed, which is often a strong hint they descend from the same ancestor. This is how genetic genealogists solve brick walls that paper records alone cannot get through.
What You Need Before You Start
A DNA Test With Segment Level Match Data
Chromosome mapping only works with testing companies that show you the actual chromosome, start position, end position, and centimorgan count for each match. FamilyTreeDNA, 23andMe, MyHeritage, and Living DNA all provide this. Gedmatch does as well, once you upload a raw DNA file from any of those companies.
AncestryDNA is the exception. It does not give you match level segment data, only an overall relationship estimate, so matches from Ancestry alone cannot be painted unless that person has also tested with, or transferred to, one of the other sites.
At Least a Little Known Family History
You do not need a fully built family tree to start. You do need to know how at least one or two of your matches are related to you, since your first painted segments will anchor everything that comes after. A known first cousin, aunt, or grandparent is a perfect place to begin.
Setting Up Your Free DNA Painter Profile
Go to dnapainter.com and register for a free account. You do not need to pay anything to get started, and a free account gives you one full chromosome map along with access to most of the site's core tools.
Once you are logged in, go to the Dashboard and click the Chromosome Maps tab. From there, click Create a New Map.
You will be asked to enter a name and biological sex for the person the map represents. If this is your own DNA, use your own name. Biological sex matters here because it determines whether the map includes an X chromosome pair or a single X, which affects how X-DNA matches get interpreted later.
Once you save this, you will see a blank canvas made up of your chromosome pairs, numbered 1 through 22, plus your X chromosome. Each numbered chromosome shows two bars stacked together, one representing the copy you inherited from your father and one from your mother. Right now both bars are empty. Painting matches is what fills them in.
Getting Segment Data From FamilyTreeDNA
For this walkthrough, we will pull a shared segment from FamilyTreeDNA, since it is one of the most common sources beginners start with.
Log into your FamilyTreeDNA account and go to Family Finder Matches under your autosomal DNA results. Find the match you want to paint, the one you already know how you are related to, and select the checkbox next to their name.
Click the button to compare the relationship, which opens the Chromosome Browser. This shows a visual comparison of your shared segments laid out along your chromosomes, along with a table below labeled Detailed Segment Data.
That table is what you need. It lists the chromosome number, start position, end position, and centimorgan count for every segment you share with that match.
You have two ways to get this data into DNA Painter. You can highlight the entire table with your mouse, copy it, and paste it directly into DNA Painter in the next step. Or you can click the download button to save it as a CSV file and upload that instead. Either method works, and copy and paste is usually faster for a single match.
Painting Your First Match
Head back to your chromosome map on DNA Painter and click Paint a New Match, usually found near the top right of the page.
A form will open asking for the segment data. Paste in the table you copied from FamilyTreeDNA, or upload the CSV file if you went that route. DNA Painter will read the data and calculate the chromosome, start, and stop positions automatically, then show you a preview of where the segments will land.
Once the preview looks right, click Save These Segments to Your Map.
Deciding Maternal or Paternal, and Choosing a Color
This next screen is where the map actually becomes useful.
You will be asked whether you already know how you connect to this match. If you do, leave that option selected, since it unlocks a few more helpful fields. You will then fill in a name for the ancestor you both descend from, not just the match's own name. If your shared connection is your great grandmother, use her name, not your cousin's, since this is the label that will show up on the map going forward.
Next, choose whether the match is on your maternal or paternal side. If you know your mother is the parent this match connects through, choose maternal, and the segment will be painted onto the correct bar of each chromosome pair.
Finally, pick a color. DNA Painter will suggest one automatically, but it is worth choosing colors intentionally from the start. A common approach is grouping colors by grandparent, using shades of blue and green for your father's parents and shades of red and orange for your mother's parents. This makes the map much easier to read once you have dozens of matches painted instead of just one.
Click Save, and the segments will appear painted onto your chromosome map in the color you chose, sitting in the exact position that matches the data from FamilyTreeDNA.
If you do not yet know how a match connects to you, you can still paint them. Choose the option indicating you do not know the connection yet, and DNA Painter will ask for a group label instead of an ancestor name. Many people label these by surname or by whichever side of the family seems most likely, then come back and update it once the connection becomes clear.
Reading Your Map as It Fills In
After painting a handful of matches, patterns start to show up that are worth paying attention to.
When two unrelated matches paint onto the exact same, or an overlapping, segment on the same chromosome, that is called triangulation. It is a strong signal that both matches descend from the same ancestor as you, even if you only knew how one of them connected beforehand.
Gaps in your map are just as informative as filled sections. An empty stretch of chromosome usually means you have not yet found or painted a match for that ancestral line, which can point you toward which branch of the family tree needs more research.
Pay attention to where segments stop and start as well. A sudden change from one ancestor's color to another partway through a chromosome marks a recombination point, the exact spot where your DNA switched from one grandparent's genetic contribution to another's during inheritance.
Common Mistakes Beginners Make
The most frequent mistake is labeling the ancestor field with the match's own name instead of the shared ancestor's name. Doing this for a handful of matches makes the map confusing fast, since the whole point of the label is to show which ancestor a segment came from, not who you happen to be comparing yourself to.
A second common mistake is guessing at maternal or paternal side when you are not actually sure. If you are not confident, it is better to leave that field blank for now rather than paint it incorrectly, since a wrong assignment can send you down the wrong branch of research entirely.
The third mistake is picking colors randomly for each new match instead of building a consistent color system early. Going back and recoloring dozens of segments later is tedious, so it pays to plan your color groups before you paint your first real batch of matches.
What a Free Account Gets You, and When to Consider Paying
A free DNA Painter account gives you one complete chromosome map, which is enough for most people who only want to map their own DNA. You can paint matches one at a time using the copy and paste method described above at no cost.
A paid subscription, currently 55 US dollars a year, unlocks a few things that become useful once your research grows. It allows you to create up to fifty separate chromosome maps, which matters if you also want to map a parent, grandparent, or sibling who has tested. It also unlocks bulk import, letting you upload an entire CSV of matches at once instead of pasting them one by one, along with extra features like multiple WATO probability trees for working out unknown relationships.
For a first chromosome map, the free version is genuinely enough to get real value out of the tool.
Turning a Chart Into a Story
A finished chromosome map is satisfying to look at, all those colored blocks lined up along your chromosomes like a genetic quilt. But the real value shows up later, when a mystery match finally clicks into place because their segment overlapped with one you had already painted for a known ancestor.
That is the quiet payoff of this kind of research. A centimorgan count on a match list is just a number until you trace it back to an actual person, and once you do, it stops being data and starts being a name, a birth year, and eventually a story you can pass down.
That is really what genetic genealogy and family history work are both chasing after, in different ways. The DNA tells you who your ancestors were. The stories tell you who they actually were as people, which is exactly the gap Memoracy was built to close, one daily prompt at a time, so the people you are still able to ask do not become another name you only ever meet through a chromosome map.
Sign up and start your first story on Memoracy today.
