DNA Painter and Chromosome Mapping: A Genealogist's Tool

DNA Painter is the third-party tool most serious genetic genealogists use once a kit has been sitting in their account for a while. It does one thing well: it lets you paint shared DNA segments onto a map of your chromosomes and label each segment with the ancestor it came from. Over time, that map tells you which chromosome regions you inherited from each branch of your tree.

We are not affiliated with DNA Painter. It is a paid web tool with a free tier that handles a single profile, which is enough to learn what it does before you commit.

What chromosome mapping actually means

You inherit your DNA in chunks. Each chromosome you carry is a mosaic of segments from your four grandparents, eight great-grandparents, and so on back. When a DNA match shares a segment with you on, say, chromosome 7 from position 30 million to position 55 million, that segment came from a common ancestor. If you can identify the ancestor, you can paint that segment with their name.

Do this with enough matches and you build a personal map showing which regions of which chromosomes trace to which lines of your tree. The practical payoff is that when a new match shares a segment in an already-painted region, you can often guess which branch of your family they belong to before you even open their tree.

What you need before you start

DNA Painter takes segment data from any company that offers a chromosome browser. That includes 23andMe, MyHeritage, FamilyTreeDNA, and Living DNA. AncestryDNA does not offer a chromosome browser, which is why many Ancestry users upload their raw data to MyHeritage or GEDmatch before working with DNA Painter. Our guide to combining DNA tests covers that workflow.

For a refresher on what centimorgans and segments are, see our centimorgan explainer and the shared DNA chart.

A practical workflow

A common starting point is to paint segments shared with a known close match. If your maternal first cousin tests, every segment you share with them came from your shared grandparents. Label those segments with the maternal grandparent couple. Repeat with a paternal cousin, and roughly half your chromosomes start to fill in.

From there you work outward. A second cousin lets you go a generation further, assigning segments to specific great-grandparents. By the time you are working with third and fourth cousins, you are confirming which specific ancestral couple a segment traces to.

This is where triangulation becomes important. A segment is only safely assigned to a particular ancestor when three or more people sharing it can all be traced back to that ancestor through documentary genealogy.

What DNA Painter is good at, and what it is not

It is excellent at organising matches and at quickly answering “which branch is this person from?” once you have enough segments mapped. It is not a search tool. It will not find unknown relatives for you, though it will help you place them once you find them.

For adoptees and others without known close matches to seed the map, finding unknown relatives usually has to happen first, and DNA Painter comes in later. For genealogists breaking through brick walls, see using DNA to break brick walls.

DNA Painter has other modules too, including a “What Are the Odds” tool that helps adoptees evaluate which tree position a tester likely occupies. Blaine Bettinger’s writing at The Genetic Genealogist is the reference material most users learn the methodology from.

Once you start mapping, the map becomes a permanent reference that gets sharper with every new kit added to the family.

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