DNA Painter, a DNA analysis tool created by Jonny Perl, was the well-deserved winner of the 2018 RootsTech DNA Innovation Contest. Jonny’s creation effectively meets key needs for genealogists as they engage in genetic analysis and interpretation.
Evaluating Amounts of Shared DNA
One of the first approaches employed by genealogists in genetic analysis is evaluation of shared DNA between known and unknown genetic cousins. Some amounts of shared DNA are more likely for certain levels of relationship than they are for others. Each of the DNA testing companies are necessarily conservative in the relationship estimates they publish, but analysis of shared centimorgans (cMs) can give better indications of likely levels of relationship, thus guiding interpretation and research prioritization. Before DNA Painter, many relied on the Shared cM Project and/or the probability chart published in the AncestryDNA Matching Whitepaper to better interpret amounts of shared DNA. While the Shared cM Project reports real data and shows ranges of likely relationships, it does not include probabilities of relationship levels given an amount of shared DNA. Meanwhile, the AncestryDNA White Paper chart shows these probabilities, but is based on simulated data and is difficult to interpret because of its logarithmic scale.
DNA Painter’s “Shared cM Tool v4” combines the best of both resources. By entering a number of shared cMs, researchers can obtain detailed probabilities of various levels of relationship.
These probabilities are obtained from computational analysis of the published graph and are much more accurate than eyeball estimates. At the same time, all relationships in which a specific number of shared cMs have been observed are highlighted on the most recent version of the Shared cM Project chart. A related tool enables exploration of joint probabilities as researchers test multiple comparisons within the context of a set of hypotheses. When utilizing these resources, keep in mind the following cautions:
- Genetically equivalent relationships (like first cousins, great aunts, half uncles and great grandmothers) are grouped in relationship categories based on the number of common ancestors and the number of generational steps.
- Relationships more distant than the level of fourth cousins are grouped into a single distant cousin category.
- Probability estimates for amounts of DNA lower than 40 cMs were extrapolated by extending the Ancestry Whitepaper graph’s curves and may not be as exact as those that were simulated.
- There is a possibility of entering a percentage rather than a number of shared cMs, but centimorgan to percentage conversions are not exact given the logarithmic nature of centimorgan measurements and probabilities based on percentages may not be as accurate.
- Joint probabilities assume independence and not all genetic relationships are independent. For the best results seek comparison against genetic cousins from unique descent lines of a common ancestor.
Overall, these resources provide invaluable insight for researchers and clients as we evaluate the likelihood of documented and proposed relationships for known relatives and estimate potential relationships for unknown relatives.
Chromosome Mapping Made Easy
DNA Painter also makes chromosome mapping readily accessible to most researchers. Previously, creating chromosome maps required extensive knowledge of spreadsheet software, exact headings and formats for inputs, time consuming uploads and/or cumbersome processes that made this approach inefficient for professionals, out of reach for others and cumbersome for all. DNA Painter overcomes many of these obstacles.
It permits creation of multiple profiles for different map subjects. Painting segments is as simple as copying and pasting segment data from GEDmatch, MyHeritage, 23andMe, or Family Tree DNA into the entry field and attaching any notes, comments, or considerations that the creator may wish to add. Segment data is easily assigned to existing or new relationship groups. If the origins of shared DNA with a genetic cousin are unknown, DNA Painter is designed to enable rapid hypothesis testing against other known and assigned segments. Assignment of segments, matches and relationships is easily editable and duplication options make it simple to create multiple backup maps at different stages of the mapping process. Alternatively, duplicated maps can act as a starting or comparison point for other map subjects. DNA Paintings are stored online, are easily accessible from anywhere and easily shareable with anyone. DNA Painter transforms chromosome mapping from the cumbersome, monotonous and sometimes discouraging task it was in the past to an addictive, fun and immensely informative pursuit.
DNA Painter offers wonderful additions to the genealogist’s arsenal of resources. The available tools for shared cM evaluation build upon the best elements of previously available resources and the painting platform launches chromosome mapping to a whole new level of ease and usefulness. Give it a try, we think you will be pleased.
The Legacy Tree Genealogists team is uniquely qualified to assist in the interpretation and exploration of DNA test results as part of larger family history stories. If you have questions about genetic genealogy research and using DNA to extend your family history, we can help! Contact us today to request a free quote.
*This article originally published in the September 2018 APGQ is reprinted with permission
 Blaine Bettinger, “August 2017 Update to the Shared cM Project,” The Genetic Genealogist, 26 August 2017 (https://thegeneticgenealogist.com/2017/08/26/august-2017-update-to-the-shared-cm-project/: accessed May 2018).
Catherine A. Ball, et al., “Figure 5.2,” AncestryDNA Matching White Paper: Discovering genetic matches across a massive, expanding genetic database, page 32, dna.ancestry.com, accessed May 2018.