Autosomal DNA Test Results: Using Ethnicity Estimates to Generate Genealogical Hypotheses
The material in this autosomal DNA blog article was originally published in the October-December 2021 issue of NGS Magazine. It is updated and republished here with permission.
Autosomal DNA test results at the major genetic genealogy testing companies (23andMe, Ancestry, Family Tree DNA, LivingDNA, MyHeritage) include two main elements: ethnicity admixture estimates and genetic cousin match lists.
While genetic cousin match lists are the most helpful resource for solving genealogical problems utilizing autosomal DNA, ethnicity admixture estimates can provide important context and clues to aid the interpretation of DNA matches.
When carefully analyzed, ethnicity estimates can sometimes aid in forming hypotheses that can be tested through more in-depth research in genetic cousin match lists.
Even so, ethnicity estimates are still estimates, and will continually be refined as company reference panels and algorithms improve. These ethnicity estimates should be considered within the context of all available evidence, including genetic cousin relationships.
Basic Interpretation of Autosomal DNA Ethnicity Admixture Estimates
With few exceptions, each individual inherits 50% of their autosomal DNA from their mother in 22 chromosomes and 50% of their autosomal DNA from their father in 22 corresponding homologous chromosomes (meaning that they are similar in size, shape, and organization of genetic material). Since you can inherit only 50% of your DNA from each parent, if your ethnicity admixture estimate reports approximately 50% from one region and approximately 50% from another unique region, it could indicate that you have one parent from each region. Meanwhile, if you have significantly more than 50% admixture (more than 60-70%) from a single region, it could indicate that both of your parents had at least some ancestry from that region.
While each company can typically differentiate genetic admixture at the continental level, it is more difficult to distinguish between closely related populations.
If a test subject has significantly more than 50% admixture from a single region, it could indicate that both parents had at least some ancestry from that region. In this case, the test subject has significant British Isles ancestry on both sides of her family tree.
You can read more about understanding Autosomal DNA in our article here: How to Understand Your Closest Autosomal DNA Test Matches.
Even so, use caution when making these preliminary observations, particularly if your parents have ancestry from different countries in the same general area. For example, if you have one parent from Ireland and another from Japan, you will likely have a fairly even split in ethnicity admixture estimates.
Meanwhile, you have one parent from Norway and another from Germany. In that case, you may have higher than expected estimates of Scandinavian admixture, German admixture, or other populations in Northwestern Europe because of the proximity and historical association of those two populations.
These observations can help provide the context in cases of adoption, unknown parentage, or misattributed parentage, but can even be helpful for more distant genealogical research problems.
Making Sense of the %
If you have a unique ethnicity admixture region that stands out from the rest of your estimate, then the percentage might give clues to estimate the distance to the ancestral source of that DNA. Each person inherits 50% of the autosomal DNA from each parent, about 25% from each grandparent, about 12% from each great-grandparent, and about half again every generation back in time.
Therefore, if you have approximately 25% Jewish admixture, you were surprised that it might come from an unknown grandparent. If you have 4-8% Iberian admixture, it could come from a Spanish or Portuguese second great-grandparent.
However, ethnicity estimates need not originate from a single ancestor. If you have 25% Aboriginal ancestry, you could just as easily have two Aboriginal great-grandparents from different ancestral lines as a single grandparent with Aboriginal ancestry.
If a test taker’s ethnicity admixture estimate reports approximately 50% from one region and approximately 50% from another unique region, it could indicate that the test subject has one parent from each region. in this example from MyHeritage, the test taker’s mother was completely Danish fitting with her 44% Scandinavian admixture.
Using an Absence of Information to Find Answers
Even the absence of a unique admixture estimate can aid in forming hypotheses in genealogical research. For example, if you ultimately attempt to identify your unknown second great-grandfather, your DNA test results reveal you have a 100% British admixture. You could assume that your unknown second great-grandfather was also probably from the British Isles.
While we inherit autosomal DNA from many of our ancestors across many ancestral lines, not all of our distant ancestors contribute to our inherited set of DNA.
Even so, each of us should inherit at least some DNA from each of our fourth great-grandparents. Therefore, if you have a family story that your great-great-grandmother was “full-blood Cherokee,” yet you have no Native American admixture, it could indicate that your family story is inaccurate.
Want to know what to do next? You can learn more in our article Eight Steps to Pursue With New Autosomal DNA Test Results.
Ethnicity Chromosome Paintings
In July 2021, Family Tree DNA announced that they would soon be releasing a chromosome ethnicity painting. Ethnicity paintings are helpful for formulating hypotheses based on number, size and position of segments assigned to particular ethnicity regions.
In addition to ethnicity admixture estimates, 23andMe also provides an ethnicity chromosome painting showing which DNA segments correspond to different ethnicity regions. In September 2021, Family Tree DNA began offering a similar feature, and in July 2022, AncestryDNA also began providing a chromosome painting in connection with their ethnicity reports. They also began dividing ethnicity admixture estimates by parent. These representations can offer additional insights beyond the information provided by the percentage reports alone.
Autosomal DNA tests query thousands of markers across a test-takers genome and report two values for each marker: a value from the paternal chromosome and a value from the maternal chromosome. At any given site, however, it is impossible to tell which value corresponds to the maternal chromosome and which corresponds to the paternal chromosome. Further, it is difficult to determine which value on a consecutive marker corresponds with the same chromosome copy as the first or second value on the previous marker.
23andMe processes DNA data to “phase” test results to construct ethnicity chromosome paintings. Through the phasing process, 23andMe attempts to determine which consecutive markers belong with each other on one chromosome copy and which marker values belong together on the other chromosome copy. Family Tree DNA and AncestryDNA utilize similar approaches.
Want to learn more ways to use chromosome paintings? Read our article 5 Ways to Use the DNA Coverage Estimator Tool at DNA Painter.
How To Determine Maternal or Paternal Chromosomes
Once DNA test data has been phased, it is chopped into smaller chunks or windows and assigned to reference populations. The 23andMe results show these assignments in the chromosome painting. Since it is not possible to know which DNA is paternal and which is maternal without additional information, the top chromosome in each representation is not necessarily paternal. The bottom is only sometimes maternal. Further, since the DNA is chopped up before being assigned to regional categories, it is possible and often occurs that the representation of one chromosome copy is a combination of maternal and paternal DNA.
Therefore, just because a particular ethnicity admixture assignment appears on the top chromosome version in some pairs and on the bottom chromosome version in other pairs does not mean that both parents have admixture from that region.
Also, just because a particular ethnicity admixture assignment appears on the top version of a single chromosome pair and in a different region on the bottom of the same chromosome pair does not mean that both parents have admixture from that region. Even with these caveats, chromosome paintings can reveal important information regarding your ancestry.
If one complete version of every chromosome pair is assigned to one ethnic region and the other complete version of every chromosome pair is assigned to another ethnic region, it indicates that your father is of one ethnicity and your mother is of the other, rather than having a mix of ancestors from both regions on both sides of your family tree. Suppose there are several chromosomes where large overlapping regions on both chromosome copies have been assigned to the same ethnic region.
In that case, it can indicate that both of your parents have at least some ancestry from that region. If just a few large chunks of DNA are assigned to a particular ethnic region, it can suggest that you have only one (or perhaps a few) recent ancestor(s) originating from that area. Meanwhile, suppose the assignments for a unique ethnic region are dispersed across the genome in many small segments. In that case, this can indicate that you have multiple more distant ancestors from that region.
The Difference Between X-DNA, Y-DNA, and Mitochondrial DNA
Information about X-DNA, Y-DNA, and mitochondrial DNA can also aid in interpreting chromosome paintings by suggesting which ancestral lines may or may not be the ancestral source of a particular ethnicity admixture assignment. Males inherit X-DNA from their mothers, and females inherit X-DNA from their mothers and paternal grandmothers. If a chromosome painting shows that a unique ethnicity has been assigned to all or a portion of a male’s X-DNA, then the source of that DNA is likely from that individual’s maternal ancestry. If a female test taker’s X-DNA carries segments assigned to a unique ethnicity, it may come from her maternal or paternal grandmother’s ancestry.
Males also inherit a Y chromosome from the father and his direct paternal ancestors. Y-DNA signatures are grouped based on their similarity into “haplogroups,” some of which are geographically or ethnically specific. Suppose you have a high percentage of Northwestern European DNA in your admixture estimate and a Y-DNA haplogroup most commonly found in Western Europe. In that case, it could suggest that at least part of your European admixture originates from your direct paternal ancestors.
All individuals inherit mitochondrial DNA (mtDNA) from their direct maternal ancestors. As with Y-DNA, mtDNA signatures are categorized into haplogroups which can be geographically or ethnically specific. Suppose you have African admixture in your ethnicity estimate and an mtDNA haplogroup commonly found in Africa. In that case, it can suggest that your African admixture originates at least in part from your direct maternal ancestors.
Just because a particular ethnicity admixture assignment appears on the top version of a single chromosome pair and in a different region on the bottom version of the same chromosome pair does not mean that both parents have admixture from that region. In this example from 23andMe, the test taker has Jewish admixture (green) and Sub-Saharan African (shades of pink and purple) admixture in different regions represented on both chromosome copies even though both of these ethnicities are from the test taker’s paternal ancestry.
What Next? Pinpointing the Source of Unexpected Autosomal DNA Test Results
While ethnicity admixture estimates and ethnicity chromosome painting can help formulate hypotheses for further investigation, pinpointing the ancestral source(s) of a unique or unexpected admixture assignment most often requires additional consideration of genetic cousins. Identifying genetic cousins who also carry a unique or unexpected ethnicity admixture assignment and then identifying their relationships to each other and to you can help, as can searching for genetic cousins with 100% admixture from a single region and considering their shared matches. At 23andMe, you can download the segment data for the ethnicity chromosome painting and correlate this information with segment data from 23andMe and other companies to identify which genetic cousins share the same ethnicity admixture region and the same segments of DNA.
While not the most critical element of autosomal DNA test results for solving research questions, ethnicity estimates provide an important broad context for genealogical investigation and enable the formation of hypotheses that can be further explored through careful analysis of genetic cousin match lists, documentary evidence, and segment data.
If there are several chromosomes where large overlapping regions on both chromosome copies have been assigned to the same ethnic region, it can indicate that both parents have at least some ancestry from that region. In this example from 23andMe, the test taker has European (blue) and African (pink) admixture on both their paternal and maternal sides as evidenced by large overlapping regions on both chromosome copies.
If you need more help interpreting your Autosomal DNA test results, you can reach out to our team of professional genealogists for more assistance.