I’ve written before about lowering expectations for genetic genealogy, particularly in the context of ethnicity estimates. In the Lineage Research space at Quora, a lot of questions are asked about why certain ‘known’ ancestries don’t show up in DNA test results. Amidst this confusion, I feel that this topic certainly hasn’t yet been exhausted and compelled to address it once again. Feel free to share this newsletter to anyone it may help!
Firstly, it’s important to have realistic expectations and, for that, the process of what is being done in a DNA test needs to be understood.
The commercial DNA testing companies (e.g., Ancestry, FamilyTreeDNA, 23andMe, etc.) use gene chips/arrays. These are uniform and standardized for specific single point mutations known to exist in the human genome. For the 0.1% of DNA that differs between humans, there are thousands of these potential points. Each testing company looks at a different number of them, and potentially different ones altogether, making each test a unique measure. You can get different results from each company simply because of the tests themselves.
This technology is very accurate. If you have the appropriate sequence to bind the chip at a specific point, then you have that particular allele (the version of the mutation being looked for). However, we each have two copies of each autosomal gene (the non-sex chromosomes), so it is also possible that if you have two different alleles, you may may get, what I’ll call for simplicity, a false negative. So though the technology is accurate, the results may be slightly different if you take the test with the same company a second time, simply because of your genetics (or if they’ve changed the chip they use - both Ancestry and 23andMe have done this over the years). You also need to note that there are three different types of genetic tests for genealogy - autosomal (i.e., Ancestry), mitochondrial (maternal line only), and Y (males only).
The results at this point are simply yes/no on whether the DNA sample provided matched the allele on the gene chip. It’s basic data fed into the company’s software so it can be compared to the results from reference populations. These are collated results or averages from groups that represent ethnic populations or geographic regions. These are people living today (or at least recently) who claim ancestry in the area where they live (or the ethnic group - it depends on the testing company). These reference populations differ by testing company based on the samples they’ve received and are outlined in the FAQ or Help pages of each company’s website.
This is why results differ between companies.
DNA ethnicity estimates are not ancestral comparisons. They are completely dependent on the self-reporting of the reference population and the software the company uses for comparisons. It’s also why the results change every now and then as the company gets more people sharing their information with them.
So, what is DNA testing good for? The familial matches on Ancestry are, for the most part, reliable and can help fill in recent generations of your family tree. The Y-DNA lineage research and mitochondrial lineage research are also helpful in bridging gaps left by war and record loss. Using GEDMatch and WikiTree, the results can help triangulate which family line you descend from as well. They keyword being “help” - this should all be used in conjunction with vital records, family histories, and other traditional research materials.
Despite its limitations, genetic genealogy can be helpful. Just don’t put too much stock in ethnicity estimates.
For more information on where to start with genetic genealogy, I wrote about it previously on Medium.