When asked about how database size affects ancestry results, David Nicholson, co-founder of Living DNA, told us, “The tests absolutely rely on the reference database. If you have Polish ancestry but there are no people in the database who are Polish, then what the test will do is show what the next closest group is next to Polish, like German or Eastern European ancestry.” Each ancestry DNA service has its own sample database and reference panel made of the DNA samples collected from their users and information collected from sources like the 1000 Genomes Project. The database consists of all this information collectively. A reference panel is made of certain curated samples with known family history and roots in a specific place. The services use insights gleaned from the reference panel to give you geographical ancestry results. In theory, a larger database leads to more information available to create a good reference panel, which then leads to better results for customers.  

In Newman’s view, the genie is out of the bottle with home genetic-testing kits. He says that while the kits could potentially provide data in the future, right now, they lack “clinical utility” – they look at genetic variants that, individually, have a very low chance of predicting specific health risks, as there are too many variables: “It’s like the Opportunity Knocks clap-o-meter, with some people further along the scale, and therefore more likely to get the condition and then people at the other end of the scale, who are unlikely to get it.”
If you are concerned about your data being sold, your concern may be valid. In the past, records have been sold and de-anonymized. It is possible for genetic information to be used to find the name of the individual the DNA came from. This can happen regardless of whether or not your name was in the database. This scenario has occurred in the past.

Most of this trait data tells you things you already know, like your hair and eye color, but it is fun to see them compared to your genetic relatives and the world at large. We also found it fascinating to learn more about how these physical traits are genetically determined. For example, finger length ratio is determined by hormonal exposure in the womb, with higher testosterone exposure resulting in a better chance of having a longer ring finger. 23andMe’s Health report for finger length ratio looks at 15 gene markers to estimate your likelihood of having longer ring fingers or index fingers.
So from that perspective, if DNA testing for fun and to find potential cousin matches is something you are considering, then wait for when they have a cheap special offer available. If you want a proper ethnic breakdown, either use the raw DNA file and upload it elsewhere or use one of the more accurate providers. Note they only do autosumnal DNA testing and NOT Y-DNA testing so you will need to use another service for that.
Most of the services we tested use genotyping to read your DNA. Genotyping looks for specific markers in your genetic code. For something like ancestry testing, genotyping is effective because it identifies known variants in your DNA. Scientifically speaking, genotyping’s weakness is that it can only recognize previously identified markers. This is one reason DNA tests’ accuracy relies so heavily on the DNA database size; there must be enough information available and identified genetic variants in the database to recognize new customers’ markers.
The spit is for one of the home genetic-testing kits I’m sampling. A growing number of these kits (brands such as 23andMe, DNAFit, Thriva, MyHeritage DNA, and Orig3n) promise to unlock the mystery of your genomes, variously explaining everything from ancestry, residual Neanderthal variants, “bioinformatics” for fitness, weight loss and skincare, to more random genetic predispositions, denoting, say, the dimensions of your earlobes or the consistency of your earwax.
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