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.  
By comparing the arrangement and distribution of the peaks, it is possible to compare profiles of known origin with a profile from a crime sample. If the two profiles match, databases are used to estimate the probability of obtaining a matching profile from a person selected at random; this is referred to as thematchprobability. Closely related individuals are more likely to share DNA profiles than more distantly related individuals.

Which is all very well, but do these kits work and deliver the service they promise and what about the wider ethics and implications of home genetic testing? Is it always wise for generally under-informed, under-prepared consumers to meddle in the highly complex, nuanced arena of genetics, risking confusion, complacency or even outright panic and anxiety when confronted with ostensible “bad news” (which may not even be true)?
Costs vary depending on the company you buy from. For example, the three most popular DNA ethnicity tests are undertaken by 23andMe, Family Tree DNA (FTDNA) and Ancestry.com. They all analyse autosomal DNA to report on your ethnic mix: 23andMe’s costs £149, FTDNA’s (named the ‘Family Finder’ test) costs £60 and Ancestry.com’s (named ‘AncestryDNA’) costs £79. However, it’s worth bearing in mind that 23andMe’s test also includes a Y DNA analysis and a mitochondrial DNA analysis, so if you’re interested in your paternal and maternal lineage (discussed below), this may be the more cost-effective choice!
FTDNA offers Y-DNA (y chromosome, fatherline, men only) and mtDNA (mitochondrial, motherline, everyone) tests. These are separate offerings from the Family Finder test and can be very detailed, depending on the test and option you choose. 23andMe offers mtDNA and Y-DNA as part of their main Ancestry offering, but the results are more limited. Read more about these types of tests here.
All this comes into sharp focus with the comprehensive kits such as the one provided by 23andMe: the one I drool into a tube for (incidentally, 23andMe doesn’t test for Huntington’s disease). Most people, like myself, have a low understanding of genetic variants, what phrases such as “higher risk” or “probability” actually mean or how to interpret our results correctly. Is it right that ordinary members of the public must navigate potentially frightening and/or misleading results alone?
Some of our reports are about serious diseases that may not have an effective treatment or cure. Some people may be upset by learning about personal risks, and risks for family members who share DNA. 23andMe will not share your personal information with an insurance company without your explicit consent. Learn more about third party information sharing here.
Most direct-to-consumer DNA test companies warn that the tests may reveal things you wish you didn’t know about your family. For example, you could find out that one of the people who raised you isn’t your biological parent or that there’s an entire branch of your family you didn’t know about. There isn’t a way to prepare for a shock like that, but you can opt out of a company’s family-matching services if you’d rather not know.
Starting at $79, the company's DNA test kit is competitively priced and covers the basics: A simple cheek swab will give you an analysis of your ethnic origins and the identification of relatives who share your DNA. In addition to MyHeritage's free basic subscription, which will let you assemble a family tree up to 250 people, there are other packages that accommodate larger trees, advanced DNA features, and more robust research tools. The company allows you to upload test data from other companies.
Generally speaking, those people who have tested with FTDNA, AncestryDNA or MyHeritage DNA have done so for genealogical purposes (even if it is only curiosity about their family’s past) so the response rate from contacted matches is fairly decent. Oftentimes matches are open to being contacted by relations and are eager to compare trees. This is, of course, not always the case, but we have found it to be true for the most part.
Our Ancestry Service helps you understand who you are, where your DNA comes from and your family story. We analyse, compile and distill your DNA information into reports on your Ancestry Composition, Ancestry Detail Reports, Maternal & Paternal Haplogroups, Neanderthal Ancestry, Your DNA Family and provide a DNA Relatives tool to enable you to connect with relatives who share similar DNA.
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.
Once your genetic information is out there, it’s difficult to undo. Also, once you know something about yourself, it’s impossible to forget. Revelations such as having different parents than you expected or finding unknown half-siblings are difficult to process at any age, but it’s particularly troubling for kids. However, you can always simply opt out of family matching features.
The Y chromosome is a special chromosome, passed on from fathers to their sons, while mothers pass on mtDNA to both their sons and daughters. But mtDNA dies with men and so it survives only in the female line. This means that a man’s lineage can be followed along both paternal and maternal lines, while in a woman only her maternal or mtDNA line can be followed.