Men have an X and a Y (chromosome) that are paired together. Women don’t have the Y, they just have two X’s. A child’s genes come from a mix up and recombining of the two parents. So a girl child will still end up with two X’s but some bits of them will come from the father’s X and some from the mother’s. A boy child on the other hand may have some bits of X from both mother and father, but his Y will have just come purely from his father – virtually unchanged. That makes Y-DNA such an exciting possibility for genealogy where you want to follow the paternal (surname) line. You could expect that Y-DNA will therefore pass virtually unchanged from father to son through the generations, meaning that the Y-DNA of a man’s g-g-g-g-grandfather will look very much like that of his own Y-DNA – with some little changes.

While 23andMe does offer DNA relative matching and some tools to compare your genes to your DNA relatives, it doesn’t have robust genealogy tools, as its focus rests more in personal discovery and exploration. To that end, 23andMe has an optional health upgrade that provides reports on DNA traits like hair color and genetic predispositions to certain illnesses and diseases. It is the only DNA test with FDA approval for testing genes linked to conditions such as Type 2 diabetes, certain types of cancer, late-onset Alzheimer’s disease and Parkinson’s disease. If you’re interested in the health portion of the test, we recommend buying the Health + Ancestry test together, as this option costs less than upgrading later.

For the uninformed, this is the best discussion on the subject of DNA that I have ever seen. I have been trying to determine who my great great grandfather is for years. I’ve tested with Ancestry and Family Tree DNA, hired ProGenealogists with Ancestry (twice), and still can’t determine who he is. I truly don’t know where to go now. The genealogist that consults with Finding your Roots works for a company that doesn’t do individual research. Who else does the genetic genealogist research that they do?
The test kit gathers saliva from spit. It offers a free family tree tool to which users can contribute their specific results. You can also download your full DNA profile and import that data into another tool -- but it doesn't offer a chromosome browser, so you can't really do DNA segment comparisons. Given this, if you're a true DNA geek, Ancestry may not be the service for you.
Some concerns about the ultimate efficacy of certain home tests seem to emanate from the industry itself. I did a telomere-measuring test (a mouth swab) by Titanovo, based in north Colorado, which came back saying that my telomeres were too short, putting me at 10 biological years older than I am. However, when I contacted Titanovo, it explained that it had stopped telomere measuring and was now concentrating exclusively on its DNA-utilising “bioinformatics” health, fitness and wellbeing website (analysing client data from other genetic testing sites).
After taking a DNA test for ethnicity, many ancestry companies will give you the option to contact their other customers, providing you share sections of your autosomal DNA with them (meaning that you’re related to these individuals to a greater or lesser degree). The companies that do this maintain ‘Family Finder’ databases, and the people you’re related to are usually referred to as ‘matches’. The three largest companies that do this are Family Tree DNA, Ancestry.com and 23andMe, and as part of the results that they provide, you’ll be able to see a list of these living relatives ranked according to how closely you’re related to them.

AncestryDNA, 23andMe, HomeDNA, Living DNA, and MyHeritage DNA all provide reports of your ethnicity, some showing maps of where your ancestors lived along with information about the particular countries and regions. National Geographic goes further back, pinpointing where in Africa your ancestors came from and tracing migration patterns through to near-present times. It's less about your personal genetic makeup and more about who your ancestors were and how you're connected to the beginning of civilization.
Bill Newman, professor of translational genomic medicine in the Manchester centre for genomic medicine at the University of Manchester, and chair of the British Society of Genetic Medicine, says that such tests in this context simply don’t make sense and that, usually, telomere testing would only be used in in-depth studies of ageing and diseases associated with ageing. “There’s some really brilliant work going on, by some of the best biologists in the world,” says Newman, citing Elizabeth Blackburn, who won the 2009 Nobel prize for medicine for her work on telomeres. “But there’s no evidence whatsoever that measuring a person’s telomeres gives any indication about their health – or beauty, intelligence, or anything else that might be listed on these sites.”
Your DNA information is gathered using saliva capture, which, once analyzed, is stored forever on 23andMe's servers. The service also provides for a chromosome browser and comparison, as long as any possible matches approve your access. The service's matrilineal and patrilineal line testing can geolocate your DNA ancestry in more than 1,000 regions. 

With a 16-day turnaround, MyHeritage DNA was one of the first companies to send back our test results, but I found the contents of my ancestry report to be a bit off, especially when compared to my geographic ancestry reports from other companies. I was born in Korea and therefore expected at least a little of my Korean heritage to make it onto my ancestry map, as it did with other services, but MyHeritage didn’t report any Korean heritage. 

And a final note: be on the alert for surprises in your DNA – sometimes its as simple as realising that what you thought was a surname that had come down through the male line, has actually been taken from a female at some point who kept her maiden name (which means the DNA signature will match the surname of the father of her children, and not the surname the child was given). Sometimes the man who is believed to be the father just isn’t – and that will show by his real sons having a different DNA signature to the ones fathered by another man. Often these NPE’s (non-paternal events) will be many generations back, but they could be much closer.
So what are you waiting for? If your family’s genetic signature hasn’t yet been tested, how about considering contributing to the genealogical record and resource for your family by finding one or two men to take a Y-DNA test. If you are a male S-NN-T descendant then please check out the Sinnott/Sennett (and variants) surname project at familytreeDNA.com – you even get a discounted rate for the Y-DNA37 test if ordered through the project. http://www.familytreedna.com/group-join.aspx?Group=Sennett
Consult a doctor on any health data: Cancer. Leukemia. Heart disease. Alzheimer's. There are a lot of scary afflictions out there, and your DNA testing may well indicate which ones to which you are genetically predispositioned. But the data from DNA testing exists in isolation. You should consult your doctor to explore the data from any of these tests. They'll help you determine how to implement any lifestyle changes or followup testing as a result, if it's worth doing so.
As it happens, most of the data on 23andMe seems harmless and fun. There are the “Neanderthal variants” (I have fewer of them than 58% of 23andMe customers, thank you very much), the bizarre earwax/earlobes-type data and, apparently, I have the muscle composition generally found in “elite athletes” (fancy). On the downside, my lineage isn’t as exotic as I’d hoped: 99.1% north-western Europe, of which 71% is British/Irish, with just 0.01% “Ashkenazi Jewish” to offset the genetic monotony. At £149, the 23andMe kit isn’t cheap and I’m quite tempted to demand a recount.
Rachel, it’s been a year since you posted your query. Perhaps you have your answers? In case not, here are a few suggestions. Since you are an adoptee, perhaps with no knowledge of your biological family, you probably are most interested in details there, while your ethnic makeup is a very minor concern and where most DNA services give similar results anyways. Maybe your goal is to locate your birth parents? If that’s all true, then buy an AncestryDNA kit, as they have 10 million DNA profiles in their database, which is more than all competitors combined. The more profiles to DNA match against the more matches you’ll get to your biological relatives. Next download your raw Ancestry DNA data, and then upload it for free into MyHeritage (2.5 million DNA profiles), FamilyTreeDNA (1 million DNA profiles), GEDmatch (1 million DNA profiles), LivingDNA (unknown database size), and DNA.land (0.15 million DNA profiles). That’s almost 5 million more DNA profiles to match against. Combined with AncestryDNA that’s about 15 million profiles. If lucky you may match to a 2nd cousin or closer relative which with luck could lead to your birth parents, definitely will match to a few if not many 3rd cousins and 1000s of 4th or more distant cousins. If you change your mind and decide purchasing a second DNA kit is worth the expense, then buy a 23andMe DNA kit, which adds 5 million more DNA profiles to match against. Hope these suggestions were useful. Good luck.
The DNA tests we reviewed either require a saliva or cheek cell sample. Saliva-collecting kits include a tube that’s marked with a fill line and sample number. The tube often has a liquid-filled cap with a stabilizer that acts as a preservative to protect your DNA from degradation during transport. Cheek swab sample kits include one or two swabs for scraping the insides of your cheeks for 30 seconds to a minute to collect cheek cells and some sort of container to place the used swabs into after collection. This prevents contamination. Our testers found upsides to both types of kits but generally preferred saliva collection kits, even though they took longer.
There's a lot you can learn from a DNA test. In addition to deepening your understanding of ancestry, some services will introduce you to relatives around the world or shed light on your predisposition to specific health issues and diseases. Here we present to you our roundup of the nine top DNA testing kits and services -- what they offer, how they work and how much they cost. 
AncestryDNA has been responsible for taking DNA testing mainstream, and they now have the world’s largest autosomal DNA database. The test benefits from a number of innovative and sophisticated features such as shaky leaf DNA hints integrated with family trees, DNA Circles, Genetic Communities and New Ancestor Discoveries. A subscription is required to access some of these features and to view the full trees of your matches. The lack of a chromosome browser and matching segment data is a big disadvantage for advanced users who are interested in chromosome mapping. Many of the people now taking the AncestryDNA test are lured in by the biogeographical ancestry reports, but are not interested in communicating about genealogy. However, the test is encouraging an interest in genealogy in a subset of this market.
Living DNA supports 80 geographical ancestry regions, 21 of which are located within Britain and Ireland alone, making it a great DNA test for people wanting to delve deep into their British heritage. Of course, it also covers 60 regions outside of the British Isles, and is expanding its efforts to bring the same level of detail to other world regions.
The results of mixed DNA profiles may therefore provide reduced match probabilities when compared with non-mixed profiles. It may be possible for a scientist to be able to assess the relative amount of DNA contributed by different donors in a DNA mixture. If one person has contributed a clear and distinct majority of the DNA detected, that part of the profile may be referred to as the “Major Contribution”.

23andMe is a bit different in that many people have tested with their company for the health results and are not necessarily interested in genealogy or matching with relatives, even if they opted into this feature. That doesn’t mean you won’t get a good response when reaching out, but it may be less common than with the other testing companies. Recently 23andMe has been placing more focus on genealogical testing, however, so this is may be shifting.

The only patients having their genome sequenced are those with certain cancers or rare diseases. In some cases, family members may also be asked to participate. To take part, a patient must first be referred by a consultant, before being taken through an extensive consent process to ensure they know what participation in the project means. As well as the genome sequence, Genomics England asks for access to a patient’s lifetime medical records so that links can be made between their genetics and their individual disease. The NHS has made it very clear that, for many participants, taking part in this project won’t help them treat their disease. But it is hoped that the information they provide will go on to help treat others in the future.

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.
Written out the base pairs in DNA make a sequence, e.g. A T A T C G C G T A A T G C. More than 99.9% of those bases are the same in all people. The order, or sequence, of the letters determines the information available for building and maintaining an organism, similar to the way in which letters of the alphabet appear in a certain order to form words and sentences.
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