Some DNA analysis uses the Low Copy Number(LCN) method. This is a modification of the more commonly used SGM Plus method of analysis. The advantage of LCN analysis over standard SGM Plus is its extreme sensitivity; however this is also a disadvantage. The effects of cross contamination are more prevalent in LCN analysis, and due to various effects observed when amplifying very small amounts of DNA any LCN profile should be interpreted with caution.
Companies differ in terms of which reference populations they use. Some companies will create their own reference populations, while others will use populations identified in published studies. For example, 23andMe produce their own reference populations by sampling their customers (as long as the grandparents of those customers were all born in the same country). They then combine this data with public population data, produced by projects such as the Human Genome Diversity Project.

If you're creeped out by how much information Facebook, Google and Amazon have on you based on your online browsing habits, just remember that these DNA testing services are getting what is effectively your medical history. Make sure of their policies before turning over that valuable data. Also, even if you don't share your DNA with a service, your familial DNA data may be available if a relative shared their genetic material. The privacy issues can get very complex.
I can’t help you with your question Robin, but you make a good point. I have had my DNA tested (only with MyHeritage so far) and the “North and West European” part is so broad (it could be anything from France, Belgium, the Netherlands, Luxembourg, Germany etc but it would have been important to have more detail as it is really what I would have loved to know more about) and then 0.8% Middle East…
Three of the companies, MyHeritage, Ancestry and FTDNA, use the Illumina OmniExpress chip and 23andMe uses the new Infinium® Global Screening Array chip from Illumina. The fact that all of the chips come from the same company may be confusing, leading some to believe that all tests are created equal. This is not the case. The chip used to process DNA samples is only one part of the process. Each company develops their own analysis of the results, references different population samples and provides different reports. In addition, each one of these DNA test providers offers different tools for you to analyze the data you receive, creating variations in results, accessibility and usefulness.
For our evaluations, we assembled a group of testers willing to spit into a tube on camera. We chose four individuals of varying backgrounds. Two had previously taken one or more DNA ancestry tests, and two had not. Two had fairly well-documented family histories to compare against, one was adopted, and one had information about one side of the family, but not the other. All of us took DNA tests from AncestryDNA, 23andMe, National Geographic and Family Tree DNA. One tester also took each of the five additional tests we reviewed. 
DNA tests give you an educated estimate of your ethnic makeup and help inform genealogical research by verifying existing family trees and informing future avenues of investigation. Additionally, there's a possibility you'll find living DNA matches - distant cousins and other relations - who could share their family history with you to build a bigger picture of your family tree.

Of the 23 pairs of chromosomes in the human genome, 22 are autosomes. Most direct-to-consumer DNA tests look primarily at your autosomal DNA to determine your geographic ancestry percentages. This DNA is a mix of inherited DNA segments – half from each parent. Because everyone inherits at least one X chromosome from their mother, DNA tests often include the X chromosome in autosomal testing, though the X chromosome is not an autosome.
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?
Our testers received notifications that our samples were received 15 days after we mailed them. The email also said that it would take approximately six to eight weeks from that point for results. It actually only took 17 days after the email to get our results notifications. From mailing our samples back to collection, all in all, was 32 days. This was slower than several other DNA services, including the speedy MyHeritage DNA, which had a 16-day turnaround.
23andMe has also been the target of concerns over how they handle user data. Their tools are more advanced than what AncestryDNA offers, and the International Society of Genetic Genealogists claims that they have the most accurate admixture results – but many in their database are health testers and may not be receptive to matching for genealogy purposes. They also offer no family tree integration at all.
Finding small percentages of unexpected ethnicities may prove to be inaccurate upon further examination, and NOT finding traces of a certain group, such as Native American, may not necessarily prove that you do not have ancestors from that region or group. You can read more about that as it pertains to Native American research here. You can apply this statement to any ethnicity or region you might expect or hope to find in your results.

I’ve tested with each of the big five. It’s wise in the sense that you have access to every database of matches. Some companies allow you to upload your raw DNA that was generated from other testing companies. That can save you a lot of money. So you can test with Ancestry, then upload your raw DNA to MyHeritage, FTDNA and LivingDNA. 23andMe do not allow uploads right now so you’d have to test with them separately. Ancestry also does not allow uploads, that’s why I would use them to do your initial test.

the beauty of a y-DNA test is that it tracks the paternal y-chromosome…..yes, even indicating a surname change but not when the surname changed [does not match known male descendants]. In all DNA testing, it really helps to have researched about 5 generations back on all lineages……that way you can find common surnames in the autosomal tests. The y-DNA tests go back for centuries…..and the autosomal testing really only goes back about 5 generations…….

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.
I hope this helps to clear things up. Ancestry DNA testing is not an exact science, and is limited by the fact that we don't inherit the exact same DNA our parents had, meaning that with each new generation, old DNA is lost. Ancestry tests can provide estimations of our genetic ancestry, and though they are improving all the time, they can't tell the whole story of our heritage.
Ethnicity can be defined in many ways and by a wide range of factors. Culture, language, nationality and religion are just a few of the influences that can contribute to your sense of ethnic identity. DNA testing offers another way to help you define your ethnicity, by looking at your genetic ancestry. Even families that have lived in the same place for several generations may have a diverse genetic heritage, and if you were to trace your ancestry back several hundred thousand years, the current thinking is that you’d discover you share the same ancestral origins as all humans, in Sub-Saharan Africa.
The DNA profile is the ultimate in individual identification and offers a 'tamper-proof' means of identity. The profile need only be produced once and the DNA sample used to produce it can be stored as a permanent DNA record throughout the dog's life. Identification could be essential in a number of instances. For example, the availability of a profile could be used to identify an animal that may have been lost or stolen, and subsequently recovered. The profile could also be used to check the authenticity of a DNA sample being used to screen for the presence of disease-causing genes. Many such tests are being developed and it would be invaluable to be able to verify that the correct dog's DNA is being tested for the presence of the deleterious gene. Repeating the DNA profile on the same sample of DNA being used to carry out the gene test would be straightforward and prove conclusively that the correct animal is being tested.

Although the project states that most participants won’t receive any useful information, patients will be told if something is found in their genome that is relevant to the treatment, explanation or diagnosis of their condition. They can also choose to learn if they have a genetic risk factor for another disease, such as the BRCA1 gene mutation that can cause breast cancer. Genomics England will only look for risk factors that are linked to a disease that can be treated or prevented. Untreatable conditions, such as Alzheimer’s, are not looked for.

TTR-related hereditary amyloidosis is often managed by treating the symptoms through medications or surgical intervention. However, some recently approved medications work by decreasing the production of the TTR protein, which makes it less likely to build up in the body's tissues and organs. In addition, most of the TTR protein is produced in the liver, and liver transplants have been beneficial for some patients. Scientists are currently working on other treatment options for this condition.

The DNA test thing is a scam as the results cannot have precision. I know where my recent ancestors came from and wanted to “test a DNA test”. My ancestry is 3/4 Spanish Valencian and 1/4 Spanish Ibizean (Ibiza): I have family papers and village names for my recent ancestors: they all have typical Spanish/Catalan names and I expected this to be reflected in my results.

In addition to showing geographic ancestry percentages, some direct-to-consumer DNA tests also include insights about physical traits like hair and eye color. With 23andMe, this trait information is mostly available in the upgraded Ancestry + Health kit, but some interesting tidbits can be found in the Your DNA Family report, which is available if you opt to participate in the DNA Relatives service. 
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.
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.

Most companies will use algorithms to compare the genetic variants uniquely associated to a reference population with those identified in the person being tested. This can help them exclude unlikely population groups from your ethnic mix, and ensure that the ethnic groups you’re shown to be composed of are more accurately reported. Although most companies will share the reference populations they use with their customers, they rarely provide information on the algorithms they’ve developed.
23andMe tests autosomal and mitochondrial DNA for all users, as well as Y-DNA for males. These different types of DNA play into the service’s different ancestry reports. Your geographical ancestry report stems from the autosomal DNA, which is a combination of both of your parents’ DNA. Your maternal and paternal haplogroups are derived from mitochondrial DNA and Y-DNA respectively. These show the migration of your direct parental line through thousands of years. 23andMe also identifies your Neanderthal ancestry.
“My concern is that more and more of these tests are being put out, and people are being persuaded to have these tests done, and they get results back that are very often of very low value and dubious helpfulness,” she says. “And often people are told to go to see their GP and that then places a direct stress on the NHS, at no cost to the company. The companies make their profits and walk away, letting the NHS sort out all the fallout, the push-back, from the test results, in a way I find absurd. Why should the NHS have to prop up the problems that these companies create?”
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.
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