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DNA Test LowdownWant the lowdown on DNA testing for genealogy?  Read on!


 DNA – the basics


Anyone who knows me will tell you that science was not my favourite subject in high school, so I am definitely not the expert on the science side of all this.  However, I do believe that to use DNA as a tool to find biological ancestry, a basic grounding is helpful.


We inherit DNA from our biological parents, who inherited it from their parents, who inherited it from their parents, and so on.  No one has the same DNA profile as you (even identical twins DNA is not completely identical although it mostly is).










DNA InfographicHumans are living beings, and all living beings are made up of cells.  Cells contain many things, including hereditary material.  For our purposes, this includes DNA and mitochondria.   DNA is organised into chromosomes.  We have twenty-two pairs of chromosomes known as ‘autosomes’; and another pair of chromosomes, which are the ‘sex’ chromosomes (so 46 chromosomes in total, one half of the pair inherited from your mother, and the other half from your father).


The sex chromosome is what makes us either biologically male or biologically female; females have two ‘X’ chromosomes, and males have one ‘X’, and one ‘Y’. 


Mitochondria cells convert energy from food for the cells to use to function and also contain mitochondrial DNA (aka mtDNA).  This form of DNA is passed to you from your biological mother.




The types of DNA test


For genealogy purposes, there are essentially three types of test, autosomal, Y-DNA, and mtDNA.  Although interesting, I don’t find Y-DNA and mtDNA particularly helpful for genealogy purposes, but it’s helpful to understand what the testing is and whether it might be useful for you.






Y-DNA looks at the Y chromosome of males.  As it is passed on from father to son only, a Y test will only give you information about a male’s direct paternal line, i.e., your father’s, father’s, father’s father etc.   If you wanted to know about your mother’s father’s line, you would need to test her father (or one of his brothers, or their male offspring, a male sibling of hers or his son). If there are no surviving males that fit into one of these categories, then no Y-test can be done.




Y-DNA testing is available through both FamilyTreeDNA and 23andMe, and testing with either company will give you what is called your ‘haplogroup’.  This is a group of people who share the same ancestral origins, and can usually give you a geographic origin of your direct paternal line (for example, my father’s haplogroup is within RP-312, which is common in Europe, and in particular the British Isles).  FamilyTreeDNA enables you to drill down further into your haplogroup with more extensive Y testing (the most expensive of which is its Big Y test at $649, which drills down into the most current possible level, and the haplogroup gets updated as they are further able to refine).


FamilyTreeDNA also has Y-DNA matches, so can be used to find those who share your paternal line, but the database size is far smaller than any autosomal database, so testing for this purpose alone can be a pretty expensive gamble.  For example, I tested my father’s DNA at the highest level, and his only Y matches are so remote as to not be identifiable, and likely the common ancestors are hundreds and hundreds of years back, probably before surnames existed. He doesn’t share autosomal DNA with any of his Y matches.  That’s not to say you shouldn’t Y test if you are interested in deep origins, but don’t test expecting to find answers to more recent ancestry.  It is possible, but autosomal testing is the cheaper way to go.




One thing that Y-DNA testing can do, is give adoptees and those with unknown fathers a clue as to possible birth surnames which you can then look for in your autosomal matches.  You can also use the haplogroup information at Gedmatch to see if any of your matches there have indicated belonging to the same haplogroup.






MitochondriamtDNA looks at the mitochondrial DNA inherited from your mother (note, this is NOT the same as X-DNA; see the next section for information about that), and both males and females can take an mtDNA test.  It works in an opposite way to Y-DNA in that it will give you genetic information from your direct maternal line only; i.e. your mother’s, mother’s, mother’s, mother and so on.  A lot of people take it for interest, as you find your maternal line haplogroup which, like its Y equivalent, will usually give you a geographic origin for your direct maternal line (for instance mine is U5b1d which is a branch of U5, one of the oldest haplogroups in Europe.


For more recent genealogy mtDNA is not really useful; partly because the only site you can currently see matches on is FamilyTreeDNA and the database is small, but also because mitochondrial DNA mutates more slowly than autosomal DNA so it doesn’t change much across generations.  In my own mtDNA matches shown on FamilyTreeDNA, I share no autosomal DNA with any of my matches, neither does my father with his.




Autosomal  (or atDNA)


Autosomal DNA is, to me, the holy grail of genealogy testing.  It helps you find out about your ethnicity and can help you find living relatives and finally break through longstanding brick walls.  Autosomal DNA testing is what has made it possible for countless people with unknown parentage, including adoptees and foundlings, to find biological relatives.  It’s currently a hot topic in the press since exactly the same processes and procedures used for unknown parentage cases is being used to identify suspects in criminal cases, and to identify unidentified murder victims and other John and Jane Doe cases.




The reason it’s so useful is because it’s a good indicator of more recent ethnicity since it’s passed down from generation to generation.  This means it’s possible to use it to find people who share DNA with you, which means you can then potentially identify the ancestor whom you both descend from.




How do we inherit DNA?




As we’ve covered above, you receive 50% of your DNA from each of your biological parents.  They, of course, inherited 50% of their DNA from their parents.  So you’d think that you must, therefore, have inherited 25% of your DNA from each of your grandparents, right?  Not quite!  The more accurate answer is you will have inherited approximately 25% from each of them, but it may be a bit more, a bit less.


Before the DNA passes to you, it does this thing called recombination, which basically means its all gets mixed up.  This is why siblings do not share the same DNA.  The same thing happens over and over again, so it is entirely possible to share no DNA with a fourth cousin, and very little (or again, even none) with a third cousin.   As a real-world example, I  share just 7.8 centimorgans of DNA with one of my known second cousins once removed, but my father (his second cousin) shares over 100cm with him.  I must have inherited very little DNA that comes from our common ancestors.




One more thing – what’s a centimorgan?  Simply put, it’s a unit of measurement for DNA.  It’s used by all the test companies except 23andme, who make things a bit simpler and just refer to the percentage of DNA you share with another person.




This is just a very high-level overview of the science, which I believe helps you understand further about which test or tests you might like to take, and so that you why the closeness of a match helps estimate the exact relationship you are likely to share.  Thankfully DNA Painters Shared cM Project Tool has taken much of the hard work in working this out.








Where do I get my DNA test? – the lowdown on the four major DNA testing companies (plus one more!)


There are currently four major DNA testing companies, Ancestry, FamilyTreeDNA, 23andMe, and My Heritage.  The companies differ in precisely what you get for your money, and how you test, but all feature tools to see your ethnicity results and matches to people sharing some aspect of your DNA, together with tools to work with those matches.  The test is simple, involving either a saliva sample or a cheek swab and full instructions are included with all test kits.  It does usually take several weeks to get your results through, which can be tough if you are at all impatient (like me!).




DNA tests companies compared


Test links:



As well as testing your autosomal DNA, your results sometimes include testing of your ‘X’ DNA as well.  If you are male and you see a strong match with someone else on your X chromosome, then you know that the match must be on your mother’s side, which can help narrow things down a lot, particularly if the match is also with a male. It gets complicated after that generation; it can be a bit of a headache to work out who DNA could have been inherited from, and also because X DNA doesn’t recombine in the same way as autosomal DNA, you can share a fair amount of X DNA with someone with whom you are not related within the last few generations.


To be honest other than looking out for any large matches, I’d concentrate on autosomal matches; a good rule of thumb is if you don’t share a fairly sizeable amount of autosomal DNA with a person you also share on the X with, you are unlikely to be able to work out who your shared ancestor is since it could be several hundred years in the past.


If you aren’t that concerned about the ability to find DNA matches or relatives, then I would go with any of the ‘big’ four, although I would suggest going with Ancestry or 23 and Me if you might eventually want to take advantage of other DNA sites ethnicity functions or DNA relatives databases, just because those are the only two who do not at this time accept uploads from other companies.  If you want a more in-depth analysis of your British ethnicity, I would go with Living DNA.


If you do want to take advantage of DNA matching/relatives databases, and/or your specific goal is to find biological relatives or just identify your biological roots, then I highly recommend testing at Ancestry first.  If that yields you no results, and you have a bit more cash to lay out you can maximise your chances of finding answers by doing the following:


  1. After testing at Ancestry
  2. Upload your DNA to FamilyTreeDNA
  3. Upload your DNA to Gedmatch
  4. Upload your DNA to MyHeritage (free until 1 Dec)
  5. Test at 23 and Me
  6. Optional – If you have British roots, test at Living DNA, which will shortly be opening up a match function.


Just for transparency’s sake, as indicated at the top of this post, although I am an affiliate of all the major DNA testing companies, this has no bearing on my recommendation.  I simply recommend this order because it’s the most cost-effective way to test and be found on multiple databasesI recommend Ancestry as a first test purely because it has the largest database, which is pretty important if you are searching for biological relatives.  At the current time, its database is more than double any of its competitors, and this remains true in 2020.




What about privacy concerns?


Be sure that you are happy with what you are signing up for with any of the test companies, but also be aware that you can opt out of the DNA matching part of any of the test companies should you wish to.  In terms of specific privacy concerns, the only one I would caution the use of at this time is Gedmatch if you have any concerns at all about its use by law enforcement to find criminal suspects, or its relative openness for anyone to use for identifying people.  However, it’s very easy to upload a sample to Gedmatch, make any data about the test donor anonymous, and use a throwaway Gmail address as the contact email, should you have any concerns.  The bottom line is, if you want to find relatives, these are the best scientific tools for the job.




Ethnicity results


As I’ve stated before, if you are just testing for interest in your ethnic breakdown, it doesn’t really matter which company you pick to test with.  I only recommend testing with one in fact, because no test will agree on your exact ethnic makeup, since they all interpret ethnicity differently.  To me, the non-scientist, they all seem broadly accurate at the very overview level (e.g. European / African etc.), and not necessarily accurate when you go down into detail (not least because they keep changing their minds and you will get semi-regular emails to check your ‘new’ breakdown).  To be honest, I would probably go with whoever was currently the cheapest and leave it at that, unless you’re particularly interested in British DNA, in which case go with LivingDNA.