Lets suppose, as we have in the Sinnott/Sennett one name study, we have a whole lot of families who all believe their common ancestor came from Co Wexford, but the paper trail for conventional genealogy research has dwindled away, or we suspect that John and James who emigrated to the US about the same time were brothers but there is no documentation to prove it – genealogical DNA studies can now be used to show whether its possible that two families (that are at the moment quite separate on paper) are actually related and have a common ancestor. And no, we don’t have to go digging up g-g-g-g-grandfather John to get his DNA – remember, he passed it on to his son, and his son’s son, and so on to the present day. So we find a living male descendant and they get their Y-DNA analysed. That gives us a pretty good indication of the genetic signature for the whole family tree (well, the male side, anyway). If we want to check it, we find a distant cousin of the first person who tested and get their DNA analysed. If its a very close match, then bingo – we know the Y-DNA genetic signature (and whats known as a haplogroup) for our whole family group.

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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.
DNA profiling isn’t exclusive to human DNA. Animals also have genetic markers in their DNA which can be used to build up a profile for DNA identification or determining parentage. The most common animals that this is used for are dogs. Similarly to human DNA profiling, dog DNA profiling uses 10-20 markers in order to build up a profile that can be used to identify your dog if it is ever lost or there is some kind of ownership dispute. Companies that offer this service will often include the profile in the form of a certificate, with details about your dog along with its DNA profile. It should also be said that these companies tend to store your dog’s profile in their database, so you that you can check back with them if you ever need to.
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.
Living DNA offers the best biogeographical ancestry analysis on the market for people with British ancestry and they are the only company to offer regional breakdowns. With the inclusion of Y-DNA and mtDNA haplogroup information, this is a good all-round test for someone who wants an overview of their genetic ancestry. The test cannot currently be used for genealogical matching, though an autosomal matching service is promised for the future. As a late entrant to the market, Living DNA will start with a smaller database though the test is more likely to appeal to people in the UK, especially those who feel safer keeping their DNA data in Europe.
You might want to stay away from DNA tests if you or any of your close relatives have committed a crime. Although ancestry DNA testing companies don’t typically share database information with law enforcement, consumer DNA tests may result in future identification. For example, FamilyTreeDNA, which has a database of close to a million samples, has agreed to give the FBI limited access to the company's DNA database. This access consists mainly of consumer-level insights, like matches with other members of the FamilyTreeDNA community who have enabled family matching; by law, however, more in-depth investigation requires a subpoena.

— Once you have chosen a test and received your autosomal results there is still a great deal more fun to be had. Independent tools and websites created by scientists and enthusiasts allow you to take the raw data provided from FTDNA, 23andMe and Ancestry DNA and explore them in astounding detail–giving you a wide variety of new admixtures, phasing options, chromosome browsers, SNP tools and connections with family across the world. Gedmatch is our favorite because they have so many wonderful and meticulously updated tools from a variety of sources. Easily upload your raw data and run your results for free (if you love the tools, don’t forget to donate and uncover even more options.)