Part I of this genetic DNA testing tutorial gives a brief overview of the types of DNA tests used for genealogy. If you are new to DNA testing, give this a thorough reading before purchasing ANY tests. Learn how these tests work and what they reveal. Think through WHICH ancestors you are researching, WHO to test and WHAT tests to do. Commit to paper an ideal DNA testing plan. If you are doing this for genealogy research, you'll want your test results match-enabled. This will pay HUGE dividends later. Like the genealogical paper trails you are creating, DNA tests lay more foundation stones for future research.
There are plenty of resources available in book form and online to turn to for assistance, particularly with your autosomal DNA results. Family Tree DNA (FTDNA), Ancestry DNA, 23AndMe, MyHeritage and Living DNA do autosomal DNA testing with matching.
Do not assume that if you transfer your results from one testing lab to another that you will get the full spectrum of matches with a transfer account that you would have if you had swabbed / spit. You may not.
Besides autosomal testing, also consider incorporating the maternal and paternal line tests into your research. Unlike the autosomal (universal lineage) test, which has a limited generational reach, the maternal and paternal line tests have a long multigenerational reach. They target specific lineages and reveal the distinct genetic signatures of patrilines and matrilines. Results from such tests should be as much a part of your research documentation as birth, marriage and death dates. Some paternal and maternal line haplogroups do cluster in certain places in Ireland. Those results may provide you clues to help you better target your geographic origins.
Paternal line testing at FTDNA is covered in parts III, IV, and V of the same online tutorial. FTDNA provides results details and tools not available at other labs.
Only Family Tree DNA does full matching on paternal and maternal line results in addition to autosomal matching. [At the risk of sounding like a salesman for FTDNA, I will inject here that I do not gain monetarily from the sale of any DNA tests.] When you do multiple types of DNA tests in the same account at FTDNA, you can run Advanced Matching. For example, you can run a scan to see who matches you on both mitochondrial AND autosomal DNA. If you want full 100% matching on multiple types of tests and the ability to run Advanced Matching on those tests then FTDNA is a good place to do that.
Finding willing and able relatives who can represent the matrilines and patrilines you are researching can be difficult to impossible. Why? Your relatives might not be comfortable doing DNA testing. But assuming they overcome their reticence, there are other problems. It can be astonishingly difficult to find an eligible relative who is a suitable proxy for a particular lineage. Male lineages regularly go extinct due to priests, bachelors and only daughters. Female lineages regularly go extinct due to nuns, spinsters, and only sons. We then fall back on the autosomal test since we are unable to find a suitable relative who captures the genetics of the specific lineage we want to study. So if you are fortunate enough to have a willing and able relative suitable for a matriline or patriline test, do not delay taking advantage of that rare gift. Get that relative fully tested pronto. Relatives DO pass away!
DNA Testing is not a substitute for conventional genealogy research. You need both. In fact, the two seem to work both WITH each other and AGAINST each other. Without familiarity with and awareness of the rigorous proof standards that genealogy research entails, it is all too easy to assume that the hints for your family history that you might see at record websites are accurate. Or, you might assume that what you see in a match's family tree is accurate. Moreover, as with genealogical record evidence, people often jump to unwarranted conclusions on the slimmest of DNA evidence. For example, a man might assume he has no surviving male relatives with his surname because he does not have surname matches in his patriline test results. The truth may be that he has not done enough research to locate distant relatives sharing a same direct paternal line ancestor, or maybe those relatives have not tested. Autosomal DNA also has its difficulties. The probability of matching a known relative starts to fall substantially after the second cousin relationship. The chances of matching get very slim when you have known 5th or 6th cousins do an autosomal test. Failure to match may make you question your otherwise solid genealogy research.
This is why, with autosomal tests, the recommendation is to test as many relatives in the oldest living generations of your family as possible. With patriline and matriline tests, extra testing is not usually necessary, unless your research has turned up a fellow researcher and the two of you suspect you share a common direct paternal or maternal ancestor. Then, a pertinent lineage test applied to the right person can certainly help verify your research.
There is another difficulty with autosomal DNA. Earlier it was mentioned that in FTDNA, you can run a utility to see if your DNA relatives match you across multiple tests. If there is such a person, you may need to establish that you are related to that person in one way. If you have many generations from ancestry from a rural or isolated community, chances are that you could be related to that match in multiple ways. The multiple relationships can be enormously difficult to tease out.
The Cork Ireland DNA Project at FTDNA is administered by Ann Marie Coghlan, a professional genealogist who is active in the Cork Genealogical Society. Read the FAQ for instructions on how to participate with your autosomal DNA.
The project runs an ongoing study of mitochondrial DNA lineages believed to have come out of County Cork. Occasionally, statistics are graphed on paternal haplogroups of County Cork origin. This website maintains those results for the project.
Surname projects are normally hosted at FTDNA, and normally require at least a Y DNA test taken by a man whose last name is a project surname. Check with the individual projects to see if they admit other types of tests. More resources for the major surnames of Cork are accessible under Surnames.