County Cork, Munster and Ireland DNA Projects
Admixture (Autosomal) Tests
An autosomal DNA test such as Family Finder is probably the most useful genetic test for finding relatively close kinship to people. It can greatly help adoptees find relatively close kin.
A-DNA tests your 22 autosomal (non-sex) chromosomes. Because these chromosomes recombine with each successive generation, thus getting diluted, the optimal situation would be to test your parents or grandparents and their siblings, if at all possible. Choose a person in the oldest available generation for the line you are researching. A practical limit in terms of how far the test can reach back is maybe 200 - 250 years.
Two test takers who share a common set of great-great-grandparents (i.e., are third cousins) stand a better than 90% chance of being an aDNA match.
Y-DNA projects trace direct patrilineal lines. Ususually they are surname studies, with each project tracing a particular surname and its variants and agnomens, but some Y-DNA projects look at geographic regions or several clans with documented histories, known to have inhabited certain territories. Y-DNA project goals often involve confirming or refuting what documented history tells us.
A Y-DNA test taker who matches 10 out of 10 markers with another tester likely shares common ancestry within about 72 generations, which is not very practical for finding relatively recent cousins. (At three generations per century, the common ancestor would have lived about 2400 years ago.) On the other hand, if the two testers match 111 out of 111 markers, they probably share a set of grandparents back within about six generations.
Nigel McCarthy's P314.2 (updated 5-Mar-2013)
Mitochondrial (mtDNA) Tests
One cannot normally trace surnames with a mtDNA project since women took their husbands' names and normally moved to their husband's locations. The Ireland mtDNA test collects all the mtDNA types that have appeared in participants with direct matrilineal Irish ancestry.
Because mtDNA changes so rarely over the course of thousands of years, and women historically moved to their spouses' locations, trying to find recent cousins is not normally a practical application of the mtDNA test. Unlike the Y-DNA test, which allows you to target relatively recent ancestry by testing more markers, mtDNA does not change frequently enough to find cousins with relatively recent shared ancestry, even when one tests the Full Genomic Sequence (FGS).
However, situations do arise in which through conventional genealogy research two people might discover they share a relatively recent common direct maternal ancestor. In that case, those two people should be able to validate their research by taking the mtDNA test and confirming that they match.
Considerable patience may be needed on your part to see fruitful matches after you take your tests. It took me well over three years to get just one match on the full genomic sequence (FGS) of mtDNA and even so, our common maternal ancestry could be as much as 16 generations ago - way too far to be able to trace. After more than two years, there is only one Family Finder match in which the two of us have a very good idea on how we are connected, and a few other matches that have ancestry from the same geographic regions but without a clear idea on the path to the common ancestry.