Pat, Both sons carry your father's Y-DNA; accordingly, unless the male line has been interupted, they will also have the same Y-DNA as your great grandfather. Unfortunately there is no way to connect back to your great grandfather other than a paper trail. Y-DNA testing will only show relationships between people who have been tested for their Y-DNA. One could get a Y-DNA sample of one's great grandfather if one knew where he was buried, but most people do not go this route unless the circumstances are extra-ordinary. Of course this means that Y-DNA can and is being used by 10's of thousands of people to find what I refer to as "Y-DNA Cousins". Now here is where the science meets statistics meets art. How close 2 or more Y-DNA Cousins are to each other when they have no known paper trail is a wee bit of a SWAG. For most people considering taking the Y-DNA test let me recommend strongly the 67-markers test. Why? Experience with my Johnstons in Poldean group has taught me that. Let's take a look at the various tests and what we can learn from them. 12-markers test: the most basic test being marketed; used by National Geographic in their human genome project in an attempt to explain the migration of mankind from his inception to today. If one is lucky, one will find out which major haplogroup one belongs to and little else - many do not though. 25-markers test: a waste of time and money, in my opinion. It adds little that is really useful to the 12-markers test. 37-markers test: this test helps in defining close relationships within the past few hundred years. For example, in our Johnstons in Poldean group we've been able to help 2 pairs of Cousins to get together and cooperatively work in finding their Most Recent Common Ancestor. Both pairs had a difference of only 1 mutation, but their MRCAs were from different generations, ie: one pair found their MRCA in the 1750's while the other pair found their MRCA in the 1850's. On the other hand one of our Cousins had 2 of his grandsons tested. Each differed by 1 mutation from his results, and each was at a different locus (marker). All of this illustrates the well-known fact that mutations occur randomly. We never know when they will happen or where. 67-markers test: in most cases, other than when 2 or more Cousins are known to be from the same family line, this is the test that should be taken. The loci, or markers, #38-67 are most useful in determining direct family lines. For a year or so in our Johnstons in Poldean group we relied primarily on the 37-markers tests, but when a handful of Cousins had their tests upgraded to 67 markers it became evident that the upgrade was invaluable as it indicated a close relationship between 2 Cousins who thought that they were from different family lines, and 2 other Cousins who thought they were from the same family line turned out to be from totally different lines. Now that we've had 33 of our Cousins upgrade to 67-markers we are "true believers" in getting the 67-markers test done first. I hope that this helps you a wee bit :-) Good hunting, Cliff. Johnston "May the best you've ever seen, Be the worst you'll ever see;" from A Scots Toast by Allan Ramsay ----- Original Message ----- From: "pat lewis" <carmodyp@bellsouth.net> To: <CountyCork-L@rootsweb.com> Sent: Monday, August 24, 2009 10:41 PM Subject: [CO CORK] DNA question >I have no living male members except my sons, Father died in 1966 , > brother in 1987........... Could either son have the DNA test and what > would it show, how could I make any connection to great grandfather who > died 1905 or any living relative that I know nothing about? > Check out the Ireland GenWeb County Cork Website at: > http://www.rootsweb.com/~irlcor/ > It is a good place to find information related to your family research. > ------------------------------- > To unsubscribe from the list, please send an email to > COUNTYCORK-request@rootsweb.com with the word 'unsubscribe' without the > quotes in the subject and the body of the message