Some of you may recall my previous ambivalence about DNA testing. Having entered the pool, so to speak, I am changing my tune. “Come on in, the water’s fine!”
As we see from the genealogies of small early communities of emigrated groups into areas outside of Ireland, Irish families frequently became intertwined through marriages among their neighbors. We may forget to consider that this would likely have been very much so in the Old Sod. There is a strong probability that families in the seventeenth through nineteenth century Irish townlands had been related in various ways to other surnames in their area and in neighboring counties. Not only would they meet in the dailiness of their lives, but their reach to other communities would extend when they attended festivals, fairs, and other popular religious and social events. Groupings in Griffiths Valuations and other “census substitutes” should perhaps not simply be looked upon as names of random neighbors mixed among particular surnames, but, instead, as potential clusters of inter-related families.
In scholarly genealogical research we seek paper trails that evidence linear tracks through the generations, and try to find as many supporting details as possible. Making the leap to another country and landing in the correct physical location might be a very long shot without specifics that factually anchor an ancestor there. With so many given names repeated throughout the generations, searches often turn up too many possible needles in a given haystack. Honing into a county is important, but until one finds the specific neighborhood within a specific town, s/he may forever only feel “warm”.
When documents are missing and it seems impossible to bridge one continent to another, DNA testing may help to close, or at least narrow, the gap. I now realize that DNA testing can actually help to clarify a hunch, and I believe that it has the potential for allowing one to be able to eventually prove a location beyond a reasonable doubt. One can then focus upon specific needles in the haystack—while retaining one’s awareness of the other nearby needles, but not allowing them to steer one entirely away to unrelated tangents.
Lyn-David McMullen (Laighin Daithi Mac Maolain), the surname administrator for the Mullen-McMullen DNA group, has recently been incredibly helpful to me in generously explaining basics about the DNA tests. With his permission I will attempt to share some of that here. Although it seems unlikely that any of us would be able to find and/or track them all genealogically, by our sixth generation back, as our two parents became multiplied by two more each, etcetera, we all ended up with 128 ancestors! Three types of tests may shed light upon a few more of them than our paper trails have led us.
Through the DNA tests we may be able to establish relative connections by comparing common segments in individuals’ DNA test results, and to learn whether a connection is through a male or female line. Some people may share one common male or female ancestor, but fall under different branches of descent (as we also find in our traditional research).
The Y-DNA test tracks the male “agnatic” line, through the “Y” sex chromosome. Others who match will share the male surname, or derivations of it. How close or distant a relationship is depends upon the number of identical markers in the Y-DNA string, particularly at the slow-moving, more stable, ones. These shared markers determine the “TMRCA (time to most recent ancestor)”. An introductory Y-DNA 12-marker test will begin to “open the door”, but to truly find connections with other males it is necessary to test a greater number of SNP (Single Nucleotide Polymorphism) segments. SNPs pertain to deep ancestral origins going back thousands of years. Markers are also compared for the more recent family relationships among those who share identical SNPs. Mr. McMullen wrote, “For our closest relations, we usually match perfectly on the first 25 markers.” For those starting out, the 67-marker test would be more useful, as it will provide deeper information beyond the basic ethnic ancestry. Mr. McMullen said that the 66th marker (DYS492) is a particularly important one to compare. At this point there occurs a branching of SNPs, going either to a P312 or U106 branch. (The marker number for P312 is 12, and for U106 is 13.)
For both men and women it is possible to take two other types of tests, which are broader and farther reaching than that of a surname line. These are autosomal (atDNA) and mitochondrial (mtDNA, the female “X” sex chromosome), which look for common female ancestors. Cousins, as might be presumed, have decreasingly less DNA match material the farther away they are from a direct line.
Autosomal results might produce different matches, even between siblings. Different companies produce different match results due to their particular sets of people tested. Differences can also be attributed to the fact that siblings get different combinations of gene-containing DNA chromosomes from each parent. The levels are retained for different lengths of time and become progressively weaker over generations. In order for people to be considered IBD (Identical by Descent) the largest chromosome segment/s that match must be at least 5.5 cM long and have 500 or more matching SNPs on that segment. If two people are in the same direct line, they are called “Common Matches”. Having family members take different tests might be helpful in gathering a range of DNA information that would be genetically shared among them.
Dr. Maurice Gleeson, an expert on autosomal DNA research, offers several online explanations and is a frequent speaker on the subject. He explained that one’s first cousins share common grandparents; second cousins share common great grandparents; third cousins share common 2nd great grandparents (gg); fourth cousins share common 3rd great grandparents (ggg); fifth cousins share common 4th great grandparents (gggg) and sixth cousins share common 5th great grandparents (ggggg). Another of his pages contains excellent illustrations that accompany his explanations about how DNA is contributed through the female and male sides of one’s ancestry.
He explained that autosomal tests look for matches among each person’s 22 pairs of chromosomes that exist beyond our sex chromosomes. These are written as “cM”, centiMorgans, and include the mixtures of lines created through married combinations. The autosomal test looks for a common ancestor back in time to about the 4th great grandparents. It reveals regional connections and both male and female cousins, determining how relatively close or distant in ancestry they might be to the one being tested. According to Dr. Gleeson, “the autosomal DNA test will detect 99% of your first and second cousins, 90% of your third cousins…but only 50% of your fourth cousins, and a mere 10% of your fifth cousins.”
According to Mr. McMullen, the “Family Finder” portion of the Family Tree DNA testing program tests the X chromosome, which is passed on by a mother. “A male can only get his X from his mother, thus eliminating his father’s entire half as the source for anything that shows up on his X…The man’s mother has two X copies, one of which came primarily from her mother and, one from her father, but they can be partially mixed. The copy that came from her mother’s mother, could be either from her mother, or her father’s mother, while the one that came from the mother’s father can only have come from his mother.” Given this information it seems especially important to look fully at lines on both sides of one’s ancestry, as threads between both sides may have mixed in any number of ways into the present.
DNA particulars are further explained by scientist Roberta Estes on her blog, DNAeXplained – Genetic Genealogy, where she also discussed the concept of haplogroups, “ancestral clans”. If a mutation is discovered in a line, a new haplogroup forms, and all descendants from that point forward will carry that mutation in their DNA. Links on her site lead to other informative postings she has made and questions she has answered for others.
There are offerings of free DNA tests for people of certain surnames for which administrators would like to build larger groups. This includes the Meagher/Maher surname group that wishes to focus upon those individuals who moved away to other places beyond the common ancient ancestral region in northeast Tipperary (which would be most of the Mahers, having been widely dispersed after the invasion of Oliver Cromwell in 1649-50). They have “particular interest in lineages that immigrated to Australia or New Zealand prior to 1930, or that trace to Cos. Galway, Clare, Limerick, Kerry, or Cork, with no known connection to Co. Tipperary.”
Although I have so much more to learn, our DNA clues have already provided me a means to fine tune my research on both sides of the pond, for which I am very grateful. I will probably always want to learn more, but heartily agree with Roberta Estes, who wrote, “Even if you do nothing more, it’s fun to identify your clan. It’s the only way of extending our genealogy back in time beyond surnames.”
©2014 Janet Maher / Sinéad Ni Mheachair
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