This article first appeared in the St. Louis Beacon, March 4, 2009 - St. Patrick's Day is coming up in less than two weeks, and I find my thoughts turning to matters Irish. Today I would like to focus on Irish genes. As you will see, modern DNA biology has a lot to say about them.
Our human genes, Irish and otherwise, are surprisingly changeable, their messages written in our DNA in sequences of nucleotides that changes much more frequently than most of us imagine. Why?
As Forrest Gump might say, "Things happen": Errors occur when our DNA is being copied to make our children; gene damage occurs when chemicals like those in cigarette smoke damage DNA; random DNA changes miss being corrected by the cell's error-detecting machinery.
We humans have, over the centuries, accumulated lots of changes in our DNA, changes scientists call mutations. "Our DNA is a history book," geneticists say.
With the molecular tools that modern genetics provides, scientists are beginning to read that book, to trace the course of our species' history by tracking the changes that have accumulated in our DNA. The National Geographic Society, for example, has begun a Geno-graphic Project comparing more than 100,000 DNA samples from people all over the world, from Arctic Inuit Eskimos and Kenya's Masai to Australian aborigines and North American Pueblo Indians. Their hope is to create a picture of ancestral migratory routes, the historical paths people have taken as they populated the globe.
To gain the clearest possible picture of the past, gene researchers focus on DNA of the Y chromosome and the mitochondria. As readers of my work will recall from earlier columns, the Y chromosome of human males does not recombine with other chromosomes. This has the effect of keeping mutations together once they occur. Similarly, the mitochondrial DNA of females is passed down from mother to child without recombination (sperm contribute no mitochondria to the fertilized egg).
To compare large numbers of DNA samples, it is not practical to sequence the entire Y chromosome or mitochondrial DNA of each individual. Instead, investigators monitor several dozen highly variable DNA locations, short bits of the chromosome within which lots of mutations have occurred.
Because DNA mutations are rare events and there has been no recombination to shuffle the changes, when the same particular combination of mutations (what gene researchers call a haplotype) occurs in two people, they almost certainly are related, having inherited their Y chromosome or mitochondrial DNA from a common ancestor. Looking at lots of individuals in this way, investigators can build up a picture of who is related to whom -- a portrait of the past, inscribed on our genes.
And this leads us to the Irish. To see how, consider a study carried out in 2006 by Daniel Bradley and colleagues at Trinity College in Dublin, Ireland. They set out to apply DNA studies to Irish history, which has always been a bit of a muddle. Writing did not become common in Ireland until 600 AD, and little is known for sure of earlier events in Irish history. This has not, of course, prevented the Irish from preserving a rich story of those times.
Much as the British tell of a mythical King Arthur who few historians believe was a real person, so the Irish recount the tale of an Irish high king of the fifth century A.D. from whom an alarming number of Irishmen claim descent. Niall Noigiallach -- Niall of the nine hostages -- was so named because early in his reign he consolidated his power by taking hostages from the royal families of each of the five provinces that then constituted Ireland, as well as from Scotland, the Saxons, the Britons and the Franks.
He founded a dynasty, the Ui Neill ("the descendants of Niall"), which ruled the northwest of Ireland from about 600 to 900 A.D. When the Irish took surnames around A.D. 1000, some chose names associated with the Ui Naill dynasties, names like Gallagher, Boyle, Doherty, O'Conner, Reilly, Flynn, Devlin, Donnelly, McLoughlin, Molloy, O'Rourke and of course O'Neill (The prefix "O" is often added).
Did Naill of the nine hostages really exist? The DNA evidence gathered by Bradley argues "yes."
About 20 percent of men in northwest Ireland have a distinctive genetic signature on their Y chromosomes, a haplotype (that is, combination of mutations) carried down for more than a thousand years. This signature haplotype predominates in the northwest, the seat of Ui Neill power.
Indeed, wherever in the world you look (the Irish were particularly adept at migrating -- more than 400,000 residents of New York City claim Irish ancestry), this haplotype is much more common among Irishmen with the Ui Neill surnames than among Irishmen as a whole.
Niall is said to have had 14 sons, a large number even for those days, which might go a long way toward explaining that about 2 million men worldwide now carry his distinctive Y chromosome. Like Genghis Khan, ancestor of 16 million men in Asia, Niall of the nine hostages seems to have left quite a genetic footprint.
George B. Johnson's "On Science" column looks at scientific issues and explains them in an accessible manner.
Johnson, Ph.D., professor emeritus of Biology at Washington University, has taught biology and genetics to undergraduates for more than 30 years. Also professor of genetics at Washington University’s School of Medicine, Johnson is a student of population genetics and evolution, renowned for his pioneering studies of genetic variability. He has authored more than 50 scientific publications and seven texts.
As the founding director of The Living World, the education center at the St Louis Zoo, from 1987 to 1990, he was responsible for developing innovative high-tech exhibits and new educational programs.
Copyright George Johnson