How is it possible to retrace the steps of our ancestors by analysing the DNA of living people? Inheritance is the key. Each of us inherits around six billion letters of DNA from our parents, three billion from each. Made up from four biochemicals; adenine, cytosine, guanine and thymine, our genes are read by scientists like very long strings of letters, sequences of A, C, G and T.
There are two special sorts of DNA that are particularly useful for learning about our past. Our fathers pass on Y chromosome DNA to their sons while mothers pass on mitochondrial DNA, or mtDNA, to their sons and to their daughters. But mtDNA dies with men and it survives only in the female line. This means we can read two stories in men’s DNA, one for their Y chromosome lineage and one for their mtDNA lineage. In women we can read only their mtDNA story.
It is important to realise that the Y chromosome and mtDNA are only a small part of our DNA, our genome. Nevertheless they are the most informative means we have for learning about our ancient lineages. However these two pieces of DNA are only a part of a much larger genetic inheritance that includes, for example, physical traits such as eye and hair colour or stature.
Scientists noticed occasional tiny errors of copying as our six billion letters were passed on down the generations. Known as markers, they were found to originate in particular parts of the world and through a technique called the molecular clock, they could be dated. . New markers are being discovered all the time, some of which arose rather recently, and can be specific to a particular surname or very concentrated in one place.
Once a marker has been discovered the next stage is to try to understand what it means. First we work out how it relates to other markers and place it on a phylogenetic tree – similar to a family tree but stretching much deeper into the past, with shared markers revealing who is related, rather than birth certificates. We then study where it is found, estimate how old it is, and infer as best we can, where it originated and dispersed to. Our R&D programme is therefore screening new markers we have discovered as well as those found in the 1000 Genomes project in a large sample of continental Europeans as well as British and Irish people.
By having your DNA tested we can inform you of the markers you carry and what we think they mean. Further to this, our historians will expand on the science to create a holistic understanding of your ancestors’ lives in the deep past.
Interpreting Markers, Making History
At IrelandsDNA we combine science with history to create the full picture of your past. Genetics, phylogeography, archaeology and historical analysis, along with an understanding of human behaviour and response to major historical events are pulled together for the first time… Here is an example of how DNA analysis can shed light on the deep past.
In a glacier high in the Alps near the border between Italy and Austria, a mummy was found perfectly preserved in the ice. In September 1991 two German tourists, Erika and Helmut Simon, at first thought they had found a modern corpse. Eventually nicknamed Ötzi, the body was, in fact, dated to around 3,300BC. Amazingly, much of the man's clothing and equipment had survived intact for more than 5,000 years. He had been killed in a violent manner, probably by a blow to the head, and his forearm was freeze-framed in a protective position across his neck and face. Very soon after he was left for dead, and the ice buried him.
In 2011 scientists were able to sequence Ötzi's whole genome and the results were published in 2012. They offered fascinating insights. His Y chromosome was found to be in the G group of lineages, but very surprisingly, he shared his Y chromosome DNA with what has been extracted from 26 other ancient skeletons. These men were all farmers, amongst the earliest to bring farming techniques to Europe. This was the greatest revolution in human history but – because of its great antiquity – its spread and origins are not well understood. Men with Ötzi's G group DNA appear to have been incomers, men who brought the new way of life and its techniques into Europe. They appear to have taken native women for partners and what their DNA shows is that the introduction of farming was an event as well as a process. New people brought new knowledge about how to feed ourselves; how to plant, tend and harvest crops, how to domesticate and manage animals and how to change the landscape to accommodate a different way of living.
Ötzi's DNA appears to have come from close to where he died. A comparison with 1,300 contemporary Europeans indicated close genetic affinities with Southern Europeans and in particular, the inhabitants of the Tyrrhenian islands of Corsica and Sardinia. Reaching across millennia, DNA can show how the mummy found in the ice and the first farmers to cultivate crops and milk animals in Europe have modern descendants, some of whom have been found in Ireland.
Many waves of immigration followed the end of the last ice age and the introduction of farming, right up to recent times. Consequently Ireland is now a nation of men and women of tremendously diverse origins. This richness can be measured by DNA testing and, by using an aggregate of many individual stories, a genetic map of Ireland can at last be drawn. And finally, with your help, two central questions can be answered; where do we all come from and who are we?