My family had always presumed that we were solidly British. My mother, our resident genealogist, has painstakingly traced five generations on her side back to Leeds and West Yorkshire, while my father’s clan hails from Bethnal Green in east London.

A simple swab of DNA, however, has changed everything.

In the space of a week I have accumulated no fewer than 43 new relatives, including a Mongolian, a Brazilian, a Hawaiian and a Kiwi. I have found that I share my “ancestral mother”, a woman based in the Mediterranean region more than 17,000 years ago, with the Russian tsar Nicholas II, the American outlaw Jesse James and, more prosaically, the television presenters Judy Finnigan and Anthea Turner.

This expanded family tree is the work of a website, GeneTree.com, launched last week. James LeVoy Sorenson, an American billionaire, has spent £60m developing it and promises to use DNA not just to help people to find new relatives, but also to bring them together with a Facebook-style interface that will enable them to share videos, pictures and family trees.

It has the potential to be big business. The internet has already fuelled an unprecedented boom in genealogy, allowing people to retrieve family records that were previously locked away.

Genealogy websites are now the second most commonly visited on the internet after pornography, with the biggest, Ancestry.com, attracting 4m visitors a month. When British census data from 1901 was put online in 2002, the website crashed under the weight of up to 30m hits a day.

DNA is seen as the future of genealogy. Its evidence is indisputable which makes it invaluable compared with written records, which are both limited and prone to human error, whether mistaken or deliberate. Put simply: one cannot mislay or misspell one's DNA.

For a fee of £73, GeneTree will analyse a mouth swab and compare it with the 100,000 DNA samples and 6m ancestral records on its database.

Researchers isolate a tiny percentage of human DNA known as mitochondrial DNA (mDNA) which unlike most of our genes remains almost unchanged from generation to generation as it is passed down from mother to child.

This extraordinary property means that everyone on earth carries a piece of information passed on directly from a maternal ancestor, “Mitochondrial Eve”, who is believed to have lived in Africa between 100,000 and 200,000 years ago.

Sorenson’s genealogists then feed the mDNA code into their database, producing both a “deep ancestry” that details an individual’s ancient origins and a list of those on the database with the same DNA sequence. These are relatives whose family trees meet usually within 20 generations.

“DNA is a revelation,” said Dr Scott Woodward, chief scientific officer at the Sorenson Foundation. “Written records generally go back just a few hundred years, and are subject to inaccuracies and human error. Mitochondrial DNA, on the other hand, remains almost unchanged over hundreds of thousands of years.

“Suddenly, people are able to find and communicate with relatives they never knew they had from all over the world, and discover their deep ancestral roots.”

While it is intriguing to find one has relatives spread around the globe, the spread of DNA genealogy has more serious implications. If I am related to a young man in Mongolia, what does that mean for traditional notions of race and national identity?

And, on a more practical level, how can I guarantee that my DNA profile will be protected by the databases that hold it?

PROFESSOR Bryan Sykes, chairman of Oxford Ancestors, a pioneer of DNA-based genealogy, believes his research proves that notions of race and ethnicity are merely constructs. Sykes spent five years analysing the DNA samples from 10,000 volunteers to produce a map of our genetic roots. He discovered that the Celts, Britain’s indigenous people, are in fact descended from a tribe of Iberian fishermen.

“We are not a race at all. We’ve been mongrels for 10,000 years and it has done us a lot of good,” he said. “You find exactly the same DNA fingerprint in what you otherwise consider to be different ethnic groups. It shows those ethnic groups are relatively recent ethnic constructs. The history of our species is one of movement, mixing and flux. There is no such thing as a genetically pure race.”

Last year his firm discovered that two white British women had the DNA signature characteristic of native Americans.

Doreen Isherwood, 64, from Putney, London, and Anne Hall, 53, of Huddersfield, are thought to be the direct descendants of native Americans brought to Britain as slaves. “I was thrilled to bits. It was a very pleasant surprise,” said Hall. “To have native American blood is very exotic.”

Studying mDNA has enabled genealogists to produce a map of the world’s ancestral roots. By comparing mutations in the mDNA, it is possible to identify clusters of present-day people with similar sets of mutations, which can then be traced back to 16 maternal ancestors worldwide.

According to GeneTree, my DNA falls into the category T2/T*, which means my maternal ancestor was based in the Mediterranean region about 17,000 years ago. Today, the DNA type is most common throughout the southwest corner of Europe and the eastern fringes of Asia.

Sykes takes a more romantic approach. In 2004 he published a ground-breaking book, The Seven Daughters of Eve, which was based on the theory that almost every person in Europe today can trace their ancestry back to just seven women. Rather than use scientific terms, Sykes gave the women names such as Helena, Ursula, and Tara. He identifies my maternal ancestor as Tara, a hunter-gatherer who lived 17,000 years ago in the northwest of Italy among the hills of Tuscany and along the estuary of the river Arno.

“It’s a very profound thought that the DNA in your cells has come from a long line of ancestors and ultimately one woman based in Tuscany,” he said. “It’s quite a wondrous thing. I’ve been doing it for a long time and I still find it an incredibly powerful thought.” BUT while undeniably powerful, it remains questionable how relevant “deep ancestry” is to human identity in the 21st century. I share the Tara clan, for example, with just under 10% of modern Europeans.

Of far more relevance to the family tree are the extensive DNA databases held by genealogy companies, which enable users to discover previously unknown relatives by comparing DNA fingerprints.

Oxford Ancestors offers a DNA test on the Y-chromosome, which is passed from father to son, for £150, which is then cross-referenced with its database of 10,000 people. People can then use the website to try to contact those who are exact matches to see if they will share family trees.

GeneTree is trying to take the process a step further. Users are given the age and location of any mDNA matches, and can then apply to become online “friends”.

“We are trying to make the site a social hub for families and friends, where they can share not just their family trees but pretty much anything they want,” Woodward said.

The databases, however, are not without controversy. While Oxford Ancestors destroys all DNA samples, GeneTree keeps them “indefinitely” unless otherwise instructed by users.

Privacy International, the human rights group, fears that the police or medical insurers could use court orders to seize DNA samples. It is particularly concerned that the Mormon church will attempt to gain access to the database. Sorenson is a prominent Mormon, and the church places a religious duty on its members to search out their family trees.

As a result, the Mormons hold some of the biggest genealogy databases in the world, with more than 4,000 family history centres in 88 countries.

The British information commissioner yesterday confirmed that he was investigating a similar complaint made by Privacy International about a tie-in between another Sorenson business and the website Ancestry.com.

GeneTree insists, however, that DNA results are not shared with any third party. While it admits it would be powerless to prevent data from being seized under a court order, it adds that the quality of the samples is not good enough to identify an individual on their own.

Others, however, are keen to see the techniques used in DNA-based genealogy applied to fighting crime. Sykes wants the government to implement a trial scheme where police could take DNA from a crime scene and cross-reference it with a national database of Y-chromosomes from men with known surnames.

He believes about 70 rapes and murders in Britain could be solved every year this way. He said: “I always think: how much quicker would the Yorkshire ripper have been caught if they had known that his surname was Sutcliffe?”

MEANWHILE, DNA-based websites remain invaluable to genealogists. In November 2005 a 15-year-old boy in America used a site called FamilyTreeDNA to track down his sperm donor father. The boy sent a swab to the company which added details to its database.

Nine months later he was contacted by two different men who matched his DNA, neither of whom knew him but shared a similar surname. By combining their surname with his father’s date and place of birth, which were supplied by his mother, the boy was able to track down and eventually meet his biological father.

In my case, despite asking several of my newfound GeneTree relatives to be my friend, they have so far steadfastly refused. I suppose no family gathering goes off entirely without a hitch.

Databases that can make a difference

The National DNA database

The Home Office-run national DNA database is the biggest in the world. It holds the profiles of more than 3.5m people, or nearly 5% of the UK population, and contains samples from suspects arrested for any imprisonable offence, even if they are not charged or are acquitted. It also contains the DNA profiles of 150,000 children

Icelandic DNA database

Icelanders’ genes have remained almost unchanged since Viking days, while a meticulous approach to family trees means some stretch back more than 1,000 years. The combination proved irresistible to deCODE, a pharmaceutical company that aims to marry DNA analysis with family histories and health records to develop new treatments for cancer and heart problems. To date it has medical and DNA information from 100,000 volunteers

National Geographic

National Geographic magazine and IBM started collecting cheek-swab samples from 100,000 volunteers around the world in April 2005. They hope data from the project will make it possible to map world migratory patterns over the past 150,000 years

Google

Google recently bought a £2m stake in a company called 23andme, which launches later this year. It will allow individuals to have their DNA read and stored, so that when medical advances relevant to them are achieved they can be notified

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