Knave Hill, Leicestershire
First screened 24 February 2008

DNA and human ancestry

Phil Harding had his DNA tested to try to trace his ancestry as part of the Knave Hill programme. So what is DNA and how can it be used to enhance our knowledge of where different peoples came from?

DNA: what is it?
As with any Airfix modelling kit, you need a set of instructions if you are going to build something – and the more complicated the thing you're going to build, the more complicated the instructions.

DNA, or deoxyribonucleic acid, is like a colossal step-by-step genetic guide effectively 'saved' in a biological form. To put it simply; it holds information on what cells should do. When growth and development start on their journey it's the DNA that holds the map and gives the directions. The detail on the DNA 'map' is held not on pages, but within genes.

Every living thing carries DNA within its cells. Physically it's made up of a heady mix of phosphates and sugars, but it's the actual molecule structure that holds the key. The components are held together in the famous spiral strand 'double-helix', packaged up in a neat device called a chromosome. These can replicate themselves and are passed on from generation to generation – which is what makes it possible to trace human ancestry through DNA.

Genetic inheritance
We each inherit our DNA from our parents. Most of it gets mixed up in a process called 'recombination' before being passed on to us. Two parts of our genetic make-up, however, are passed on entirely from one parent or the other, so they don't go through the recombination process.

The first is mitochondrial DNA, which is inherited entirely from our mothers. The second is the Y chromosone, which determines the male sex and is inherited entirely from our fathers.

Differences in the genetic sequences of mitochondrial DNA and Y-chromosomal DNA – known as polymorphisms – can be identified and tracked back through generations. So, for example, we know that if two people have polymorphism A, they are descended from the same ancestor.

Adam and Eve
This has allowed researchers to work out two things about our distant ancestry:

• That we all have a female ancestor in common (known as the 'mitochondrial Eve'); and
• That all men have a male ancestor in common (known as the 'Y-chromosomal Adam').

Researchers have calculated that both 'Adam' and 'Eve' lived in Africa somewhere between 100,000 and 200,000 years ago.

This doesn't mean that they knew each other; they could have lived many thousands of years apart. But it does mean that everyone alive today (or at least everyone whose DNA has so far been examined) is descended from 'Eve' and that all men alive today are descended from 'Adam'.

DNA can also tell us a great deal about our less distant ancestry. Distinctive genetic traits can be used to identify descendants of particular groups of people. For example, families who have lived in the north east of England for generations can have genetic traits relating to the Scandinavian peoples of north western Europe that they originally inherited from the Viking settlers in that region more than 1,000 years ago.

DNA testing
The technique used to recognise and compare graphic patterns of DNA involves something called a 'blot'. In a similar fashion to using blotting paper to remove surplus ink, DNA (which can be retrieved from a minuscule sample, such as a human hair) is incorporated into a gel, which is then pressed against a sheet of material. The material is then heated to fix the DNA in place, and photographed using x-rays to create the unique 'barcode' image that many crime show viewers would recognise. By comparing these barcodes common patterns between relatives can be seen.

« What they found :Previous       Next: Q&A »

Back to top^