THE DNA DETECTIVE

All sorts of mysteries lurk in our family trees, from long-lost relatives to adoptees' hidden heritages. In the new series of DNA Family Secrets, geneticist Prof Turi King sets out to solve them with the help of presenter Stacey Dooley and home genetic testing kits. She talks to Sara Rigby

- Sara Rigby

TELL US ABOUT THE GENETIC TECHNOLOGIES YOU USE IN DNA FAMILY SECRETS.

DNA sequencing technologies have really moved on in the last 20 years. Now you can sequence entire genomes. For the medical side of things, we know a lot about genes that are involved in particular diseases, and we can tell people whether or not they have a gene that predisposes them toward something.

I got involved in the family history side of things by accident. My PhD was on the link between a surname and a Y chromosome. Surnames, like Y chromosomes, come down through the male line. So are all men with the same surname related to each other? Do they all have the same Y chromosome type? Back then the technology was based on DNA fingerprinting. We could do genetic genealogy where we could take two people with the same surname who couldn't find the genealogical links between them. We could take a look at their Y chromosomes and see if they're related.

Now it's moved on and there are direct-to-consumer testing companies. So, if somebody comes to us and says, “I don't know who my biological father is," we can get their DNA tested by one of these direct-to-consumer testing companies. They don't sequence your entire genome; they look at tiny differences, about 700,000 of them, which are places on the genome where we know people tend to differ.

We can then upload their DNA to various databases around the world and look for DNA sharing, which we measure with a unit known as a 'centimorgan'. You share half of your DNA with your parents and about half with your siblings and about a quarter with aunts and ur So, if somebody doesn't know who their father is, but knows who their mum is, you start to look for genetic matches that aren't from the mother's side. From that, you can start to build these family trees.