Twins.

Identical twin Trisha Macnair meets with and interviews Professor Tim Spector who, with his team of researchers at St. Thomas' Hospital in London, has made the most detailed study of identical twins anywhere in the world. The Twin Research Unit which Spector heads is having a research day at the University of Newcastle on the genetics of attraction. Macnair attends and reports on the kind of tests taking place there, the twins participating in them and how the results may affect our understanding and treatment of genetic diseases.