From The London Times:
The Twin Research and Genetic Epidemiology Unit at St Thomas’ Hospital, London, is the largest unit in the world performing regular clinical trials involving 10,000 twin volunteers. The basis of its studies on twins is relatively simple, focusing on the principle that identical twins have the same genes, non-identical twins don’t. Twin studies compare traits in these two groups. Twins from both groups are likely to have been exposed to similar environmental influences, but only twins in the identical group have the same genes. The Twin Research Unit finds out which traits and illnesses are partly influenced by the genes that we are born with. It has identified an important genetic component in the following conditions:
Osteoarthritis, previously believed to be caused by “wear and tear” Short-sightedness Perfect pitch Acne Cataracts — a disease of ageing, but its severity is down to your genes Migraine, high blood pressure and coronary artery disease — which also seem to involve the same gene Infidelity — the tendency for both twins to be either faithful or unfaithful was strongest in identical pairs.