Large-scale studies such as the Avon Longitudinal Study of Parents and Children are playing a fundamental role in helping scientists to identify distinctions between the effects of genes and environment on our bodies and minds. Not only will this point the way to new treatments for disease, it will also illuminate the critical factors that determine who we are.

However, taking part in such studies exploring genetic risk factors for disease could have profound effects on our lives and identities. If the study identified that we had a high risk of a disease, such as breast cancer, but that there was no certainty we would actually get it, for example, would we want to know about the risk?

Would we want to live with the fear of something that may not happen? Would we take drastic preventative action, such as having both our breasts removed, to pre-empt the cancer occurring, even though such operations cannot remove all the tissue that is likely to become cancerous? What about the effects of such 'knowledge' on our sense of safety, our social relationships and life decisions such as whether to marry and have children?