Modern biology is rewriting our understanding of genetics, disease and inheritance.
There are lots of situations where two things that are the same at the DNA level are different in appearance and behaviour. These tell us that there is more to life than just the genetic code, and they are known as epigenetic phenomena.
Think of a caterpillar and a butterfly, or a slipper limpet that can change its sex as an adult shellfish. Identical twins become more dissimilar as they age, despite sharing an identical DNA script. The differences can even be as extreme as one twin developing a serious disease while the other remains completely healthy.
Scientists are starting to understand how these epigenetic differences are created and maintained. The process depends on a complex set of chemicals that our cells add to our genes. These chemical changes controls how genes are expressed, so that the same genetic code can create different outcomes. They can also have unexpected effects.
For example, epigenetics is very significant to human health and disease and may have a role in a wide range of conditions from chronic diseases such as rheumatoid arthritis and schizophrenia, to drug addiction and to the long term effects of abusive or neglectful childhoods. It is also known to be important in cancer.
Sometimes, epigenetic effects may even be passed on from parent to child. Children born to mothers who have lived through starvation may have increased susceptibilities to various diseases later in life. Animal studies have suggested that fear itself may be passed down to offspring.
Nessa Carey has a virology PhD from the University of Edinburgh and is a former Senior Lecturer in Molecular Biology at Imperial College, London. She has worked in the biotech and pharmaceutical industry for ten years.