Since Dolly the sheep, many organisms have been cloned. Cloning involves transferring a nucleus from an adult cell into a female egg cell. For an embryo created in this way to develop into a fully formed organism, the epigenetic marks present in the adult cell nucleus, such as chemical modifications of DNA and histone proteins, must be erased and reset. Wolf studies this process, which is called epigenetic reprogramming, and believes that inefficient reprogramming is responsible for the high mortality rates of cloned animals during early development. A better understanding of epigenetics will help us to reprogramme adult cells for stem cell therapies.