Although you inherit equal numbers of genes from your parents, about 200 of our 30 000 genes are imprinted – mum and dad are able to silence the gene that they pass on to their offspring. In 1991, Denise identified the first imprinted mammalian gene, which makes the insulin-like growth factor type-2 receptor or Igf2r for short. Since then, many imprinted genes that are important in development and disease have been identified. If such genes are switched off inappropriately, genetic diseases such as Prader-Willi Syndrome can result. Denise studies how non-coding RNA molecules ensure that imprinted genes remain silent.