Epigenome effort makes its mark

When the human genome was first fully sequenced, it was often described as the recipe for making a person. In reality, the genome is more like an entire cookbook that can produce hundreds of different cell types and a staggering range of cell functions depending on which genes are switched on and off. That switching is accomplished using a vast suite of epigenetic marks — molecular and structural modifications to DNA that do not change the underlying sequence but ensure that the right genes are expressed at the right time.