Epigenetics is superimposed on the genetic code as an additional layer of control over our genes. Rob is investigating how genes and mobile DNA elements are controlled in plants and yeast. His team recently revealed that short ‘junk’ DNA sequences, close to points at which chromosomes pair up, play a role in silencing bits of the genome. They participate in a process called RNA interference. In plants, unlike animals, DNA methylation – another form of epigenetic silencing – is only found on repeat sequences and mobile DNA elements.