Environmental epigenomics: understanding the effects of parental care on the epigenome.

An organism's behavioural and physiological and social milieu influence and are influenced by the epigenome, which is comprised predominantly of chromatin and the covalent modification of DNA by methylation. Epigenetic patterns are sculpted during development to shape the diversity of gene expression programmes in the organism. In contrast with the genetic sequence, which is determined by inheritance and is virtually identical in all tissues, the epigenetic pattern varies from cell type to cell type and is potentially dynamic throughout life. It is postulated that different environmental exposures could effect epigenetic patterns relevant for human behaviour. Because epigenetic programming defines the state of expression of genes, epigenetic differences could have the same consequences as genetic polymorphisms. Yet in contrast with genetic sequence differences, epigenetic alterations are potentially reversible. In the present chapter, we will discuss evidence that epigenetic processes early in life play a role in defining inter-individual trajectories of behaviour, with implications for mental health in adulthood.