Epigenetics is effectively the study of changes in gene function by covalent modifications. Such modifications result in a stably heritable phenotype that does not involve a change in DNA sequence. There are effectively 2 routes by which such covalent changes can be effected; first by methylation of C5 cytosine bases located 5’ to guanosines. This route is referred to as the cytosine methylation code. In addition, the histone component of chromosomes can be covalently modified at the N-terminus, the so-called histone code.
31 March, 2011