Epigenetics: The Second Genetic Code

Plant breeders utilize directed selection and transgenics to produce novel cultivars of diploid and polyploid species. DNA sequence is clearly important in these processes, but growing evidence implicates epigenetics as an important factor in controlling genetic variation and gene/transgene expression. In this article, we focus on epigenetic variation defined as mitotically and meiotically heritable but reversible states of gene expression that are not conditioned by differences in DNA sequence. We summarize mechanisms underlying epigenetic states of expression, and discuss implications of epigenetics in cultivar