DNA methylation

DNA methylation is the main way gene activity is adjusted during life, especially during early development.

It is how methyl groups are added to DNA.  This suppresses gene transcription.  Two of DNA's four nucleotides, cytosine and adenine, can be methylated. Since adenine methylation is restricted to prokaryotes, all eukaryote transcription is regulated by suppressing cytosine.Law, Julie A. & Jacobsen S.E. 2012. Establishing, maintaining and modifying DNA methylation patterns in plants and animals. Nature Reviews in Genetics 11 (3) 204–220. Carey, Nessa 2011. The epigenetics revolution: how modern biology is rewriting our understanding of genetics, disease and inheritance. London: Icon Books. ISBN 978-184831347-7

Suppressing genes is the basis of epigenetics, the study of changes in gene activity which are not caused by changes in the DNA sequence.By "DNA sequence" we mean the sequence of nucleotide base pairs in an exon, which is the part of a gene which determines the sequence of amino acids in the coded protein. It is the study of gene expression, the way genes bring about their phenotypic effects.King R.C. Stansfield W.D. & Mulligan P.K. 2006. A dictionary of genetics, 7th ed. Oxford. p146

The changes in gene activity by methylation may last for the rest of the cell's life, and for many generations of cells through cell divisions. However, there is no change in the underlying DNA sequence of the organism. Instead, non-hereditary factors cause the organism's genes to behave (express themselves) differently.Bird A. (2007. Perceptions of epigenetics. Nature 447 (7143): 396–8. 

To give just one example of how important this is, think about the effect nutrition of a pregnant female has on the baby long after birth.Carey, p93

 References 

Category:Cell biology
Category:DNA
Category:Developmental biology
Category:Molecular biology
Category:Epigenetics