DNA methylation

DNA methylation is the main way gene activity is adjusted during life, especially during early development.^[1]

Illustration of a DNA molecule that is methylated at the two center cytosines. DNA methylation plays an important role for epigenetic gene regulation in development and disease

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.^[1][2]

Suppressing genes is the basis of epigenetics, the study of changes in gene activity which are not caused by changes in the DNA sequence.^[3] It is the study of gene expression, the way genes bring about their phenotypic effects.^[4]

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.^[1][5]

• 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.^[6]