[1][2] It is initiated specifically against alkylation, particularly methylation, of guanine or thymine nucleotides or phosphate groups on the sugar-phosphate backbone of DNA.
[3][4] Environmental influence plays a crucial role in the developmental plasticity of genotypes due to the introduction of DNA damaging agents.
This phenomenon and the defense mechanism that has evolved to protect an organism’s genotype against damage and prevent multiple phenotypes is known as the adaptive response.
[1] The alkA gene product is a glycosylase that can repair a variety of lesions, removing a base from the sugar-phosphate backbone, producing an abasic site.
It has recently been suggested that specific mechanistic pathways of the adaptive response can activate the important tumor suppressor protein p53.
A key experiment that reveals the underlying mechanisms is that which involves the treatment with protein synthesis inhibitors to Oedogonium Chlamydomonas and Closterium cells.