Regions of DNA that are undergoing transcription lack 5-methyl cytosine residues, which normally account for 1%–5% of total DNA. Evidence suggests a close correlation between methylation and gene inactivation. Regulation of DNA methylation may be responsible for imprinting control. Methylation may account for variation in phenotypic expression of some diseases.
Excerpted from BCSC 2020-2021 series: Section 2 - Fundamentals and Principles of Ophthalmology. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.