DNA methylation expression is a process that regulates gene activity by adding or removing chemical groups called methyl groups to DNA. These modifications can turn genes "on" or "off" by affecting their accessibility to cellular machinery. Methylation influences cell specialization, development, and bodily functions. It is studied to understand its impact on biology and health, including diseases like cancer. In summary, DNA methylation expression controls gene activity through chemical modifications, shaping development and impacting biological processes.