I found this excellent description in Amy Yasko's forum: ch3nutrigenomics.com. It was posted by one of the members on the site- raji: http://www.ch3nutrigenomics...
This is a private blog, but it is a very rich source of information about methylation, nutrigenomics and dietary supplementation
Here is a copy of the post:
Methyl group: A methyl group is simply a single carbon atom bonded to 3 hydrogen atoms (CH3).
Methylation: Transfer of methyl groups from one chemical to another is called methylation. Essentially any chemical compound that has a methyl group as part of its chemical ... ..more