The first step is the reverse of glycine biosynthesis from serine with serine hydroxymethyl transferase.
From the en.wikipedia.org
Previous research had shown that the methyl tags on sperm DNA are converted to their chemical cousin, hydroxymethyl, before disappearing completely.
From the sciencedaily.com
Through a high resolution staining technique, he was able to compare the levels of methyl tags and hydroxymethyl tags in sperm and egg chromosomes at early developmental stages of life.