From what I'm reading methylation isnt permanent and is a common occurence. The DNA sequence isnt altered... the genes themselves arent altered. The methyl groups can supress the transcription of genes... but remove the methyl group and the gene will get transcribed.
Just quick note from Wiki:
DNA methylation is a process by which
methyl groups are added to the DNA molecule. Methylation can change the activity of a DNA segment without changing the sequence. When located in a gene
promoter, DNA methylation typically acts to repress gene
transcription. In mammals DNA methylation is essential for normal development and is associated with a number of key processes including
genomic imprinting,
X-chromosome inactivation, repression of
transposable elements,
aging, and
carcinogenesis.
