text: As cells differentiate, certain genes are silenced.  This silencing is done by modifying the histones (a sort of protein spool about which DNA is wrapped) and making the DNA rather bunched up, and inaccessible to the transcrition factors and promoters that activate a gene.  The totipotent cell requires that none of its genes are thus silenced, while cells with a silenced gene will see the same silencing in its daughter cells.