Activation of proto-oncogenesis appears to be the same, regardless of the specific cause, in the mechanism of carcinogenesis. These proto-oncogenes were the genes that directed normal early embryonic development. At about 8 days after conception, these genes should normally be controlled forever. They are turned off, controlled or suppressed by "suppressor genes" that can act directly at the DNA level, preventing the proto-oncogene from being over-expressed. Another way that the suppressor genes work is by preventing cells from dividing, or maintaining control over the cell cycle.