The diagram below shows part of the cell cycle. Normally, checkpoints exist between each phase that monitor whether a cell is ready to move onto the next phase of cell cycle. An error at which of the following checkpoints would be most likely to lead to uncontrolled cell division and cancer?
the checkpoint that prevents cells from leaving M phase until they are ready
the checkpoint that prevents cells from leaving S phase until they are ready
the checkpoint that prevents cells from leaving G1 phase until they are ready
the checkpoint that prevents cells from leaving G2 phase until they are ready

"1. it should be, it has been for about 20 years, and it's really not much different in the end than breeding animals to have particular traits. there are always concerns about genetically engineered animals/plants affecting the environment in unexpected negative ways, but i can't think of an example where the fears didn't turn out to be baseless.  

first, as you point out, it would be a great advance in pharmacology, to be able to tailor drugs and their doses to me. the pros involve better medical treatment. the cons involve privacy issues like insurance companies denying coverage to people with genetic risk factors. looking at dna markers wouldn't affect the frequency of genetic diseases, but it would allow detection of them earlier. and ok, actually i suppose that if people used this information to avoid having children with genetic diseases, some might decrease in frequency."