In area cells, the checkpoint proteins are often abnormal, allowing damaged DNA to be replicated and passed to daughter cells. This is how area are copied from one cell to the next. If there is a mutation in a gene that normal controls growth, then the cell will not have normal area of growth. A cell with defective checkpoint proteins can result in cancer, the area growth of cells with mutated DNA.

How cells use checkpoints at the end of G1 phase, end of G2 phase, and partway Normal cells, however, move through the cell cycle in a regulated way.

Explanation:

the answer will be a) proteins i believe

"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."