Leland Hartwell, the third recipient of the 2001 Nobel Prize in Physiology or Medicine, was acknowledged for

Question:

Leland Hartwell, the third recipient of the 2001 Nobel Prize in Physiology or Medicine, was acknowledged for his characterization of cell cycle checkpoint pathways in the budding yeast S. cerevisiae. What is a cell cycle checkpoint pathway? When during the cell cycle do checkpoint pathways function? How do cell cycle checkpoint pathways help to preserve the genome?