The cell cycle is a set of periodic events each cell will
experience before successful division with distinct sequential
phases such as G1 (Gap 1), S (DNA synthesis), G2 (Gap 2)
and M (mitosis) (Fig.2). Cell-cycle progression was simply
defined as “clock + checkpoint”, since it has clock-like
periodicity and switch-like ‘check-points’ where a yes-or-no
decision is made about the next event (Aghaeepour et al.,
2013).