Final answer:
A malfunctioning G2 checkpoint can result in cells entering mitosis with unreplicated or damaged DNA, leading to genomic instability and an increased risk of cancer development.
Step-by-step explanation:
If the G2 checkpoint stopped working, cells would enter mitosis without ensuring that all chromosomes have been properly replicated and that the DNA is undamaged. This could lead to the propagation of cells with genomic instability, a hallmark of cancer cells. Cells could then accumulate mutations at a higher rate, leading potentially to the development of cancer due to the unchecked growth and division of these aberrant cells. Moreover, a mutation producing abnormal cyclin-dependent kinase (Cdk) at the G2/M checkpoint could further the advancement of the cell cycle without proper regulation, exacerbating the problem.