Cell Cycle Practice Test

Cells in a tissue are exposed to ionizing radiation that produces double-strand breaks in DNA during G1. A normal G1 checkpoint can delay entry into S phase when DNA damage is detected, preventing replication of damaged templates. In one experimental group, a protein required for the G1 checkpoint is inhibited, so cells enter S phase on schedule even though breaks remain unrepaired. DNA replication proceeds across the genome, and cells later enter G2 with duplicated chromosomes. Which outcome is most likely for these cells as they progress through the cycle?

In a dividing cell, chromosomes condense and the nuclear envelope breaks down. During metaphase, all chromosomes align at the metaphase plate. Imaging reveals that for several chromosomes, both sister kinetochores are attached to microtubules from the same spindle pole, while other chromosomes show attachments to opposite poles. The cell proceeds into anaphase without a prolonged metaphase delay. After cytokinesis, one daughter cell contains extra copies of some chromosomes while the other is missing those chromosomes. Which checkpoint failure most directly explains the observed daughter-cell chromosome imbalance?