DNA Replication and Repair (1B) Practice Test

In a yeast model, a single gene knockout produces normal DNA synthesis rates but causes frequent small insertions and deletions specifically within short repeated sequences (e.g., AAAAAA). The phenotype is strongest after many rounds of cell division and is reduced when a second gene that promotes recombination is overexpressed. Based on the scenario, which outcome is most consistent with loss of the primary pathway that corrects small loops formed during copying of repetitive DNA?

In a model organism study, embryos carrying a temperature-sensitive mutation in DNA ligase develop normally at $25^\circ\text{C}$ but show extensive chromosome fragmentation and cell-cycle arrest at $37^\circ\text{C}$. DNA sequencing does not show a marked increase in base substitutions, but microscopy reveals many persistent single-strand breaks. Which statement best explains the role of DNA ligase in DNA replication that is most consistent with these findings?