PATHOLOGY

Detailed explanation-1: -These studies confirm that UV is an S-phase-dependent clastogen and point to the G1 /S border as a time of maximal sensitivity to clastogenesis. Irradiation of G1 cells was shown to produce a fluence-dependent reduction in the rate of entry of cells into the S-phase.

Detailed explanation-2: -Following a low dose of UV radiation, DNA replication is inhibited and the cells undergo a transient arrest re-entering the cell cycle by 24 h. Instead, a high dose of UV damage leads to an initial replicative arrest followed by death of the cells by apoptosis.

Detailed explanation-3: -The primary G1/S cell cycle checkpoint controls the commitment of eukaryotic cells to transition through the G1 phase to enter into the DNA synthesis S phase.