Final answer:
A gene expressed solely during the S-phase is likely involved in DNA replication, as this phase is dedicated to the duplication of the cell's DNA. Other processes like photosynthesis, transcription, and root development are not specifically tied to the S-phase.
Step-by-step explanation:
If a gene is expressed exclusively during the S-phase of the cell cycle, it is most likely involved in DNA replication. The S-phase, or Synthesis phase, is characterized by the duplication of the cell's DNA, ensuring that each daughter cell receives an identical set of genetic information upon division. Crucial proteins like DNA polymerases, helicases, and primases are synthesized during this phase to drive the process of replication.
Photosynthesis, transcription, and root development are not processes directly associated with the S-phase. Photosynthesis occurs in chloroplasts of plant cells and is independent of the cell division cycle. Transcription can occur during multiple phases of the cell cycle, not just S-phase, to produce RNA from DNA. Root development is a more complex process involving cell division, elongation, and differentiation, which extends beyond just the S-phase.
Therefore, a gene specifically expressed in cells undergoing S-phase is most appropriately linked to the fundamental mechanisms of DNA replication within the cell cycle. This ensures proper genetic continuity for cell proliferation.