During which of the following stages of interphase is mRNA synthesized?

During the G1 phase of interphase, the cell is actively growing and synthesizing various molecules needed for DNA replication and cell function. This is the phase when mRNA synthesis occurs as the cell prepares for DNA synthesis in the subsequent phase.

During G1, the cell engages in transcription, which is the process of synthesizing mRNA from DNA templates. This mRNA is crucial because it carries the genetic information necessary for the synthesis of proteins that support cellular functions and the progression of the cell cycle.

In contrast, the S phase is primarily focused on DNA replication, where the cell duplicates its DNA in preparation for cell division. Prophase and M phase (mitosis) are associated with the actual division of the nucleus and the segregation of chromosomes, not with mRNA synthesis. Hence, the G1 phase is the correct answer as it is specifically focused on growth and the synthesis of molecules, including mRNA.