(cell biology) The first period in the interphase wherein the cell primarily grows in cell size
In eukaryotes, the cell cycle is a cyclical series of biological events that certain asexual cells go through. The cell cycle is comprised of these fundamental events: (1) resting phase (Gap 0), (2) interphase (Gap 1, S phase, Gap 2), and (3) cell division (i.e. mitotic phase and cytokinesis). The interphase is the period prior to cell division. Thus, it would entail two major events, particularly cell growth and DNA replication. The interphase is comprised of three stages: Gap 1 (G1), Synthesis phase (S phase), and Gap 2 (G2). During G1, the cell typically grows in cell size. It ends when the cell enters the S phase, which is the period when DNA is replicated. Thus, it is also during G1 phase when mRNA and proteins (histones) for DNA synthesis are produced.
In humans, the G1 phase occurs for about one third of the duration of the cell cycle, which is about 18 hours.1 Similar to other phases in the cell cycle, the G1 phase is influenced by limiting factors, e.g. temperature, nutrients, and space (for growth).
Abbreviation / Acronym: G1 (phase)
1 Morgan, D. 2007. The Cell Cycle: Principals of Control. London: New Science Press LTD.