In a typical eukaryotic cell cycle, which phase occurs immediately after cytokinesis has been completed?

Introduction / Context:
The eukaryotic cell cycle is a carefully ordered series of phases that allows cells to grow, duplicate their genetic material, and divide into two daughter cells. Understanding the correct sequence of these phases is essential in cell biology, genetics, and medicine. Cytokinesis is the final step of the M phase, where the cytoplasm divides and two physically separate daughter cells are formed. This question asks which specific phase comes immediately after cytokinesis in the normal, repeated cell cycle of a typical eukaryotic cell.

Given Data / Assumptions:

• Cytokinesis is considered the last part of the M phase (mitotic phase).
• The standard phases of the cell cycle are G1, S, G2, and M.
• The options list S phase, G1 phase, G2 phase, and a repeated M phase.
• We assume a typical somatic cell that continues cycling and is not entering a prolonged resting state such as G0.

Concept / Approach:
The cell cycle is usually summarised as G1 → S → G2 → M → back to G1. During the M phase, the nucleus divides in mitosis and the cytoplasm divides in cytokinesis. Once cytokinesis is complete, the two daughter cells enter interphase, beginning with the G1 phase. In G1, cells grow, produce RNA and proteins, and prepare for DNA replication. Only after G1 do they move into S phase, where DNA synthesis occurs, followed by G2, which prepares the cell for the next mitosis. Therefore, the correct approach is to identify G1 as the immediate successor to cytokinesis.

Step-by-Step Solution:
Step 1: Recall that cytokinesis marks the end of the M phase, leaving two newly formed daughter cells. Step 2: Remember that after the M phase, the cell re-enters interphase and begins with the G1 phase, which is a growth and preparation period. Step 3: Note that the S phase, where DNA is replicated, does not occur until after G1 is completed. Step 4: Recognise that the G2 phase comes after S phase and immediately precedes the next mitosis, so it cannot follow cytokinesis directly. Step 5: Understand that M phase is not immediately repeated under normal conditions; cells typically go through an entire interphase before dividing again. Step 6: Conclude that the G1 phase of interphase is the phase that occurs directly after cytokinesis.

Verification / Alternative check:
Many cell cycle diagrams in textbooks show a circle with M phase occupying a relatively small segment, followed by a long interphase consisting of G1, S, and G2. In these diagrams, the arrow from cytokinesis points directly into G1. Experimental evidence supports this: immediately after cell division, daughter cells begin to grow and build up proteins and organelles before DNA replication begins, which is characteristic of G1. Additionally, cell cycle checkpoints such as the G1 checkpoint regulate whether the cell proceeds to S phase, indicating that G1 must precede S after every mitosis. These consistent representations confirm that G1 comes right after cytokinesis.

Why Other Options Are Wrong:
S phase is the period of DNA synthesis that follows G1. It does not start immediately after cytokinesis; instead, the cell must first pass through G1, so this option is incorrect as the immediate next phase.
G2 phase occurs later in interphase, after S phase is complete. It prepares the cell for mitosis, not for the immediate post division growth, so it cannot be the phase right after cytokinesis.
M phase again suggests that the cell would perform mitosis and cytokinesis repeatedly without going through interphase. This does not occur in the normal cell cycle, making this option incorrect for typical cycling cells.

Common Pitfalls:
A frequent mistake is to confuse the order of interphase stages and assume that any of G1, S, or G2 could follow cytokinesis directly. Another pitfall is forgetting that interphase is not a single homogeneous phase but has distinct stages with specific roles. Some learners also mistakenly think that DNA must be replicated immediately after division, leading them to choose S phase. To avoid these errors, remember the correct order G1 → S → G2 → M and the idea that cells first grow and prepare in G1 before copying their DNA in S.

Final Answer:
In a typical eukaryotic cell cycle, the phase that occurs immediately after cytokinesis is the G1 phase of interphase (first gap phase).