Can there be mitosis without DNA replication in 'S' phase?
No, there cannot be mitosis without DNA replication in the 'S' phase. The S phase marks the period during which DNA synthesis or replication takes place. During this phase, the amount of DNA per cell doubles (e.g., from 2C to 4C), which is essential for the cell to divide.
Prophase, the first stage of mitosis, follows the S and G₂ phases. The text establishes a sequence where DNA replication must occur before mitosis begins. If the DNA is not replicated in the S phase, the cell cannot proceed to mitosis, as the genetic material would not be sufficient to form daughter cells with the correct chromosome number.
Explanation
The textbook context explicitly defines the S phase as the period where DNA replication takes place, increasing the DNA content from 2C to 4C. It further states that Prophase (the start of mitosis) follows the S and G₂ phases. Therefore, the standard cell cycle sequence dictates that DNA replication is a prerequisite for mitosis. Without the events of the S phase, the genetic material is not duplicated, preventing the cell from entering mitosis.
Solution Steps
Step 1: Identify the function of the 'S' phase from the text. The text states, 'S or synthesis phase marks the period during which DNA synthesis or replication takes place.'
Step 2: Identify the sequence of the cell cycle. The text states, 'Prophase which is the first stage of karyokinesis of mitosis follows the S and G₂ phases.'
Step 3: Conclude that mitosis depends on the preceding S phase. Since mitosis follows the S phase, and the S phase is required for DNA duplication, mitosis cannot occur without DNA replication in the S phase.