Which of the following occurs during S phase? (A) condensation of the chromosomes (B) replication of the DNA (C) separation of sister chromatids (D) spindle formation

Verified step by step guidance

1. Identify the phase of the cell cycle in question: S phase is part of the cell cycle where DNA replication occurs in preparation for cell division.
2. Eliminate options not related to DNA replication: (A) Condensation of the chromosomes occurs during prophase of mitosis, not S phase. (C) Separation of sister chromatids occurs during anaphase of mitosis, not S phase. (D) Spindle formation occurs during prophase of mitosis, not S phase.
3. Focus on the correct option: (B) Replication of the DNA is the hallmark of S phase, where each chromosome is duplicated to ensure that each new cell will receive an identical set of chromosomes.
4. Understand the process: During S phase, the entire genomic DNA in the nucleus is replicated, leading to the formation of two identical copies (sister chromatids) held together at the centromere.
5. Confirm the answer: The correct answer is (B) replication of the DNA, as this is the primary event that occurs during the S phase of the cell cycle.

Key Concepts

S Phase of the Cell Cycle

The S phase, or synthesis phase, is a crucial part of the cell cycle where DNA replication occurs. During this phase, each chromosome is duplicated, resulting in two sister chromatids for each chromosome. This ensures that when the cell divides, each daughter cell receives an identical set of chromosomes.

DNA Replication

DNA replication is the biological process of producing two identical replicas of DNA from one original DNA molecule. This process involves unwinding the double helix and synthesizing new strands using the original strands as templates. It is essential for cell division, ensuring that genetic information is accurately passed on to daughter cells.

Chromosome Structure

Chromosomes are structures within cells that contain DNA and proteins. They exist in a condensed form during cell division, but during the S phase, they are in a less condensed state as they are being replicated. Understanding chromosome structure is vital for grasping how genetic material is organized and how it behaves during cell division.