After S phase, what makes up a single chromosome? a. two daughter chromosomes b. a double-stranded DNA molecule c. two single-stranded DNA molecules d. two sister chromatids

Verified step by step guidance

1. Step 1: Understand the question. The question is asking what makes up a single chromosome after the S phase of the cell cycle.
2. Step 2: Recall what happens during the S phase. The S phase is part of the cell cycle where DNA replication occurs. Each chromosome is duplicated.
3. Step 3: Consider the options. Option a. 'two daughter chromosomes' is incorrect because a single chromosome does not split into two daughter chromosomes until the cell divides. Option b. 'a double-stranded DNA molecule' is incorrect because although a chromosome does contain double-stranded DNA, it is not the only component. Option c. 'two single-stranded DNA molecules' is incorrect because after replication, each chromosome consists of two double-stranded DNA molecules, not single-stranded.
4. Step 4: Choose the correct answer. Option d. 'two sister chromatids' is correct. After the S phase, each chromosome consists of two identical sister chromatids, which are copies of the original chromosome.
5. Step 5: Review the answer. After the S phase, a single chromosome is made up of two sister chromatids.

Key Concepts

Chromosome Structure

A chromosome is a structure within cells that contains DNA and proteins. After the S phase of the cell cycle, each chromosome consists of two identical halves called sister chromatids, which are joined at a region known as the centromere. This structure is crucial for ensuring accurate DNA replication and distribution during cell division.

S Phase of the Cell Cycle

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

Sister Chromatids

Sister chromatids are the two identical copies of a single chromosome that are formed during DNA replication in the S phase. They remain attached at the centromere until they are separated during mitosis or meiosis. Understanding sister chromatids is vital for grasping how genetic material is accurately distributed to daughter cells during cell division.