Identify the incorrectly matched pair in the given options .

Options

A. DNA duplication - S - phase
B. Reductional division - Meiosis
C. Equational division - Mitosis
D. Crossing over - Sister chromatids of homologous chromosomes.

Answer

To solve the question of identifying the incorrectly matched pair, we will analyze each option provided in the question step by step.

### Step 1: Analyze the First Option - DNA Duplication and S Phase
- **Explanation**: DNA duplication occurs during the S phase of the cell cycle. This is the phase where DNA synthesis takes place, and the genetic material is replicated.
- **Conclusion**: This match is correct.

### Step 2: Analyze the Second Option - Reductional Division and Meiosis
- **Explanation**: Meiosis is known as reductional division because it reduces the chromosome number by half, producing haploid cells from a diploid cell. This is a characteristic feature of meiosis.
- **Conclusion**: This match is correct.

### Step 3: Analyze the Third Option - Equational Division and Mitosis
- **Explanation**: Mitosis is referred to as equational division because the daughter cells produced have the same number of chromosomes as the parent cell. There is no change in the chromosome number during mitosis.
- **Conclusion**: This match is correct.

### Step 4: Analyze the Fourth Option - Crossing Over and Sister Chromatids of Homologous Chromosomes
- **Explanation**: Crossing over occurs between non-sister chromatids of homologous chromosomes, not between sister chromatids. Sister chromatids are identical copies of a single chromosome, while non-sister chromatids are from different homologous chromosomes.
- **Conclusion**: This match is incorrect.

### Final Answer
The incorrectly matched pair is the fourth option: "Crossing over and sister chromatids of homologous chromosomes."

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