The four haploid nuclei found at the end of meiosis differ from one another in their exact genetic composition, some of this difference is the result of

Options

A. Cytokinesis
B. Replication of DNA during the S-phase
C. Spindle formation
D. Crossing over during Prophase I.

Answer

To answer the question regarding the differences in genetic composition of the four haploid nuclei at the end of meiosis, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Meiosis**: Meiosis is a type of cell division that reduces the chromosome number by half, resulting in four haploid nuclei. It consists of two main stages: Meiosis I and Meiosis II.

2. **Phases of Meiosis I**: Focus on Meiosis I, particularly Prophase I, which has several sub-stages: Leptotene, Zygotene, Pachytene, Diplotene, and Diakinesis.

3. **Crossing Over**: During the Pachytene stage of Prophase I, homologous chromosomes pair up and exchange segments of genetic material in a process known as crossing over. This exchange leads to genetic recombination.

4. **Result of Crossing Over**: The result of crossing over is that the four haploid nuclei produced at the end of meiosis contain different combinations of alleles, leading to genetic diversity among the gametes.

5. **Conclusion**: Therefore, the differences in genetic composition of the four haploid nuclei are primarily due to crossing over that occurs during Prophase I of meiosis.

### Final Answer:
The four haploid nuclei found at the end of meiosis differ from one another in their exact genetic composition, some of this difference is the result of **crossing over during Prophase I**.

---