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. Respiration of DNA during the S phase
C. Spindle formation
D. Crossing over during Prophase I.

Answer

**Step-by-Step Text Solution:**

1. **Understanding Meiosis**: Meiosis is a type of cell division that reduces the chromosome number by half, resulting in four haploid nuclei. Each of these nuclei contains a unique combination of genetic material.

2. **Homologous Chromosomes**: In meiosis, chromosomes are present in pairs known as homologous chromosomes. Each pair consists of one chromosome from each parent.

3. **Non-Sister Chromatids**: Within these homologous chromosomes, there are non-sister chromatids. These are the chromatids from different homologous chromosomes.

4. **Crossing Over**: During prophase I of meiosis, a process called crossing over occurs between non-sister chromatids. This involves the exchange of genetic material between chromatids of homologous chromosomes.

5. **Recombination**: The result of crossing over is genetic recombination, which leads to new combinations of alleles. This recombination is a significant source of genetic diversity among the haploid nuclei produced at the end of meiosis.

6. **Phase of Meiosis**: It is important to note that crossing over specifically occurs during prophase I of meiosis, which is divided into several sub-stages (leptotene, zygotene, pachytene, diplotene, and diakinesis).

7. **Conclusion**: Therefore, the differences in genetic composition among the four haploid nuclei at the end of meiosis are primarily due to crossing over during prophase I.

**Final Answer**: The differences in genetic composition are the result of crossing over during prophase I.

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