Which of the following events during meiosis contributes most to genetic variation within a species?

• A. Formation of the spindle fibers during metaphase I
• B. Crossing over during prophase I
• C. Separation of sister chromatids during anaphase II
• D. Cytokinesis following telophase II

Answer: (B)

Verified step by step guidance

1. Understand that meiosis is a type of cell division that reduces the chromosome number by half, creating four haploid cells, each genetically distinct from the parent cell.
2. Recognize that genetic variation is crucial for evolution and adaptation, and meiosis contributes to this variation in several ways.
3. Identify the key stages of meiosis: prophase I, metaphase I, anaphase I, telophase I, prophase II, metaphase II, anaphase II, and telophase II.
4. Focus on prophase I, where homologous chromosomes pair up and exchange segments in a process called crossing over. This recombination of genetic material is a major source of genetic variation.
5. Compare crossing over with other events like spindle fiber formation, separation of sister chromatids, and cytokinesis, and understand that crossing over during prophase I is the event that contributes most significantly to genetic variation.