Crossing over is possible due to what event that occurs in Meiosis I but not in Mitosis?

• A. Separation of sister chromatids
• B. Formation of the mitotic spindle
• C. Cytokinesis
• D. Synapsis of homologous chromosomes

Answer: (D)

Verified step by step guidance

1. Understand that crossing over is a process where homologous chromosomes exchange genetic material during meiosis, leading to genetic diversity.
2. Recognize that meiosis consists of two stages: Meiosis I and Meiosis II. Crossing over occurs during Prophase I of Meiosis I.
3. Identify that synapsis is the pairing of homologous chromosomes during Prophase I of Meiosis I, which allows crossing over to occur.
4. Differentiate between meiosis and mitosis: In mitosis, homologous chromosomes do not pair up, and thus, crossing over does not occur.
5. Conclude that the event unique to Meiosis I that facilitates crossing over is the synapsis of homologous chromosomes, which does not occur in mitosis.