Crossing over occurs in meiosis during which phase?

• A. Metaphase II
• B. Anaphase I
• C. Telophase I
• D. Prophase I

Answer: (D)

Crossing over is the genetic exchange between homologous chromosomes, which occurs when they pair up during meiosis. That pairing, called synapsis, happens in prophase I, when homologs align to form a tetrad and non-sister chromatids exchange segments at sites called chiasmata. This recombination, especially prominent during the pachytene stage of prophase I, creates new combinations of alleles on each chromosome and contributes to genetic diversity. After prophase I, the chromosomes are prepared to separate, and crossing over does not occur again in later phases such as metaphase II, anaphase I, or telophase I.