Crossing over between homologous chromosomes takes place during
- A. metaphase I
- B. anaphase I
- C. prophase I
- D. telophase II
Explanation
During the pachytene stage of prophase I the homologues are paired as bivalents, and non sister chromatids exchange equal segments at points called chiasmata. Pairing must happen before the chromosomes line up on the spindle, so no later stage can allow the exchange. The chiasmata remain visible into metaphase I and hold the bivalent together.
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