When does crossing over take place during meiosis?

Crossing over takes place during Prophase I of meiosis. This is a critical phase where homologous chromosomes pair up and exchange genetic material. The process of crossing over occurs at points called chiasmata, where the arms of homologous chromosomes intertwine and segments of DNA are swapped. This genetic recombination is essential for increasing genetic diversity in offspring, as it results in new combinations of alleles.

During Prophase I, the chromosomes condense, and the nuclear envelope begins to break down, allowing for the physical interaction of homologous chromosomes. This distinguishes it clearly from other phases of meiosis, where the chromosomes do not undergo this critical process of genetic exchange and pairing. The events of Metaphase I, Anaphase I, and Telophase I involve the alignment, separation, and division of chromosomes, respectively, but not the actual crossing over of genetic material.