During which phase of meiosis does crossing over occur?

Crossing over occurs during Prophase I of meiosis. This phase is crucial for genetic diversity, as it involves the exchange of genetic material between homologous chromosomes. During Prophase I, homologous chromosomes pair up in a process called synapsis, forming structures known as tetrads. Within these tetrads, segments of DNA can be exchanged between non-sister chromatids in a process facilitated by the formation of structures called chiasmata. This recombination results in new allele combinations, which increases genetic variation in the gametes produced.

In contrast, the other phases of meiosis do not include crossing over. For instance, Metaphase I is characterized by the alignment of homologous chromosome pairs at the equatorial plane of the cell, while Anaphase I involves the separation of homologous chromosomes to opposite poles. Telophase II and subsequent cytokinesis address the division of the two haploid cells formed at the end of meiosis, but they do not involve the activity of crossing over.