Which phase of meiosis involves crossing over?

The phase of meiosis that involves crossing over is Prophase 1. This stage is crucial because it is during Prophase 1 that homologous chromosomes come together and pair up in a process called synapsis. This close pairing allows for the exchange of genetic material between non-sister chromatids, leading to genetic recombination. The result is increased genetic diversity in the offspring, which is a fundamental aspect of sexual reproduction.

During Prophase 1, various sub-stages occur, including leptotene, zygotene, pachytene, diplotene, and diakinesis. It is particularly in the pachytene stage that crossing over is most prominent, as the exchanges of segments of DNA between chromatids occur. The recombination events create new combinations of alleles, contributing to genetic variation in future generations.

Other phases of meiosis, such as Metaphase 1, Telophase 2, and Anaphase 2, do not involve crossing over. Metaphase 1 is characterized by the alignment of homologous pairs along the cell's equatorial plane, while Telophase 2 and Anaphase 2 involve the separation of sister chromatids and subsequent formation of gametes.