What happens during crossing over in meiosis?

During meiosis, crossing over refers to the process wherein homologous chromosomes, which are similar in size and genetic content, exchange segments of their chromatids. This occurs during prophase I of meiosis when these chromosomes are paired closely along their lengths.

The significance of crossing over lies in its contribution to genetic diversity. By exchanging genetic material, crossing over creates new combinations of alleles on each chromosome. This increases the genetic variation in the gametes produced, which is crucial for evolution and adaptation.

Other processes mentioned in the choices describe different phases or actions during meiosis but do not pertain specifically to crossing over. For instance, chromosome replication occurs earlier in the cell cycle, during interphase, to duplicate the genetic material before meiosis begins. Chromosomes aligning at the equator occurs during metaphase I and metaphase II of meiosis, and the formation of gametes happens as a result of the entire meiotic process, culminating with the final cell division, not during the crossing over event itself.