What does crossing over refer to in meiosis?

Crossing over is a crucial process during meiosis that specifically involves the exchange of genetic material between homologous chromosomes. During prophase I of meiosis, homologous chromosomes pair up in a process called synapsis. While in this paired state, segments of chromatids from one homologous chromosome can break and reattach to the corresponding segments on the other homologous chromosome. This exchange of DNA results in new combinations of alleles, significantly contributing to genetic diversity in the gametes produced.

By facilitating the mixing of parental genes, crossing over is fundamental to evolutionary processes and enhances the variation that is essential for natural selection. The resulting chromatids, after crossing over, carry different genetic information compared to the original parental chromatids. This genetic recombination is key to the process of meiosis and plays an important role in the inheritance of traits in offspring.