What is crossing over? In which period of meiosis does this event occur?
Crossing over is the eventual exchange of chromosomal fragments among homologous chromosomes. The phenomenon happens in prophase I when homologous chromosomes are paired. Crossing over is of great importance for evolution and biodiversity as it provides recombination of alleles (of dissimilar genes) linked in the same chromosome during cell divison by meiosis.
Cell Division Review - Image Diversity: crossing over