What is crossing over?

Crossing over is a process that happens during meiosis and results in genetic variation in gametes. It happens between prophase and metaphase. Pairs of homologous chromosomes lined up next to each other touch at the same loci on each. These points of contact are called chiasmata. At these chiasmata, sections of the chromosomes break off and swap over, resulting in a reshuffling of genetic material. This is a completely normal biological process that is one of the reasons for every gamete to be completely genetically unique.