Light micrograph of crossing over between homologous stands of DNA (deoxyribonucleic acid) during diplotene of prophase I of meiosis (gamete formation). During meiosis four daughter nuclei are formed from one parent nucleus after two stages of nuclear division. Meiosis occurs only in the sex cells (gametes) of the testes and ovaries. Crossing over is a natural genetic process that occurs between homologous chromosomes and leads to the switching of genetic material between the chromosomes. This recombination increases the genetic variation in a population. Silver stain.