Discovery of Crossing Over: Belgian Cytologist Janssens (1909) noticed chiasmata formation during the prophase of meiosis I. Morgan (1910) found that chiasmata formation leads to the crossing over of alleles by breakage and reunion of homologous chromosomes. What is Crossing Over? Crossing Over occurs during meiosis I while homologous chromosomes have synapsed. Crossing Over may be defined as the exchange of a part of a chromatid from one homologous chromosome with an equivalent part of a chromatid from the other homologous chromosome. This exchange results in a new gene combination. Remember that a chromosome is a double strand of DNA. … Continue reading Crossing Over (Genetic Recombination)