Which of the following is true for crossing over? (i) Crossing over is the exchange of genetic material between two homologous chromatids. (ii) Crossing over is also an enzyme-mediated process and the enzyme involved is called recombinase. (iii) Crossing over leads to recombination of genetic material on the two chromosomes. (iv) Recombination between homologous chromosomes is completed by the end of diplotene. (v) Crossing over started in pachytene. (vi) It is responsible for variation in organism.