The correct answer would be crossing over that takes place during prophase 1 of meiosis 1.
Crossing over maintains genetic diversity within an organism population, permits different genetic recombination to be transferred from parents to their offspring.
Crossing over of chromatids pair takes place in prophase-I, it is the very first phase of meiosis-1. In this phase, the 3rd subphase is pachytene in which genetic recombination occurs due to the formation of recombinant nodules.
Thus, the correct answer is crossing over that takes place during prophase 1 of meiosis 1.
The process is known as meiosis
Mitosis and meiosis are two ways in which a cell divides into eukaryotic organisms. Although both processes share several stages, they also have important differences. While mitosis is a method where a cell is cloned, obtaining two cells with identical genetic information. In meiosis four daughter cells are obtained that are genetically different from each other, and also different from the progenitor cell.
A cell must undergo the process of meiosis in order to have genetically different cells at the end of cell division. Meiosis produces four daughter (haploid) cells, each of which is genetically distinct from the parent cell from which they arose.