The correct option is D All of the above
In sexually reproducing organisms, the new organism is formed by the union of cells from the mother and the father. In order to create a diploid organism, the uniting cells must be haploid so as to maintain the constant chromosome number in the baby. Gametes are haploid cells formed from special diploid cells by meiotic cell division.
In prophase I of meiosis I, the homologous chromosomes of the parent cell pair together and the non-sister chromatids of the homologous chromosomes crossover and exchange genetic information. This crossing over leads to recombination of genetic material which generates variations.