There are three main arguments:
· The main important motive is because we have diploid cells, but they’re not
always in that way; some cells are haploids, because of meiosis. Since in sexual reproduction, the parents’ gametes (these are diploid cells) mix each other. In each person, its cells get divided by mitosis, and especially by meiosis. This last one, meiosis, is very complex, and it can originate lots of different haploid cells. The scientists have investigated and calculated that we can originate about eight million of different cells, because of the distribution of the chromosomes.
· Another important argument is the
combination of the gametes of each parent; the father’s mixes with mother’s. This can originate about seventy million of different individuals.
· But although you don’t believe, there is other motive that is very unbelievable: Crossing-over. When the cell is on Meiosis I (there are Meiosis I and II), on Prophase I, cells experiment a change, an alteration of genes, since some them (complete genes) move with other genes on the same position, between one chromosome and the other of the same pair. This originates a different genetic code. It can be a new combination that had never existed.