Meiosis undergo a second form of cell division that makes the sexually-reproducing organisms reproduce cells with half the number of chromosomes.
This results to a mixing or shuffled of the homologous pairs, a tendency of crossing over that causes exchanges of alleles on the homologous pairs and random fertilization unites different combinations of maternal and paternal chromosomes, which means that when zygotes are formed, the gene combination will be different each time, even if they come from the same two parents.
