Well, they have to produce gametes and gametes are sex cells. So let's suppose this is the male parent. They have to produce the sperm cells. This is the female parent. They have to produce the xcels because for fertilization to actually take place, we have to have a sperm cell combined with the xcel to reform that diploid number of chromosomes to basically form that zygote. Now, we know from meiosis that during the process of meiosis when we form the gametes we have the law of segregation that is observed and what that means is the chromosomes, the homologous chromosomes actually separate.