In fertilization, despite numerous sperm cells surrounding an egg, only one gains entry into an egg. The one set of chromosomes in the sperm combines with the one set of chromosomes in the egg to form the zygote with two sets of chromosomes. Again, the zygote goes on to develop into the baby. Have students note that which one of the hundreds of sperm surrounding an egg gains entry and achieves fertilization is random. As yet, there is no way to select which sperm will fertilize which egg, hence no way of controlling the genetic endowment of an offspring