Sperms and eggs are made differently. These sex cells need only one out of each pair of chromosomes. Otherwise, a baby would have twice as many chromosomes as its parents. So each sex cell only has 23 chromosomes, one from each pair. This special kind of cell division is called meiosis (my-o-sis). It makes four cells, each with just half the number of chromosomes of the original cell. These cells become sperm cells or egg cells. Cell division by meiosis