They preform meiosis which is the division of sex cells. This is to split the cell in to 4 instead of 2(body cells) and cut the chromosomes in half to get 23 for sex cells instead of body cells who have 46. The sex cells do this so when you put a sperm and a egg together you get 46 chromosomes to make the baby. The first cell that they make is also called tge zygote.
Hope this helps