Illustration of sperm cell production (spermatogenesis) within a seminiferous tubule in a testis (testicle). The spermatocytes (top two cells) divide via meiosis to form haploid (containing one set of chromosomes) spermatids (four round cells), which in turn mature into spermatozoa (bottom four cells), or sperm. Spermatozoa are the mobile male gametes (reproductive cells), which can fertilise the egg during sexual reproduction, and carry one set of chromosomes from one parent.