The sperm (spermatozoon) is the male reproductive cell that carries the paternal (father’s) haploid genome. Each sperm cell consists of a head (containing the sperm nucleus), a midpiece (containing mitochondria), and a flagellar tail. Spermatozoa are fully formed when they leave the testis but must undergo additional maturation processes in the epididymis and female reproductive tract (capacitation) before they are capable of fertilizing an egg.