Coloured scanning electron micrograph (SEM) of human sperm (spermatozoon, spermatozoa). A spermatozoon (motile male sperm) joins an ovum (female egg) to form a zygote. A zygote is a single cell, with a complete set of chromosomes, that normally develops into an embryo.) Sperm cells contribute approximately half of the nuclear genetic information to the diploid offspring (excluding mitochondrial DNA). Magnification: x725 when shortest axis printed at 25 millimetres.