Human fertilization. Artwork of numerous sperm cells (spermatozoa) surrounding a human egg cell (ovum, round, centre). The sperm cells consist of a head section and a tail section. They are trying to penetrate the egg cell and release the genetic material contained in their heads. Once one has succeeded, rapid chemical changes prevent other sperm cells from entering the egg cell. Inside the egg cell, the sperm's genetic material (from a male) mixes with the genetic material carried by the egg (from a female). The fertilised egg can then develop through stages to form a new human baby, with a set of genes from both parents.