HENNING DALHOFF / SCIENCE PHOTO LIBRARY HENNING DALHOFF / SCIENCE PHOTO LIBRARY
DNA in sperm and ovum cells, illustration. The sperm cell (top), the male sex cell, is composed of a head, a body and a tail. Its head consists of an acrosome, a cap-like structure that breaks down the barrier around the female sex cell (ovum, bottom). The nucleus of both sex cells (gametes) contains the cells' genetic information (deoxyribonucleic acid, DNA, shown in red). During fertilisation, sperm cells release chemicals to penetrate the ovum's outer layers. This allows the genetic material in the sperm's head to fuse with the egg's DNA to form a zygote. The egg then forms a barrier to other sperm.
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