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Ejaculated human sperm look like tiny 'tadpole' structures under a microscope. They are not visible by the human eye. Each sperm cell consists of a head and tail structure. Within the head region is a structure called a nucleus which contains 23 tightly packed chromosomes that carry all the man's genetic material. The tail structure allows the sperm to actively move and penetrate the egg.
When the sperm and egg join (fuse) in a process called fertilisation, each contribute half of the required chromosomes to produce a zygote with a total of 46 chromosomes, including the sex chromosomes (the normal complement of genetic material). The zygote then goes on to form the developing foetus. Fertilisation can be achieved either by sexual intercourse between a male and a female, or by Assisted Reproductive Technologies such as in vitro fertilisation (IVF).
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