Fertilisation involves the fusion of one egg from the mother and one sperm from the father to create a new human being. The fertilised egg is therefore a single cell that contains genetic information, half of which comes from the mother and half from the father. On fertilisation this one cell becomes an embryo and so begins the process known as development.

Image © Wellcome Images

Fertilisation takes place 12-24 hours after an egg is released from the mother's ovary. Upon contact with the egg, the sperm releases substances that eat through the egg's protective outer coat. Although millions of sperm are released, only one is able to enter the egg. This triggers a reaction that blocks further sperm entry. Genetic information is contained in the head of the sperm. This fuses with the genetic material of the mother that is in the egg. Image © Wellcome Images

Look it up: How the sperm and egg meet Selected research papers: Update on human sperm Report of signals that control reproductive aging by regulating egg and germ-line quality Recent work on sperm penetration of the egg Key labs that work on fertility: Chris Barratt , University of Dundee Focuses on the physiological changes that take place in the sperm cell prior to interaction with an egg Lynn Fraser, Kings College London Focuses on the mechanisms that control mammalian sperm fertilizing ability University of Edinburgh centre for reproductive biology Focuses on pathologies of female and male reproductive tissues, infertility, contraception and hormone replacement therapy.

The 1000 sperm coat: Nylon, cotton This coat took 105 hours to embroider with nylon and cotton threads onto dissolvable fabric. It was soaked in cool water. The backing cloth fell away to reveal the fabric shown. Drawing 1997 Copyright Helen Storey