EDELMANN / SCIENCE PHOTO LIBRARY EDELMANN / SCIENCE PHOTO LIBRARY
Light micrograph showing the fusion of male and female human pronuclei - the actual moment of fertilisation following the successful pentetration of the ovum by a single sperm. The pronuclei appear as the two small circles which are merging in the centre of the oocyte. When they have merged the newly formed nucleus will contain the full complement of 46 human chromosomes, 23 from each parent.
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