PROFESSOR P.M. MOTTA ET AL / SCIENCE PHOTO LIBRARY PROFESSOR P.M. MOTTA ET AL / SCIENCE PHOTO LIBRARY
Fertilised egg. Coloured light micrograph of a human egg cell 4 hours after fertilisation. The egg cell is coloured pink. Inside it are two rounded pronuclei (orange), one comes from the egg and the other from the sperm. When they fuse, the egg becomes a zygote containing the full 46 human chromosomes. Around the egg is a thick zona pellucida layer (yellow); sperm can be seen (black dots) embedded in this layer. Remnant corona cumulus cells (blue) are also seen which originally enclosed the egg in the ovary. This egg will soon begin its first cell division. Magnification: x150 at 6x7cm size.
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