PROF. P. MOTTA / DEPT. OF ANATOMY / UNIVERSITY "LA SAPIENZA", ROME / SCIENCE PHOTO LIBRARY PROF. P. MOTTA / DEPT. OF ANATOMY / UNIVERSITY "LA SAPIENZA", ROME / SCIENCE PHOTO LIBRARY
Fertilisation. False-colour scanning electron micrograph of sperm (blue) on a human egg. In order to fertilise the egg a spermatozoon must penetrate the thick layer of follicular cells (pink), called the corona radiata, and the inner membrane known as zona pellucida (not seen here). The penetration occurs thanks to special enzymes released by the sperm's head. Once a spermatozoon ruptures the zona pellucida a chemical reaction strenghtens the two membranes. This prevents the entrance of other sperm, avoiding the creation of embryos with more than 46 chromosomes. Magnification: x910 at 6x7cm size. Magnification: x1405 at 4x5inch size.
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