PROFESSOR P.M. MOTTA ET AL / SCIENCE PHOTO LIBRARY PROFESSOR P.M. MOTTA ET AL / SCIENCE PHOTO LIBRARY
Fertilised "polyspermic" eggs. Coloured light micrograph of two human egg cells, 24 hours after multiple fertilisation. Two sperm have penetrated each cell, instead of one sperm, producing these abnormal zygotes. Inside each cell (blue) are 3 rounded pronuclei: two sperm pronuclei and one egg pronucleus. This will produce an embryo with an abnormal number of chromosomes. Each egg cell has a thick zona pellucida layer (yellow) around it; some sperm (black dots) are seen embedded in this layer. Remnant corona cumulus cells (red) are also seen which originally enclosed the egg in the ovary. Magnification: x190 at 5x7cm size.
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