Diagrams of sperm and egg
Sperm must break through the protective coating of the egg to fertilize it and produce viable offspring.
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Annotation of diagrams of mature sperm and egg to indicate functions.
Eggs and sperm
Description:Fertilisation The oocyte is normally fertilised in the fallopian tubes, and by the time it reaches the uterus, 5 days later, it has already formed a blastocyst see embryogenesis Although many sperm can reach the egg, and bind to it, normally ony one sperm fuses with the plasma membrane of the egg, and injects its nucleus. The surface of the egg is covered with fine microvilli, which interact with the sperm, by clustering, and elongating to hold the sperm firmly in position. A protein called fertilin is important in the subsequent fusion of the egg and sperm plasma membranes, but the exact mechanism is still unclear. However, this results in extra mitotic spindles, and faulty segregation of chromosomes, nondiploid cells, and development usually stops. When the first sperm fuses, there is a rapid depolarisation of the egg, that initially blocks entry of further sperm. This also causes the levels of calcium ions to increase, which initiate the cortical reaction.