How can only one sperm fertilize an egg

For more information, visit the cookies page. Evolution likely accounts for the high sperm count in a typical ejaculate — a male who is able to produce more sperm obviously has a better likelihood of fertilizing a female than his competitors. John MacLeod and Ruth Gold provided an early indication of a downside to high sperm counts in a paper. Both induce morphologic and biochemical changes in the acrosomal region of the spermatozoa. The other sperm die within 48 hours.
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InVia Fertility Specialists Blog

As the baby grows, the uterus stretches until it's about the size of a basketball. During cortical rotation movements, the dense, yolky vegetal deep cytoplasm rotates with respect to the overlying cortex to produce a 30 degree relative rotation. For Bergman and Casadevall, this benefit even explains what tipped Darwin's scales in favor of mammals, allowing them to edge out other vertebrates for dominance after the Cretaceous-Tertiary mass extinction wiped out the dinosaurs. The molecular mechanisms are less well understood than those of sea urchins. A mechanical "sperm sorter" that Magnified image of a human sperm penetrating a female egg ovum. Seriously though, the short and sweet answer is this:
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A New Kind of Twin - TIME

Content on this website is from high-quality, licensed material originally published in print form. The eggs of marine invertebrates, especially echinoderms , are classical objects for the study of fertilization. Cortical granules are formed in a cell component known as a Golgi complex , from which they migrate to the surface of the maturing egg. Only afterwards do special mechanisms make sure that just one set of male chromosomes contributes to the offspring. Through fertilization , the egg and sperm are saved: In mouse sperm, a transmembrane protein called fertilin, which becomes exposed on the sperm surface during the acrosome reaction , helps the sperm bind to the egg plasma membrane and may also have a role in the fusion of the two plasma membranes.
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In such cases the polyspermy-preventing reaction resides in the egg surface. Once fertilized, the egg is called a zygote. Once the spermatozoa have penetrated the oocyte's cytoplasm, the head of the spermatozoa separates from the tail, leaving the tail behind. Molecular Biology of the Cell. At this point, only a few sperm are still in the competition, as the vast majority got lost somewhere along the way. When polyspermy occurs, multipolar or extra miotic spindles form, which stop the development of the fertilized egg by causing faulty segregation of chromosomes during cell division. Yet their work remains highly relevant for the continued progress of this field.
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