Fertilization and Development

• Fertilization is the process by which the two gametes from the parents fuse their genetic material to form a new individual (zygote). • Fertilization requires that sperm cells swimming through the uterine tube contact a secondary oocyte. • Once sperm penetrate the secondary oocyte's corona radiata, they enter the area of the zona pellucida. • A glycoprotein in the zona pellucida binds to sperm and triggers the release of digesting enzymes. • These enzymes help to digest a path for the sperm to reach the plasma membrane of the secondary oocyte. • The first sperm to penetrate the entire zona pellucida fuses with the secondary oocyte (syngamy). • Polyspermy is prevented by changes in the membrane of the secondary oocyte triggered by syngamy. • After a sperm penetrates the cell, the secondary oocyte completes meiosis II. • The oocyte subsequently divides into a larger ovum and a smaller secondary polar body that fragments and degenerates. • The fertilized ovum is now called a zygote, the first embryonic stage.

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