Final answer:
Mammalian fertilization involves sperm penetrating the egg's protective layers, initiating an acrosomal reaction and fusing with the egg's membrane to transfer the haploid nucleus, leading to the formation of a diploid zygote, while a cortical reaction prevents further sperm entry.
Step-by-step explanation:
Mammalian sperm-egg recognition and fusion is a complex process ensuring that only one sperm fuses with an egg to form a zygote. The egg is encapsulated by the zona pellucida, a layer rich in glycoproteins. Sperm undergo an acrosomal reaction, where digestive enzymes from the acrosome degrade the zona pellucida, allowing the sperm to bind to receptors and ultimately fuse with the egg plasma membrane. This leads to the transfer of the sperm nucleus into the ovum, and the formation of a diploid genome from the two haploid nuclei.
The initial contact of the sperm with the corona radiata attracts the sperm using chemical signals, followed by penetration through the zona pellucida. Specific receptors on the oocyte are crucial for the binding of sperm, triggering the fusion of their membranes. The completion of this process is marked by the oocyte's membrane restructuring to prevent further sperm entry, ensuring monospermy.
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