Final answer:
Fertilization is the fusion of sperm and egg to form a zygote, a process that can also be conducted outside the body via in vitro fertilization (I.V.F.) for those with infertility challenges.
Step-by-step explanation:
Fertilization is a crucial biological process in which a sperm and an egg fuse to create a zygote, the first cell of a new organism. This event ensures the necessary genetic material is combined to develop into an embryo and, later, a fully formed infant. In vitro fertilization (I.V.F.) is a specialized procedure wherein fertilization occurs outside the human body, typically in a lab using specialized culture dishes. This process is particularly significant for couples facing infertility challenges. I.V.F. involves the attachment of the sperm to the zona pellucida, triggering the acrosomal reactions, which allow the sperm to penetrate the protective glycoprotein matrix and fuse its nucleus with the egg's, establishing the zygote with a complete diploid set of chromosomes.