The term for the union of two dissimilar sexual cells or gametes to form a new individual is called fertilization. Fertilization is a crucial process in sexual reproduction where the male gamete, typically a sperm cell, and the female gamete, typically an egg cell, combine to create a zygote. This zygote then develops into a new individual with a unique set of genetic traits.

During fertilization, the sperm cell must first penetrate the protective layer surrounding the egg cell, known as the zona pellucida. Once inside, the sperm releases enzymes to help break down this barrier and reach the egg's plasma membrane. The plasma membranes of the sperm and egg then fuse together, allowing the genetic material from both cells to combine.

After fertilization occurs, the zygote undergoes a series of cell divisions and transformations to develop into a multicellular organism. This process is known as embryogenesis and is essential for the growth and development of the new individual. The zygote will continue to divide and differentiate into various cell types, eventually forming tissues, organs, and ultimately a fully formed organism.

There are two main types of fertilization: external fertilization and internal fertilization. External fertilization occurs outside of the body in aquatic environments, where both sperm and egg are released into the water and come into contact to form a zygote. Internal fertilization, on the other hand, occurs inside the female reproductive tract, providing a more protected environment for the developing zygote.

Overall, fertilization is a complex and intricate process that is essential for the continuation of a species. It ensures genetic diversity and variability among individuals, allowing for adaptation and evolution over time. Without fertilization, the creation of new life would not be possible, making it a fundamental aspect of sexual reproduction in organisms.

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