Plant Diversity

Botany Basics

What is the alternation of generations in plants?

All plants’ sexual life cycles are characterized by something called the Alternation of Generations (capitalized or not), which means the generations essentially alternate between what are called diploid sporophytes and haploid gametophytes. Sporophytes (often represented as 2n) produce haploid spores as a result of meiosis; the spores grow into multicellular, haploid individuals known as gametophytes (often represented as n). Spores are the first cells of the gametophyte generation, and gametophytes produce gametes as a result of mitosis. Male and female gametes fuse to form a zygote, which grows into a sporophyte, with the zygote being the first cell of the following sporophyte generation. Thus, the life cycle of the plant is complete. (For more about meiosis and mitosis, see the chapter “Cellular Basics.”)

This diagram illustrates the Alternation of Generations in plants in which a a generation of diploid sporophytes is followed by one of haploid gametophytes.


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