Alternation of generations is a reproductive cycle found in many plants, algae, and some fungi. It involves two distinct phases: the gametophyte stage, which is haploid (having one set of chromosomes) and produces gametes (sperm and eggs), and the sporophyte stage, which is diploid (having two sets of chromosomes) and produces spores through meiosis. In this cycle, the gametes fuse during fertilization to form a diploid zygote, which develops into the sporophyte. The sporophyte then undergoes meiosis to produce haploid spores, which grow into new gametophytes, continuing the cycle.