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How does alternation of generations work in plant life cycles?
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Plant
Grandidier's baobas (Adansonia grandidieri) in Madagascar.
In plants, the alternation of generations is a life cycle characterized by two distinct, multicellular phases that alternate with one another: the gametophyte and the sporophyte.12
The Two Phases
- Gametophyte (Haploid): This sexual phase consists of cells with a single set of chromosomes (). It produces gametes (sperm and eggs) through mitosis.12
- Sporophyte (Diploid): Following fertilization, where two gametes fuse to form a zygote, the organism enters the sporophyte phase. This asexual phase produces spores through meiosis, which then germinate to begin the gametophyte phase anew.132
Evolutionary Trends
The relative dominance of these phases varies by plant group. In primitive bryophytes, the gametophyte is the dominant, more conspicuous phase. Conversely, in vascular plants—including angiosperms and gymnosperms—the sporophyte has become the dominant generation, often reducing the gametophyte to a microscopic structure.145