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How do haploid and diploid stages alternate in algal life cycles?
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Algae
The macroscopic genus of algae known as Acetabularia is commonly called “mermaid's wine glass” because of the distinctive umbrella-like shape of the tips of its stalks.
In sexually reproducing algae, the life cycle typically alternates between a haploid phase and a diploid phase, a process known as alternation of generations.12
- Haploid Phase (Gametophyte): Cells in this stage contain a single set of chromosomes. The gametophyte produces gametes through mitosis. When two haploid gametes fuse during fertilization, they form a diploid zygote.13
- Diploid Phase (Sporophyte): The zygote develops into the diploid sporophyte, which contains two sets of chromosomes. Through the process of meiosis, the sporophyte produces haploid spores. These spores eventually germinate to develop into a new haploid gametophyte, completing the cycle.13
The dominance of these stages varies by species; in some, the sporophyte is dominant, while in others, the gametophyte is the primary phase. Some algae, such as Ectocarpus, exhibit alternating vegetative stages, while others, like Spirogyra, exist primarily in a haploid state with the zygote serving as the only diploid cell. Environmental factors often regulate the transition between these phases.132