Diplontic, Haplontic & Haplodiplontic Life Cycles

Diplontic Life Cycle

• Characterized by gametic meiosis, where zygotes undergo mitosis to form multicellular diploid organisms.
• Diploid individuals produce haploid gametes via meiosis; haploid phase is less prominent.
• Gametes (haploid, n) are typically the only haploid cells in the cycle.
• Organisms mainly include animals and some algae.

Haplontic Life Cycle

• Zygotic meiosis occurs immediately after the fusion of two cell nuclei (karyogamy).
• Produces several haploid cells after the diploid phase ends, which can divide mitotically.
• The cycle features zygotes as the sole diploid cells, with mitosis occurring in haploid individuals.
• Examples include most fungi and some algae, such as Volvox and dinoflagellates.
• Organisms thrive in dark, wet environments to avoid the harmful effects of ultraviolet light.

Life Cycle Characteristics

• Haplontic organisms primarily exist in a multicellular haploid form.
• Gametes are produced through mitosis, leading to a multicellular haploid stage before fertilization occurs.
• Upon fertilization, a unicellular diploid zygote is formed, initiating the diploid phase.

Key Processes

• In the Diplontic cycle, the zygote undergoes mitosis producing a multicellular diploid organism.
• In the Haplontic cycle, after meiosis, mitosis creates multicellular haploid organisms.
• Fertilization in both cycles leads to the formation of the zygote, but the duration and characteristics of the diploid phase differ markedly.