Ulothrix is a heterothallic algae. Its sexual reproduction is isogamous in nature. Its sex is described.
1. Gamete formation: Any cell without Ulothrix’s hold fast in unfavorable environment develops into gametangium. The protoplast of the gametangium divides by mitosis to produce 8, 16, 32 or 64 daughter protoplasts. Each fertilized protoplast develops into a biflagellate (two-flagellated) gamete. They are denoted as + and – strains for being heterogeneous in nature.
2. Gamete emerson : Gametes are enclosed by vesicles. They emerge from the gametangium enclosed in vesicles. The vesicle then breaks down and the gametes swim freely.
3. Fertilization: Fertilization of + strain and – strain from different filaments takes place. Fertilization results in the formation of a zygote.
4. Resting spore: The zygote of Ulothrix has four flagella. It is active for some time. Later the flagella is lost and the wall becomes a resting spore.
5. Germination: After resting, the nucleus of the zygote divides by meiosis to form immature protoplasts with 4-16 haploid nuclei. They have half +strain and half -strain properties. Each aborted protoplast develops into a flagellated spore. They are called meiospores as they are produced by the process of meiosis. Zoospores and aplanospores germinate under favorable conditions to form new filaments of Ulothrix.