It a haplont. After fertilization the zygote soon goes through meiosis and produces four haploid flagellated spores (zoo-meiospores), which develop to haploid unicellular individuals. Sometimes, spores are formed from the meiotic products through an additional mitotic division (formation of zoomitospores). This is a type of vegetative propagation. Further, the haploid individuals can go through a mitotic step and become gametes. Gametes fuse (syngamie) together on their turn to form a diploid zygote. The zygote can go to quiescence; it is then called a cystozygote.
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Haploid vegetative cells (V) perform asexual reproduction under optimal growth conditions. They turn into pregametes (pG) under nitrogen deprivation conditions in darkness. Light induces the formation of gametes (G). Gametes may lose their mating ability and turn to dark-inactivated gametes (dG) upon dark treatment. For simplicity, only the conversion of the plus strain is shown. When gametes of two different mating types are mixed, they will mate and fuse to a quadriflagellated cell that is called early zygote (eZ). The early zygotes convert to mature zygotes (Z) having a thick cell wall after exposure to 15-18 h light followed by 5 days in the dark (Jiang and Stern, 2009). In the absence of any light, zygotes will stay as dormant cells; when light and nitrogen are available, they will undergo meiosis and germinate into four vegetative cells, two plus and two minus.
