1: Zygote development in diplontic organisms
In multicellular organisms with a diplontic life cycle, the diploid zygote formed from the haploid gametes undergo repeated mitotic divisions to give rise to the multicellular body.
2: Zygote development in haplo-diplontic organisms
In organisms with a haplo-diplontic life cycle, the zygote usually undergoes mitosis to give rise to the diploid sporophyte. The spore mother cells present the sporophytes undergo meiosis to produce haploid spores.
The haploid spores then give rise to the gametophyte, which then produces gametes.