Zygotic meiosis is the one that occurs in the haplontic haplobiontic life cycle. Gametes from adult haploid individuals unite forming the diploid zygote. The zygote undergoes meiosis and generates four haploid cells that by mitosis develop into adult individuals. Therefore in the zygotic meiosis the cell that undergoes meiosis is the zygote and the gametes are formed by mitosis.
Gametic meiosis is that in which meiosis produces gametes, i.e., haploid cells that each of which can unite with another gamete forming the zygote. It occurs in the diplontic haplobiontic life cycle (e.g., in humans) in which the individual is diploid and meiosis forms gametes.
Sporic meiosis happens in metagenesis (alternation of generations, or diplobiontic life cycle). In this life cycle cells from the diploid individual (called sporophyte) undergo meiosis producing haploid spores that do not unite with others but instead develop by mitosis into haploid individuals (called gametophytes). In this life cycle the gametes are made by mitosis from cells of the gametophyte.
