The formation of gamete the fusion of male and female gametes to a zygote, and a period of growth and development that occurs at various time.
Within the life cycle, meiotic divisions take place, in which cell proceed from a diploid to a haploid stage;
In the diploid stage two homologous copies of each chromosome are present in the cells and in the haploid stage only one sample of each chromosome in present in each cell.
Gametes are always haploid, whereas zygotes are diploid.During the life cycle mitotic divisions occur.
Depending on the phylum to which the organism belongs, these mitotic divisions occur in the haploid, or diploid phase, or in both the haploid and diploid stages.