Produced by fusion, the zygote is reduced to half after fertilization. Fusion of the micro- and macrogametes in the mosquito stomach doubles the chromosome set in the fused karyosome or zygote that becomes sporozoites. Plasmodium is a haplont, or haploid organism as the entire life cycle is except for fertilization that has one set of chromosomes each from the micro- and macrogamete.. Meiosis is fusion then reduction. Haploid gametes fuse to immediately reduce. Why do certain merozoites convert to gametes in the vertebrate host?