Haploid organisms produce their gametes by mitotic divisions. Since their genetic material is composed of only one set of chromosomes (uniparental), they cannot divide by the means of meiosis. Mitosis maintains the number of chromosomes similar to the parental genetic makeup while meiosis produces half of the number of parental chromosomes in the progeny. From the evolutionary point of view, meiosis is important because the variations can come after this kind of cell division. In mitosis, a simple division of the nucleus takes place without the formation of chromosomes.
For example, lower organisms like amoeba, bacteria, etc.