Parthenogenesis is a form of reproduction in which an egg can develop into an embryo without being fertilized by a sperm. It occurs commonly among lower plants and invertebrate animals (particularly rotifers, aphids, ants, wasps, and bees) and rarely among higher vertebrates. The egg cell can be haploid (n) to produce, for example, male honeybees (drones) or diploid (2n) as produced in wingless female aphids which, during the summer months, produce diploid eggs by mitosis that develop into female adults, only forming haploid gametes by meiosis in the autumn prior to normal sexual reproduction. In some species of aphid, males are absent or very rare. Parthenogenesis is the normal means of reproduction in a few plants (for example, dandelions).
