Variations on parthenogenesis. (a) Schematic representations of forms of non-meiotic reproduction. Starting genomes in this illustration are shown as maternal diploid (AB) or triploid (ABB) and paternal diploid (MM). True parthenogenesis does not require any intervention by sperm; diploid oocytes develop directly into diploid offspring of identical genotype to the mother. Hybridogenesis and gynogenesis involve the intervention of sperm. In hybridogenesis, a haploid oocyte is produced without meiosis and is fertilized by a sperm, which contributes its genome (M) to the offspring. However, the M genome is lost when oocytes are produced in the next generation, so the oocyte always contains an unchanged maternal genome. In gynogenesis, stimulation by sperm is required for the oocyte to develop into an embryo, but the sperm does not contribute any of its genetic material to the offspring. (b) Ways in which 'paternal' DNA can leak into gynogens. From left to right: small pieces of chromosomes from the sperm can be retained in the oocyte as microchromosomes (μ); a full sperm M haploid genome can be added, leading to polyploidization; all or part of a maternal genome can be replaced by the sperm M genome (kleptogenesis).