Meiosis
In parthenogenesis, the eggs contain only the mother's genetic material, and they are not fertilized. The egg cells may be produced either by meiosis or mitosis. When meiosis occurs, crossing-over produces a genetic fingerprint which differs somewhat from the mother's. So, the parthenogenetic greenfly offspring are not identical, and do show some genetic variation: some chromosome segments differ because of meiosis. Mitosis would produce identical offspring.