Asexual reproduction is a mode of reproduction where an offspring is created from a single parent. Many forms of bacteria are able to reproduce without a mate. The ability to reproduce without a mate is relatively rare in multicellular organisms, particularly animals. Some animals are able to alternate, reproducing both sexually and asexually. Parthenogenesis is a form of asexual reproduction.

Sharks

• The most surprising and developed animal that can reproduce without a mate is the shark. In certain cases, female sharks are able to reproduce asexually through a process known as parthenogenesis. This is the first case of asexual reproduction in an ancient vertebrate species. Scientists discovered the rare capability when a female shark gave birth at a zoo in a tank that held three adult female hammerhead sharks but no males. The baby shark's DNA matched perfectly with its mother's.

Reptiles

• Most reptiles reproduce sexually, but parthenogenesis does appear to occur naturally in certain species. Whiptails and rock lizards are believed to reproduce asexually at times. Geckos only reproduce through parthenogenesis; no remaining males have been found. Likewise, blindsnakes only reproduce asexually and the only specimens collected have been female. The Komodo dragon and boa constrictors both normally reproduce sexually, but there have been some documented cases where they have reproduced asexually.

Birds

• Chickens can reproduce using parthenogenesis, though the development usually stops long before the embryo reaches full term. There have been isolated cases of parthenogen chickens being born but it is rare. Turkeys also can reproduce without a mate. A female turkey can produce fertile eggs in the absence of a male. The result, however, is nearly always a male and often sickly. This asexual reproduction in turkeys is rare.

Insects

• Certain species of bees are able to reproduce without a mate. Small carpenter bees and parasitic wasps are parthenogenetic. Some species of ants from Central and South America can reproduce asexually. In one type of European ant colony, only the queen is able to reproduce without a mate. Some types of crayfish and water fleas alternate from sexual to asexual reproduction. Snails and flatworms also can reproduce asexually. Parthenogenesis occurs naturally in many other invertebrates and plants.