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Hot, Steamy Asexual Reproduction
Reproduction usually follows the same basic blueprint: Boy meets girl; sperm meets egg; congratulations, you have a baby.
Sometimes, though, there’s no boy and there’s no sperm. There’s just a girl, an egg and eventually a baby. This virgin birth is called parthenogenesis (from Greek, meaning “virgin creation”), and it happens when an embryo develops by itself without fertilization of an ovum (egg cell). The resulting baby is called a parthenogen, and because it results from the inheritance of only a single sex chromosome from the mother, it will always be female in animals where two like chromosomes determine the female sex (the XY sex-determination system), and always male in animals where two like chromosomes make for a male (the ZW sex-determination system, where WZ is female, ZZ is male and WW is inviable).
Scientists have found a number of animals that can reproduce this way, and have also figured out how to induce other animals to perform the trick. Some researchers have even tried to make it happen in humans.
Some Examples:
In insects, parthenogenesis is common among
honeybees. In a hive of domesticated honeybees, the queen bee is the only fertile female, but the female worker bees, through parthenogenesis, produce male drones to mate with the queen. Additionally, some parasitic bacteria can induce parthenogenesis in insects.
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Marmorkrebs, a type of crayfish discovered only a decade ago, produce parthenogens that are genetically identical to their mother.
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Fifteen species of
whiptail lizard found in the American Southwest reproduce exclusively by parthenogenesis (populations are all female), but still exhibit mating behavior (including one female mounting another that is about to lay eggs) because the sexual behavioral stimulates maximum reproductive success.
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The
Komodo dragon, the sex of which is determined by the WZ system, has been observed to switch to sexual reproduction after parthenogenetic reproduction. Scientists think this helps the lizard colonize islands.
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Several cases of parthenogenesis have been documented in
sharks. In each case, pups were born in aquarium tanks that contained only female sharks. The parthenogenetic reproductions concern shark experts and conservationists because, while the population increases, genetic diversity decreases. Additionally, sharks have an XY sex-determination system, so female populations can only produce more females.
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While there are no known cases of parthenogenesis occurring naturally in mammals in the wild, scientists have successfully induced it in rabbits, mice and monkeys. The resulting embryos ran into problems, however, because of biological phenomenon in mammals (and some flowering plants) known as genomic imprinting. During the formation of sperm and egg cells, certain genes necessary for embryo development are shut down by chemical marks, or imprints. Some of these imprints are in sperm, others are in the egg. All the key genes are there only when a sperm and an egg meet, so without paternally imprinted genes, a mammalian embryo created by parthenogenesis develops abnormally.
Read the full text here: http://www.mentalfloss.com/blogs/archives/21066#ixzz2CkmAoEu9 --brought to you by mental_floss!
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