It's called parthenogenesis.
Parthenogenesis (PG) is a form of asexual reproduction where an embryo develops from an unfertilized egg cell. The word "parthenogenesis" comes from the Greek words "parthenos," meaning virgin, and "genesis," meaning creation. It's essentially "virgin birth."
How Parthenogenesis Works
Typically, sexual reproduction involves the fusion of a sperm cell and an egg cell, each contributing half the genetic material needed for a complete organism. In parthenogenesis, this doesn't happen. Instead, the egg cell develops into an embryo without fertilization.
Types of Parthenogenesis
There are different types of parthenogenesis, broadly categorized as:
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Obligate Parthenogenesis: This is the only method of reproduction for the species. These organisms rely entirely on parthenogenesis for reproduction.
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Facultative Parthenogenesis: This occurs when a species can reproduce both sexually and asexually (via parthenogenesis). The trigger for switching between reproduction methods may be environmental stressors or a lack of available mates.
Examples of Parthenogenesis
While parthenogenesis is more common in invertebrates (e.g., insects, crustaceans), it has been observed in some vertebrates, including:
- Insects: Aphids, bees, and wasps
- Crustaceans: Some species of crayfish
- Fish: Some species of sharks and bony fish
- Amphibians: Some salamanders
- Reptiles: Some lizards and snakes
- Birds: While rare, parthenogenesis has been documented in domesticated turkeys and chickens.
Parthenogenesis in Mammals (including Humans)
Natural, sustained parthenogenesis has not been observed in mammals. This is largely due to a process called genomic imprinting, where certain genes are expressed differently depending on whether they are inherited from the mother or the father. Successful mammalian development requires contributions from both parents to balance these imprinted genes.
However, scientists have been able to induce parthenogenesis in mammalian eggs in laboratory settings. While these embryos haven't been able to develop to term, these studies provide valuable insights into reproductive biology.
Significance
Parthenogenesis offers several advantages for organisms that utilize it:
- Rapid Reproduction: It allows females to reproduce quickly without needing a mate.
- Colonization: A single female can colonize a new habitat.
- Preservation of Favorable Traits: The offspring are usually clones of the mother, so beneficial traits are passed on unchanged.
Despite these advantages, the lack of genetic diversity in parthenogenetic populations can make them more vulnerable to environmental changes and diseases.
