Reproduction
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Reproduction (or procreation or breeding) is the biological process by which new individual organisms – "offspring" – are produced from their "parent" or parents. Reproduction is a fundamental feature of all known life; each individual organism exists as the result of reproduction. There are two forms of reproduction: asexual and sexual.
In asexual reproduction, an organism can reproduce without the involvement of another organism. Asexual reproduction is not limited to single-celled organisms. The cloning of an organism is a form of asexual reproduction. By asexual reproduction, an organism creates a genetically similar or identical copy of itself. The evolution of sexual reproduction is a major puzzle for biologists. The two-fold cost of sexual reproduction is that only 50% of organisms reproduce[1] and organisms only pass on 50% of their genes.[2]
Sexual reproduction typically requires the sexual interaction of two specialized reproductive cells, called
. This produces offspring organisms whose genetic characteristics are derived from those of the two parental organisms.Asexual
Asexual reproduction is a process by which organisms create genetically similar or identical copies of themselves without the contribution of genetic material from another organism.
Some species that are capable of reproducing asexually, like hydra, yeast (See Mating of yeasts) and jellyfish, may also reproduce sexually. For instance, most plants are capable of vegetative reproduction—reproduction without seeds or spores—but can also reproduce sexually. Likewise, bacteria may exchange genetic information by conjugation.
Other ways of asexual reproduction include
Sexual
 | This section needs additional citations for verification. (August 2021) ) |
Sexual reproduction is a
. MostAllogamy
Allogamy is the fertilization of flowers through cross-pollination, this occurs when a flower's ovum is fertilized by spermatozoa from the pollen of a different plant's flower.[13][14] Pollen may be transferred through pollen vectors or abiotic carriers such as wind. Fertilization begins when the pollen is brought to a female gamete through the pollen tube. Allogamy is also known as cross fertilization, in contrast to autogamy or geitonogamy which are methods of self-fertilization.
Autogamy
Self-
Mitosis and meiosis
Mitosis The resultant number of cells in mitosis is twice the number of original cells. The number of
Meiosis The resultant number of cells is four times the number of original cells. This results in cells with half the number of
Same-sex
 | This section possibly contains original research. (April 2021) |
Scientific research is currently investigating the possibility of same-sex procreation, which would produce offspring with equal genetic contributions from either two females or two males.[16][17][18] The obvious approaches, subject to a growing amount of activity, are female sperm and male eggs. In 2004, by altering the function of a few genes involved with imprinting, other Japanese scientists combined two mouse eggs to produce daughter mice[19] and in 2018 Chinese scientists created 29 female mice from two female mice mothers but were unable to produce viable offspring from two father mice. Researches noted that there is little chance these techniques would be applied to humans in the near future.[20][21]
Strategies
There are a wide range of reproductive strategies employed by different species. Some animals, such as the
Other types
- Polycyclic animals reproduce intermittently throughout their lives.
- Semelparous organisms reproduce only once in their lifetime,[22] such as annual plants (including all grain crops), and certain species of salmon, spider, bamboo and century plant.[23] Often, they die shortly after reproduction. This is often associated with r-strategists.
- Iteroparous organisms produce offspring in successive (e.g. annual or seasonal) cycles, such as perennial plants. Iteroparous animals survive over multiple seasons (or periodic condition changes). This is more associated with K-strategists.
Asexual vs. sexual reproduction
Organisms that reproduce through asexual reproduction tend to grow in number exponentially. However, because they rely on mutation for variations in their DNA, all members of the species have similar vulnerabilities. Organisms that reproduce sexually yield a smaller number of offspring, but the large amount of variation in their genes makes them less susceptible to disease.
Many organisms can reproduce sexually as well as asexually. Aphids, slime molds, sea anemones, some species of starfish (by fragmentation), and many plants are examples. When environmental factors are favorable, asexual reproduction is employed to exploit suitable conditions for survival such as an abundant food supply, adequate shelter, favorable climate, disease, optimum pH or a proper mix of other lifestyle requirements. Populations of these organisms increase exponentially via asexual reproductive strategies to take full advantage of the rich supply resources.[24]
When food sources have been depleted, the climate becomes hostile, or individual survival is jeopardized by some other adverse change in living conditions, these organisms switch to sexual forms of reproduction. Sexual reproduction ensures a mixing of the gene pool of the species. The variations found in offspring of sexual reproduction allow some individuals to be better suited for survival and provide a mechanism for selective adaptation to occur. The meiosis stage of the sexual cycle also allows especially effective repair of DNA damages (see Meiosis).[24] In addition, sexual reproduction usually results in the formation of a life stage that is able to endure the conditions that threaten the offspring of an asexual parent. Thus, seeds, spores, eggs, pupae, cysts or other "over-wintering" stages of sexual reproduction ensure the survival during unfavorable times and the organism can "wait out" adverse situations until a swing back to suitability occurs.
Life without
The existence of life without reproduction is the subject of some speculation. The biological study of how the origin of life produced reproducing organisms from non-reproducing elements is called
Scientists have speculated about the possibility of creating life non-reproductively in the laboratory. Several scientists have succeeded in producing simple viruses from entirely non-living materials.[25] However, viruses are often regarded as not alive. Being nothing more than a bit of RNA or DNA in a protein capsule, they have no metabolism and can only replicate with the assistance of a hijacked cell's metabolic machinery.
The production of a truly living organism (e.g. a simple bacterium) with no ancestors would be a much more complex task, but may well be possible to some degree according to current biological knowledge. A
There is some debate within the scientific community over whether this cell can be considered completely synthetic[27] on the grounds that the chemically synthesized genome was an almost 1:1 copy of a naturally occurring genome and, the recipient cell was a naturally occurring bacterium. The Craig Venter Institute maintains the term "synthetic bacterial cell" but they also clarify "...we do not consider this to be "creating life from scratch" but rather we are creating new life out of already existing life using synthetic DNA".[28] Venter plans to patent his experimental cells, stating that "they are pretty clearly human inventions".[27] Its creators suggests that building 'synthetic life' would allow researchers to learn about life by building it, rather than by tearing it apart. They also propose to stretch the boundaries between life and machines until the two overlap to yield "truly programmable organisms".[29] Researchers involved stated that the creation of "true synthetic biochemical life" is relatively close in reach with current technology and cheap compared to the effort needed to place man on the Moon.[30]
Lottery principle
Sexual reproduction has many drawbacks, since it requires far more energy than asexual reproduction and diverts the organisms from other pursuits, and there is some argument about why so many species use it.
See also
- Breeding season
- Masting
- Mating system
- Modes of reproduction
- Plant reproduction
- Reproductive system
Notes
- ^ Ridley M (2004) Evolution, 3rd edition. Blackwell Publishing, p. 314.
- ^ John Maynard Smith The Evolution of Sex 1978.
- ISBN 978-0-920269-81-7.
- ISSN 0190-8286. Retrieved 2023-03-27.
- ^ Savage, Thomas F. (September 12, 2005). "A Guide to the Recognition of Parthenogenesis in Incubated Turkey Eggs". Oregon State University. Archived from the original on November 15, 2006. Retrieved 2006-10-11.
- ISBN 978-0-08-096156-9, archivedfrom the original on 2021-04-20, retrieved 2020-10-05
- ISBN 978-3-319-47829-6.
- PMID 27619696.
- JSTOR 984858.
- PMID 1628815.
- PMID 3324702.
- PMID 27619699.
- ^ "Allogamy". Biology Online. 7 October 2019. Archived from the original on 25 September 2021. Retrieved 20 August 2022.
- ^ ISBN 978-0128126288. Archivedfrom the original on 2022-08-20. Retrieved 2022-08-20.
- .
- ISBN 978-1-108-49858-6.
- ^ "Timeline of same-sex procreation scientific developments". samesexprocreation.com. Archived from the original on 2011-02-08. Retrieved 2008-01-31.
- S2CID 35387886.
- ^ "Japanese scientists produce mice without using sperm". The Washington Post. Sarasota Herald-Tribune. April 22, 2004. Archived from the original on July 23, 2021. Retrieved November 19, 2020.
- from the original on 2018-10-12. Retrieved 2018-10-12.
- PMID 30318303.
- from the original on 2022-08-31. Retrieved 2022-08-20.
- ^
Young, Truman P.; Carol K. Augspurger (1991). "Ecology and evolution of long-lived semelparous plants". Trends in Ecology and Evolution. 6 (9): 285–289. PMID 21232483.
- ^ S2CID 218971234.
- S2CID 5810309.
- PMID 20488990.
- ^ a b Robert Lee Hotz (May 21, 2010). "Scientists Create First Synthetic Cell". The Wall Street Journal. Archived from the original on January 29, 2015. Retrieved April 13, 2012.
- ^ Craig Venter Institute. "FAQ". Archived from the original on 2010-12-28. Retrieved 2011-04-24.
- ^ W. Wayte Gibbs (May 2004). "Synthetic Life". Scientific American. Archived from the original on 2012-10-13. Retrieved 2012-12-22.
- ^ "NOVA: Artificial life". PBS. Archived from the original on 2007-01-21. Retrieved 2007-01-19.
- Williams G. C.1975. Sex and Evolution. Princeton (NJ): Princeton University Press.
- PMID 24617324.
References
- Tobler, M. & Schlupp, I. (2005) Parasites in sexual and asexual mollies (Poecilia, Poeciliidae, Teleostei): a case for the Red Queen? Biol. Lett. 1 (2): 166–168.
- Parasite Rex: Inside the Bizarre World of Nature's Most Dangerous Creatures, New York: Touchstone, 2001.
- "Allogamy, cross-fertilization, cross-pollination, hybridization". GardenWeb Glossary of Botanical Terms (2.1 ed.). 2002.
- "Allogamy". Stedman's Online Medical Dictionary (27 ed.). 2004.
Further reading
- Judson, Olivia (2003). ISBN 978-0-09-928375-1
- Richard E. Michod and Bruce E. Levin, editors (1987). The Evolution of Sex: An Examination of Current Ideas. Sinauer Associates Inc., Publishers, Sunderland, MA
- Michod, R.E. (1994). Eros and Evolution: A natural philosophy of sex. Addison-Wesley Publishing Company, Reading, MA
External links
- Asexual Reproduction Archived 2018-01-22 at the Wayback Machine
- Journal of Biology of Reproduction
- Journal of Andrology Archived 2005-11-07 at the Wayback Machine
- . Encyclopædia Britannica (11th ed.). 1911.
- "Replication and Reproduction." Stanford Encyclopedia of Philosophy
