Biological life cycle

In biology, a biological life cycle (or just life cycle when the biological context is clear) is a series of changes in form that an organism undergoes, returning to the starting state. "The concept is closely related to those of the life history, development and ontogeny, but differs from them in stressing renewal."[1] Transitions of form may involve growth, asexual reproduction, or sexual reproduction.

In some organisms, different "generations" of the species succeed each other during the life cycle. For plants and many algae, there are two multicellular stages, and the life cycle is referred to as alternation of generations. The term life history is often used, particularly for organisms such as the red algae which have three multicellular stages (or more), rather than two.[2]

Life cycles that include sexual reproduction involve alternating haploid (n) and diploid (2n) stages, i.e., a change of ploidy is involved. To return from a diploid stage to a haploid stage, meiosis must occur. In regard to changes of ploidy, there are 3 types of cycles:

  • haplontic life cycle — the haploid stage is multicellular and the diploid stage is a single cell, meiosis is "zygotic".
  • diplontic life cycle — the diploid stage is multicellular and haploid gametes are formed, meiosis is "gametic".
  • haplodiplontic life cycle (also referred to as diplohaplontic, diplobiontic, or dibiontic life cycle) — multicellular diploid and haploid stages occur, meiosis is "sporic".

The cycles differ in when mitosis (growth) occurs. Zygotic meiosis and gametic meiosis have one mitotic stage: mitosis occurs during the n phase in zygotic meiosis and during the 2n phase in gametic meiosis. Therefore, zygotic and gametic meiosis are collectively termed haplobiontic (single mitotic phase, not to be confused with haplontic). Sporic meiosis, on the other hand, has mitosis in two stages, both the diploid and haploid stages, termed diplobiontic (not to be confused with diplontic).

Culex mosquito life cycle en
Life cycle of a mosquito. An adult (imago) lays eggs which develop through several stages to adulthood. Reproduction completes and perpetuates the cycle.
Babesia life cycle human en
Life cycle of the single-celled parasite Babesia.


The study of reproduction and development in organisms was carried out by many botanists and zoologists.

Wilhelm Hofmeister demonstrated that alternation of generations is a feature that unites plants, and published this result in 1851 (see plant sexuality).

Some terms (haplobiont and diplobiont) used for the description of life cycles were proposed initially for algae by Nils Svedelius, and then became used for other organisms.[3][4] Other terms (autogamy and gamontogamy) used in protist life cycles were introduced by Karl Gottlieb Grell.[5] The description of the complex life cycles of various organisms contributed to the disproof of the ideas of spontaneous generation in the 1840s and 1850s.[6]

Haplontic life cycle

Haploid English
Zygotic meiosis

A zygotic meiosis is a meiosis of a zygote immediately after karyogamy, which is the fusion of two cell nuclei. This way, the organism ends its diploid phase and produces several haploid cells. These cells divide mitotically to form either larger, multicellular individuals, or more haploid cells. Two opposite types of gametes (e.g., male and female) from these individuals or cells fuse to become a zygote.

In the whole cycle, zygotes are the only diploid cell; mitosis occurs only in the haploid phase.

The individuals or cells as a result of mitosis are haplonts, hence this life cycle is also called haplontic life cycle. Haplonts are:

Diplontic life cycle

Diploid English
Gametic meiosis

In gametic meiosis, instead of immediately dividing meiotically to produce haploid cells, the zygote divides mitotically to produce a multicellular diploid individual or a group of more unicellular diploid cells. Cells from the diploid individuals then undergo meiosis to produce haploid cells or gametes. Haploid cells may divide again (by mitosis) to form more haploid cells, as in many yeasts, but the haploid phase is not the predominant life cycle phase. In most diplonts, mitosis occurs only in the diploid phase, i.e. gametes usually form quickly and fuse to produce diploid zygotes.

In the whole cycle, gametes are usually the only haploid cells, and mitosis usually occurs only in the diploid phase.

The diploid multicellular individual is a diplont, hence a gametic meiosis is also called a diplontic life cycle. Diplonts are:

Haplodiplontic life cycle

Diplohaplontic English
Sporic meiosis

In sporic meiosis (also commonly known as intermediary meiosis), the zygote divides mitotically to produce a multicellular diploid sporophyte. The sporophyte creates spores via meiosis which also then divide mitotically producing haploid individuals called gametophytes. The gametophytes produce gametes via mitosis. In some plants the gametophyte is not only small-sized but also short-lived; in other plants and many algae, the gametophyte is the "dominant" stage of the life cycle.

Haplodiplonts are:

Some animals have a sex-determination system called haplodiploid, but this is not related to the haplodiplontic life cycle.

Vegetative meiosis

Some red algae (such as Bonnemaisonia[16] and Lemanea) and green algae (such as Prasiola) have vegetative meiosis, also called somatic meiosis, which is a rare phenomenon.[17] Vegetative meiosis can occur in haplodiplontic and also in diplontic life cycles. The gametophytes remain attached to and part of the sporophyte. Vegetative (non-reproductive) diploid cells undergo meiosis, generating vegetative haploid cells. These undergo many mitosis, and produces gametes.

A different phenomenon, called vegetative diploidization, a type of apomixis, occurs in some brown algae (e.g., Elachista stellaris).[18] Cells in a haploid part of the plant spontaneously duplicate their chromosomes to produce diploid tissue.

Parasitic life cycle

Parasites depend on the exploitation of one or more hosts. Those that must infect more than one host species to complete their life cycles are said to have complex or indirect life cycles, while those that infect a single species have direct life cycles.

If a parasite has to infect a given host in order to complete its life cycle, then it is said to be an obligate parasite of that host; sometimes, infection is facultative—the parasite can survive and complete its life cycle without infecting that particular host species. Parasites sometimes infect hosts in which they cannot complete their life cycles; these are accidental hosts.

A host in which parasites reproduce sexually is known as the definitive, final or primary host. In intermediate hosts, parasites either do not reproduce or do so asexually, but the parasite always develops to a new stage in this type of host. In some cases a parasite will infect a host, but not undergo any development, these hosts are known as paratenic[19] or transport hosts. The paratenic host can be useful in raising the chance that the parasite will be transmitted to the definitive host. For example, the cat lungworm (Aelurostrongylus abstrusus) uses a slug or snail as an intermediate host; the first stage larva enters the mollusk and develops to the third stage larva, which is infectious to the definitive host—the cat. If a mouse eats the slug, the third stage larva will enter the mouse's tissues, but will not undergo any development.

Babesia life cycle human en
Life cycle of the apicomplexan, Babesia


The primitive type of life cycle probably had haploid individuals with asexual reproduction.[10] Bacteria and archaea exhibit a life cycle like this, and some eukaryotes apparently do too (e.g., Cryptophyta, Choanoflagellata, many Euglenozoa, many Amoebozoa, some red algae, some green algae, the imperfect fungi, some rotifers and many other groups, not necessarily haploid).[20] However, these eukaryotes probably are not primitively asexual, but have lost their sexual reproduction, or it just was not observed yet.[21][22] Many eukaryotes (including animals and plants) exhibit asexual reproduction, which may be facultative or obligate in the life cycle, with sexual reproduction occurring more or less frequently.[23]

See also


  1. ^ Graham Bell & Vassiliki Koufopanou (1991). "The architecture of the life cycle in small organisms". Philosophical Transactions: Biological Sciences. 332 (1262): 81–89. doi:10.1098/rstb.1991.0035. JSTOR 55494.
  2. ^ Dixon, P.S. 1973. Biology of the Rhodophyta. Oliver & Boyd. ISBN 0 05 002485 X
  3. ^ C. Skottsberg (1961), "Nils Eberhard Svedelius. 1873-1960", Biographical Memoirs of Fellows of the Royal Society, 7: 294–312, doi:10.1098/rsbm.1961.0023
  4. ^ Svedelius, N. 1931. Nuclear Phases and Alternation in the Rhodophyceae. In: Beihefte zum Botanischen Centralblatt. Band 48/1: 38-59.
  5. ^ L. Margulis (1996), "Archaeal-eubacterial mergers in the origin of Eukarya: phylogenetic classification of life", PNAS, 93 (3): 1071–1076, doi:10.1073/pnas.93.3.1071, PMC 40032, PMID 8577716
  6. ^ Moselio Schaechter (2009). Encyclopedia of Microbiology. Academic Press. Volume 4, p. 85.
  7. ^ a b c d e f g h i j k Díaz González, T.E., C. Fernandez-Carvajal Alvarez & J.A. Fernández Prieto. (2004). Curso de Botánica. Gijón: Trea. Online material: Botánica: Ciclos biológicos de vegetales (Vegetal life cycles, in Spanish). Departamento de Biología de Organismos y Sistemas, Universidad de Oviedo.
  8. ^ Sinden, R. E.; Hartley, R. H. "Identification of the meiotic division of malarial parasites". The Journal of Protozoology.
  9. ^ Lahr DJ, Parfrey LW, Mitchell EA, Katz LA, Lara E (July 2011). "The chastity of amoebae: re-evaluating evidence for sex in amoeboid organisms". Proc. Biol. Sci. 278 (1715): 2083–6. doi:10.1098/rspb.2011.0289. PMC 3107637. PMID 21429931.
  10. ^ a b c d e f g h i Ruppert, E. E., Fox, R. S., & Barnes, R. D. (2004). Invertebrate zoology: a functional evolutionary approach. Belmont, CA: Thomas-Brooks/Cole, p.26.
  11. ^ van den Hoek, C., D.G. Mann, and H.M. Jahns (1995). Algae: an introduction to phycology, p. 15, [1]. Cambridge University Press (623 pp).
  12. ^ O. P. Sharma. Textbook of Algae, p. 189
  13. ^ van den Hoek, C. et al. (1995), p. 207, [2].
  14. ^ van den Hoek, C. et al. (1995), pp. 124, 129.
  15. ^ Bell, G. (1989). Sex and Death in Protozoa. Cambridge University Press, p. 11, [3].
  16. ^ Salvador Soler, Noemi; Gomez Garreta, Amelia; Antonia Ribera Siguan, M. (1 August 2009). "Somatic meiosis in the life history of Bonnemaisonia asparagoides and Bonnemaisonia clavata (Bonnemaisoniales, Rhodophyta) from the Iberian peninsula". European Journal of Phycology. 44 (3): 381–393. doi:10.1080/09670260902780782 – via IngentaConnect.
  17. ^ van den Hoek, C. et al. (1995), pp. 82, 453.
  18. ^ Lewis, R.J. (1996). "Chromosomes of the brown algae". Phycologia. 35 (1): 19–40. doi:10.2216/i0031-8884-35-1-19.1.
  19. ^ Schmidt and Roberts. 1985. Foundations of Parasitology 3rd Ed. Times Mirror/Mosby College Publishing
  20. ^ Heywood, P.; Magee, P.T. (1976). "Meiosis in protists. Some structural and physiological aspects of meiosis in algae, fungi, and protozoa". Bacteriological Reviews. 40 (1): 190–240. PMC 413949. PMID 773364.
  21. ^ Shehre-Banoo Malik; Arthur W. Pightling; Lauren M. Stefaniak; Andrew M. Schurko & John M. Logsdon, Jr (2008). "An Expanded Inventory of Conserved Meiotic Genes Provides Evidence for Sex in Trichomonas vaginalis". PLoS ONE. 3 (8): e2879. doi:10.1371/journal.pone.0002879. PMC 2488364. PMID 18663385.
  22. ^ Speijer, D.; Lukeš, J.; Eliáš, M. (2015). "Sex is a ubiquitous, ancient, and inherent attribute of eukaryotic life". PNAS. 112 (29): 8827–8834. doi:10.1073/pnas.1501725112. PMC 4517231. PMID 26195746.
  23. ^ Schön, I.; Martens, K.; van Dijk, P. (2009). Lost Sex: The Evolutionary Biology of Parthenogenesis. Springer. ISBN 9789048127702.

External links

Alien (creature in Alien franchise)

The Alien (also known as Xenomorph or Internecivus raptus) is a fictional endoparasitoid extraterrestrial species that is the eponymous antagonist of the Alien film series. The species made its debut in the film Alien (1979) and reappeared in the sequels Aliens (1986), Alien 3 (1992), and Alien Resurrection (1997). It also featured in the crossover films Alien vs. Predator (2004) and Aliens vs. Predator: Requiem (2007), with cameos appearing in Predator 2 (1990), Predators (2010), and The Predator (2018). Similar creatures of slightly different designs such as the "Deacon" make a brief appearance in the Ridley Scott film Prometheus (2012) along with the "Neomorph" and a variation of the Xenomorph which appear in the sequel Alien: Covenant (2017). In addition, the Alien appears in various literature and video game spin-offs from the franchises.

The Alien design is credited to Swiss surrealist and artist H. R. Giger, originating in a lithograph titled Necronom IV and refined for the series's first film, Alien. The practical effects for the Alien's head were designed and constructed by Italian special effects designer Carlo Rambaldi. The species's design and life cycle have been extensively augmented, sometimes inconsistently, throughout each film.

Unlike many other extraterrestrial races in science fiction (such as the Daleks and Cybermen in Doctor Who, and the Klingons and Borg in Star Trek), the Aliens are not sapient tool-makers: They lack a technological civilization of any kind, and are primal predatory creatures with no higher goals than the propagation and self-preservation of their species, including the elimination of other lifeforms that may pose a threat to their existence. Like wasps or termites, Aliens are eusocial, with a single fertile queen breeding a caste of warriors, workers, or other specialists strains. The Aliens' biological life cycle involves traumatic implantation of endoparasitoid larvae inside living hosts; these "chestburster" larvae erupt from the host's body after a short incubation period, rapidly mature from juvenile into adulthood within hours, and seek out more hosts for implantation.

Alternation of generations

Alternation of generations (also known as metagenesis) is the type of life cycle that occurs in those plants and algae in the Archaeplastida and the Heterokontophyta that have distinct sexual haploid and asexual diploid stages. In these groups, a multicellular gametophyte, which is haploid with n chromosomes, alternates with a multicellular sporophyte, which is diploid with 2n chromosomes, made up of n pairs. A mature sporophyte produces spores by meiosis, a process which reduces the number of chromosomes to half, from 2n to n.

The haploid spores germinate and grow into a haploid gametophyte. At maturity, the gametophyte produces gametes by mitosis, which does not alter the number of chromosomes. Two gametes (originating from different organisms of the same species or from the same organism) fuse to produce a zygote, which develops into a diploid sporophyte. This cycle, from gametophyte to gametophyte (or equally from sporophyte to sporophyte), is the way in which all land plants and many algae undergo sexual reproduction.

The relationship between the sporophyte and gametophyte varies among different groups of plants. In those algae which have alternation of generations, the sporophyte and gametophyte are separate independent organisms, which may or may not have a similar appearance. In liverworts, mosses and hornworts, the sporophyte is less well developed than the gametophyte and is largely dependent on it. Although moss and hornwort sporophytes can photosynthesise, they require additional photosynthate from the gametophyte to sustain growth and spore development and depend on it for supply of water, mineral nutrients and nitrogen. By contrast, in all modern vascular plants the gametophyte is less well developed than the sporophyte, although their Devonian ancestors had gametophytes and sporophytes of approximately equivalent complexity. In ferns the gametophyte is a small flattened autotrophic prothallus on which the young sporophyte is briefly dependent for its nutrition. In flowering plants, the reduction of the gametophyte is much more extreme; it consists of just a few cells which grow entirely inside the sporophyte.

Animals develop differently. They directly produce haploid gametes. No haploid spores capable of dividing are produced, so they do not have a haploid gametophyte alternating with a diploid sporophyte. (Some insects have a sex-determining system whereby haploid males are produced from unfertilized eggs; however the females are diploid.)

Life cycles of plants and algae with alternating haploid and diploid multicellular stages are referred to as diplohaplontic (the equivalent terms haplodiplontic, diplobiontic or dibiontic are also in use). Life cycles, such as those of animals, in which there is only a diploid multicellular stage are referred to as diplontic. Life cycles in which there is only a haploid multicellular stage are referred to as haplontic.

Aquaculture of brine shrimp

Brine shrimp have the ability to produce dormant eggs, known as cysts. This has led to the extensive use of brine shrimp in aquaculture. The cysts may be stored for long periods and hatched on demand to provide a convenient form of live feed for larval fish and crustaceans.From cysts, brine shrimp nauplii can readily be used to feed to fish and crustacean larvae just after one-day incubation. Instar I (the nauplii that just hatched and with large yolk reserves in their body) and instar II nauplii (the nauplii after first moult and with functional digestive tracts) are more widely used in aquaculture, for the reasons they are easy for operation, nutrients rich, and of small size which makes them suitable for feeding fish and crustacean larvae live or after drying.

Asexual reproduction

Asexual reproduction is a type of reproduction by which offspring arise from a single organism, and inherit the genes of that parent only; it does not involve the fusion of gametes, and almost never changes the number of chromosomes. Asexual reproduction is the primary form of reproduction for single-celled organisms such as archaea and bacteria. Many plants and fungi sometimes reproduce asexually. Some asexual cells die when they are very young.

While all prokaryotes reproduce without the formation and fusion of gametes, mechanisms for lateral gene transfer such as conjugation, transformation and transduction can be likened to sexual reproduction in the sense of genetic recombination in meiosis. A complete lack of sexual reproduction is relatively rare among multi-cellular organisms, particularly animals. It is not entirely understood why the ability to reproduce sexually is so common among them. Current hypotheses suggest that asexual reproduction may have short term benefits when rapid population growth is important or in stable environments, while sexual reproduction offers a net advantage by allowing more rapid generation of genetic diversity, allowing adaptation to changing environments. Developmental constraints may underlie why few animals have relinquished sexual reproduction completely in their life-cycles. Another constraint on switching from sexual to asexual reproduction would be the concomitant loss of meiosis and the protective recombinational repair of DNA damage afforded as one function of meiosis.

Circle of Life (disambiguation)

"Circle of Life" is a Disney song from the 1994 animated film The Lion King.

Circle of Life or circle of life may also refer to:

Circle of life, biological life cycle of procreation, birth, life, death and predation

Circle of life, social circle, a community or subculture of a location

Circle of life, called Ensō in Zen

Corynosoma australe

Corynosoma autrale is a species of acanthocephalan (also known as thorny-headed worms, or spiny headed worms). This species usually infects pinnipeds; the semi-aquatic fin-footed marine mammals most commonly known as seals and sea lions. Pinniped infections are not exclusive, recently C. australe has been discovered in Magellanic penguins. (Spheniscus magellanicus)


Fecundity, in human demography and population biology, is the potential for reproduction of an organism or population, measured by the number of gametes (eggs), seed set, or asexual propagules. Fecundity is similar to fertility, the natural capability to produce offspring. A lack of fertility is infertility while a lack of fecundity would be called sterility.

Human demography considers only human fecundity which is often intentionally limited through contraception, while population biology studies all organisms. The term fecundity in population biology is often used to describe the rate of offspring production after one time step (often annual). In this sense, fecundity may include both birth rates and survival of young to that time step. Fecundity is under both genetic and environmental control, and is the major measure of fitness. Fecundation is another term for fertilization. Superfecundity or retrofecundity refers to an organism's ability to store another organism's sperm (after copulation) and fertilize its own eggs from that store after a period of time, essentially making it appear as though fertilization occurred without sperm (i.e. parthenogenesis).Fecundity is important and well studied in the field of population ecology. Fecundity can increase or decrease in a population according to current conditions and certain regulating factors. For instance, in times of hardship for a population, such as a lack of food or high temperatures, juvenile and eventually adult fecundity has been shown to decrease (i.e. due to a lack of resources the juvenile individuals are unable to reproduce, eventually the adults will run out of resources and reproduction will cease).

Fecundity has also been shown to increase in ungulates with relation to warmer weather.In sexual evolutionary biology, especially in sexual selection, fecundity is contrasted to reproductivity.

In obstetrics and gynecology, fecundability is the probability of being pregnant in a single menstrual cycle, and fecundity is the probability of achieving a live birth within a single cycle.

From Dust

From Dust is a god video game, designed by Éric Chahi and developed by Ubisoft Montpellier. The game was released for Microsoft Windows, PlayStation Network, and Xbox Live Arcade in 2011. Described as a spiritual successor to Populous, the game revolves around The Breath, which was summoned by a tribe to help them seek and recover their lost knowledge. In the game, players, controlling a cursor, can manipulate matter such as lava, soil, and water. Players can help the tribespeople to overcome challenges including finding different totems and overcoming natural disasters. In addition to the story mode, the game features a Challenge mode which offers a shorter, but harder experience.

Originally starting its life as a strategy game, From Dust marked the return of Éric Chahi to the video game industry following an extended sabbatical after the completion of his last game, Heart of Darkness. The project was created as a result of his fascination with volcanos, and his desire to combine the ambivalence and violent characteristics of their nature in a new video game. The team was further inspired by African and New Guinean tribes, Conway's Game of Life, works of Polish painter Zdzisław Beksiński, and Koyaanisqatsi. Some features, such as the biological life cycle of the tribespeople, were left out of the game because of the huge amount of work they would require. Ubisoft was originally doubtful about the project but was later convinced by Chahi. The game was made by a small team within the Montpellier studio, so was considered an independent game produced by a large publisher. The game was announced at E3 2010 as Project Dust.

The game received a generally positive reception on release, with critics praising the game's physics, simulation, openness and graphics, while criticizing the game's artificial intelligence and camera angles. Opinions on the game's Challenge mode and mission design were polarizing. The PC version of the game fared worse than other platforms for its technical issues and digital rights management. The game was a commercial success for Ubisoft, selling over half a million copies and became Ubisoft's fastest-selling digital game. Despite its success, Chahi confirmed that he will not return to develop a sequel.


AvGametogenesis is a biological process by which diploid or haploid precursor cells undergo cell division and differentiation to form mature haploid gametes. Depending on the biological life cycle of the organism, gametogenesis occurs by meiotic division of diploid gametocytes into various gametes, or by mitosis. For example, plants produce gametes through mitosis in gametophytes. The gametophytes grow from haploid spores after sporic meiosis. The existence of a multicellular, haploid phase in the life cycle between meiosis and gametogenesis is also referred to as alternation of generations.

Human reproduction

Human reproduction is any form of sexual reproduction resulting in human fertilization. It typically involves sexual intercourse between a man and a woman. During sexual intercourse, the interaction between the male and female reproductive systems results in fertilization of the woman's ovum by the man's sperm. These are specialized reproductive cells called gametes, created in a process called meiosis. While normal cells contains 46 chromosomes, 23 pairs, gamete cells only contain 23 chromosomes, and it is when these two cells merge into one zygote cell that genetic recombination occurs and the new zygote contains 23 chromosomes from each parent, giving them 23 pairs. A typical 9-month gestation period is followed by childbirth. The fertilization of the ovum may be achieved by artificial insemination methods, which do not involve sexual intercourse.

Ichthyology and GIS

A Geographic Information System is a tool for mapping and analyzing data. The ability to layer many features onto the same map and select or unselect as needed allows for a multitude of views and ease of interpreting data. More important, this allows for in depth scientific analysis and problem solving.

Ichthyology involves many areas of study related to fishes and their habitat. The natural habitat is water, but fish are dependent upon many other factors. Water quality, type, food, cover, sediment are essential for the life cycle of any given fish. Being able to map the presence of certain species with layers of these features provides invaluable insight into species requirements. GIS is an essential tool that allows immediate visualization of all data present and to accurately interpret impacts of habitat degradation or species success.

Life history theory

Life history theory is an analytical framework designed to study the diversity of life history strategies used by different organisms throughout the world, as well as the causes and results of the variation in their life cycles. It is a theory of biological evolution that seeks to explain aspects of organisms' anatomy and behavior by reference to the way that their life histories—including their reproductive development and behaviors, life span and post-reproductive behavior—have been shaped by natural selection. A life history strategy is the "age- and stage-specific patterns" and timing of events that make up an organism's life, such as birth, weaning, maturation, death, etc. These events, notably juvenile development, age of sexual maturity, first reproduction, number of offspring and level of parental investment, senescence and death, depend on the physical and ecological environment of the organism.

The theory was developed in the 1950s and is used to answer questions about topics such as organism size, age of maturation, number of offspring, life span, and many others. In order to study these topics, life history strategies must be identified, and then models are constructed to study their effects. Finally, predictions about the importance and role of the strategies are made, and scientists use these predictions to understand how evolution affects the ordering and length of life history events in an organism's life, particularly the lifespan and period of reproduction. Life history theory draws on an evolutionary foundation, and studies the effects of natural selection on organisms, both throughout their lifetime and across generations. It also uses measures of evolutionary fitness to determine if organisms are able to maximize or optimize this fitness, by allocating resources to a range of different demands throughout the organism's life. It serves as a method to investigate further the "many layers of complexity of organisms and their worlds".Organisms have evolved a great variety of life histories, from Pacific salmon, which produce thousands of eggs at one time and then die, to human beings, who produce a few offspring over the course of decades. The theory depends on principles of evolutionary biology and ecology and is widely used in other areas of science.


Meiosis ( (listen); from Greek μείωσις, meiosis, which means lessening) is a special type of cell division that reduces the chromosome number by half, creating four haploid cells, each genetically distinct from the parent cell that gave rise to them. This process occurs in all sexually reproducing single-celled and multicellular eukaryotes, including animals, plants, and fungi. Errors in meiosis resulting in aneuploidy are the leading known cause of miscarriage and the most frequent genetic cause of developmental disabilities.In meiosis, DNA replication is followed by two rounds of cell division to produce four daughter cells, each with half the number of chromosomes as the original parent cell. The two meiotic divisions are known as Meiosis I and Meiosis II. Before meiosis begins, during S phase of the cell cycle, the DNA of each chromosome is replicated so that it consists of two identical sister chromatids, which remain held together through sister chromatid cohesion. This S-phase can be referred to as "premeiotic S-phase" or "meiotic S-phase". Immediately following DNA replication, meiotic cells enter a prolonged G2-like stage known as meiotic prophase. During this time, homologous chromosomes pair with each other and undergo genetic recombination, a programmed process in which DNA is cut and then repaired, which allows them to exchange some of their genetic information. A subset of recombination events results in crossovers, which create physical links known as chiasmata (singular: chiasma, for the Greek letter Chi (X)) between the homologous chromosomes. In most organisms, these links are essential to direct each pair of homologous chromosomes to segregate away from each other during Meiosis I, resulting in two haploid cells that have half the number of chromosomes as the parent cell. During Meiosis II, the cohesion between sister chromatids is released and they segregate from one another, as during mitosis. In some cases all four of the meiotic products form gametes such as sperm, spores, or pollen. In female animals, three of the four meiotic products are typically eliminated by extrusion into polar bodies, and only one cell develops to

produce an ovum. Because the number of chromosomes is halved during meiosis, gametes can fuse (i.e. fertilization) to form a diploid

zygote that contains two copies of each chromosome, one from each parent. Thus, alternating cycles of meiosis and fertilization enable sexual reproduction, with successive generations maintaining the same number of chromosomes. For example, diploid human

cells contain 23 pairs of chromosomes including 1 pair of sex chromosomes (46 total), half of maternal origin and half of paternal origin. Meiosis produces haploid gametes (ova or sperm) that contain one set of 23 chromosomes. When two gametes (an egg and a sperm) fuse, the resulting zygote is once again diploid, with the mother and father each contributing 23 chromosomes. This same pattern, but not the same number of chromosomes, occurs in all organisms that utilize meiosis.


Methoprene is a juvenile hormone (JH) analog which acts as a growth regulator when used as an insecticide. It is an amber-colored liquid with a faint fruity odor. According to the MSDS, methoprene is a material that may be irritating to the mucous membranes and upper respiratory tract, may be harmful by inhalation, ingestion, or skin absorption, may cause eye, skin, or respiratory system irritation and is very toxic to aquatic life. The GHS signal word is "Warning," with notes such as P273 Avoid release into the environment and P391 collect spillage. It is used in drinking water cisterns to control mosquitoes which spread dengue fever and malaria.Methoprene does not kill insects. Instead, it interferes with an insect’s life cycle and prevents it from reaching maturity or

reproducing. Juvenile growth hormones must be absent for a pupa to molt to an adult, so methoprene-treated larvae will be unable to successfully change from pupae to adults. This breaks the biological life cycle of the insect, preventing recurring infestation. Methoprene is used in the production of a number of foods, including meat, milk, mushrooms, peanuts, rice, and cereals. It also has several uses on domestic animals (pets) for controlling fleas. Methoprene is considered a biological pesticide because rather than controlling target pests through direct toxicity, methoprene interferes with an insect’s lifecycle and prevents it from reaching maturity or reproducing.Methoprene is commonly used as a mosquito larvicide used to help stop the spread of the West Nile virus.

Methoprene is also used as a food additive in cattle feed to prevent fly breeding in the manure.

Methoprene is suspected to be highly toxic to lobsters.

Organizational life cycle

The organizational life cycle is the life cycle of an organization from its creation to its termination. It also refers to the expected sequence of advancements experienced by an organization, as opposed to a randomized occurrence of events. The relevance of a biological life cycle relating to the growth of an organization, was discovered by organizational researchers many years ago. This was apparent as organizations had a distinct conception, periods of expansion and eventually, termination.

Santa Barbara Museum of Natural History Sea Center

The Santa Barbara Museum of Natural History Sea Center, briefly known as the Ty Warner Sea Center, is a museum owned and operated by the Santa Barbara Museum of Natural History and is located on Santa Barbara's Stearns Wharf. The Sea Center focuses on the marine life and the related conservation of the Santa Barbara Channel.

Thismia rodwayi

Thismia rodwayi, or fairy lantern, is a non-chlorophyllous plant belonging to the Burmanniaceae family, found in the southern states of Australia (Tasmania, Victoria and New South Wales) and in several locations in New Zealand.

The small number of known individuals of this species has put it under Schedule 5 (Rare) of the Tasmanian Threatened Species Protection Act 1995. However, Thismia rodwayi is not considered threatened by the International Union for Conservation of Nature (IUCN).


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