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167-445: Plant breeding can be performed using many different techniques, ranging from the selection of the most desirable plants for propagation, to methods that make use of knowledge of genetics and chromosomes, to more complex molecular techniques. Genes in a plant are what determine what type of qualitative or quantitative traits it will have. Plant breeders strive to create a specific outcome of plants and potentially new plant varieties, and in

334-461: A Holliday junction . Following this, more DNA synthesis occurs on the invading strand (i.e., one of the original 3' overhangs), effectively restoring the strand on the homologous chromosome that was displaced during strand invasion. After the stages of resection, strand invasion and DNA synthesis, the DSBR and SDSA pathways become distinct. The DSBR pathway is unique in that the second 3' overhang (which

501-457: A nuclease domain, which cuts the single strand of DNA that emerges from the unzipping process. This unzipping continues until RecBCD encounters a specific nucleotide sequence (5'-GCTGGTGG-3') known as a Chi site . Upon encountering a Chi site, the activity of the RecBCD enzyme changes drastically. DNA unwinding pauses for a few seconds and then resumes at roughly half the initial speed. This

668-505: A D-loop. If the D-loop is cut, another swapping of strands forms a cross-shaped structure called a Holliday junction . Resolution of the Holliday junction by some combination of RuvABC or RecG can produce two recombinant DNA molecules with reciprocal genetic types, if the two interacting DNA molecules differ genetically. Alternatively, the invading 3’ end near Chi can prime DNA synthesis and form

835-511: A DNA damage. In one of the earliest steps, the stress-activated protein kinase, c-Jun N-terminal kinase (JNK) , phosphorylates SIRT6 on serine 10 in response to double-strand breaks or other DNA damage. This post-translational modification facilitates the mobilization of SIRT6 to DNA damage sites, and is required for efficient recruitment of poly (ADP-ribose) polymerase 1 (PARP1) to DNA break sites and for efficient repair of DSBs. PARP1 protein starts to appear at DNA damage sites in less than

1002-407: A barrier to all DNA-based processes that require recruitment of enzymes to their sites of action. To allow homologous recombination (HR) DNA repair, the chromatin must be remodeled. In eukaryotes, ATP dependent chromatin remodeling complexes and histone-modifying enzymes are two predominant factors employed to accomplish this remodeling process. Chromatin relaxation occurs rapidly at the site of

1169-567: A better cost/benefit ratio than non-participatory approaches, and suggested incorporating participatory plant breeding with evolutionary plant breeding. Evolutionary plant breeding describes practices which use mass populations with diverse genotypes grown under competitive natural selection. Survival in common crop cultivation environments is the predominant method of selection, rather than direct selection by growers and breeders. Individual plants that are favored under prevailing growing conditions, such as environment and inputs, contribute more seed to

1336-533: A collapsed replication fork and is fixed by several pathways of homologous recombination including the RecBCD pathway. In this pathway, a three-subunit enzyme complex called RecBCD initiates recombination by binding to a blunt or nearly blunt end of a break in double-strand DNA. After RecBCD binds the DNA end, the RecB and RecD subunits begin unzipping the DNA duplex through helicase activity. The RecB subunit also has

1503-420: A compaction state close to its pre-damage level after about 20 min. In vertebrates the locations at which recombination occurs are determined by the binding locations of PRDM9 , a protein which recognizes a specific sequence motif by its zinc finger array. At these sites, another protein, SPO11 catalyses recombination-initiating double strand breaks (DSBs), a subset of which are repaired by recombination with

1670-407: A cross of related species or genera that do not normally sexually reproduce with each other. These crosses are referred to as Wide crosses . For example, the cereal triticale is a wheat and rye hybrid. The cells in the plants derived from the first generation created from the cross contained an uneven number of chromosomes and as a result was sterile. The cell division inhibitor colchicine

1837-460: A few varieties that became dominant in some locations almost disappeared in others; poorly-adapted varieties disappeared everywhere. Evolutionary breeding populations have been used to establish self-regulating plant–pathogen systems. Examples include barley, where breeders were able to improve resistance to Rynchosporium secalis scald over 45 generations. An evolutionary breeding project grew F5 hybrid bulk soybean populations on soil infested by

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2004-487: A gene necessary for the strand exchange reaction, a key step in homologous recombinational repair, there is functional homology from viruses to humans (i. e. uvsX in phage T4; recA in E. coli and other bacteria, and rad51 and dmc1 in yeast and other eukaryotes, including humans). Multiplicity reactivation has also been demonstrated in numerous pathogenic viruses. Coronaviruses are capable of genetic recombination when at least two viral genomes are present in

2171-456: A goal to create a typology or taxonomy of polities , as typologies of political systems are not obvious. It is especially important in the political science fields of comparative politics and international relations . Like all categories discerned within forms of government, the boundaries of government classifications are either fluid or ill-defined. Superficially, all governments have an official de jure or ideal form. The United States

2338-425: A governing body, such as a legislature or jury . Some governments combine both direct and indirect democratic governance, wherein the citizenry selects representatives to administer day-to-day governance, while also reserving the right to govern directly through popular initiatives , referendums (plebiscites), and the right of recall . In a constitutional democracy the powers of the majority are exercised within

2505-468: A growing European mutiny over genetically modified crops by banning the planting of a widely grown pest-resistant corn variety. " The debate encompasses the ecological impact of genetically modified plants , the safety of genetically modified food and concepts used for safety evaluation like substantial equivalence . Such concerns are not new to plant breeding. Most countries have regulatory processes in place to help ensure that new crop varieties entering

2672-438: A homologous chromosome. The search process induces stretching of the DNA duplex, which enhances homology recognition (a mechanism termed conformational proofreading ). Upon finding such a sequence, the single-stranded nucleoprotein filament moves into the homologous recipient DNA duplex in a process called strand invasion . The invading 3' overhang causes one of the strands of the recipient DNA duplex to be displaced, to form

2839-539: A model for recombination in meiosis which introduced key details of how the process can work, including the exchange of material between chromosomes through Holliday junctions . In 1983, Jack Szostak and colleagues presented a model now known as the DSBR pathway , which accounted for observations not explained by the Holliday model. During the next decade, experiments in Drosophila , budding yeast and mammalian cells led to

3006-463: A narrower scope, such as the government of Portugal , which is actually more similar to the concept of "administration" . The moment and place that the phenomenon of human government developed is lost in time; however, history does record the formations of early governments. About 5,000 years ago, the first small city-states appeared. By the third to second millenniums BC, some of these had developed into larger governed areas: Sumer , ancient Egypt ,

3173-444: A plant with the desired trait or traits faster than classical breeding because the majority of the plant's genome is not altered. To genetically modify a plant, a genetic construct must be designed so that the gene to be added or removed will be expressed by the plant. To do this, a promoter to drive transcription and a termination sequence to stop transcription of the new gene, and the gene or genes of interest must be introduced to

3340-459: A protein called Spo11 makes a targeted double-strand break in DNA. These sites are non-randomly located on the chromosomes; usually in intergenic promoter regions and preferentially in GC-rich domains These double-strand break sites often occur at recombination hotspots , regions in chromosomes that are about 1,000–2,000 base pairs in length and have high rates of recombination. The absence of

3507-430: A quarter of the world's population under democratically backsliding governments. Homologous recombination Homologous recombination is a type of genetic recombination in which genetic information is exchanged between two similar or identical molecules of double-stranded or single-stranded nucleic acids (usually DNA as in cellular organisms but may be also RNA in viruses ). Homologous recombination

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3674-413: A recombination event may have been a critical step in the evolution of SARS-CoV-2's capability to infect humans. Recombination events are likely key steps in the evolutionary process that leads to the emergence of new human coronaviruses. During COVID-19 pandemic in 2020, many genomic sequences of Australian SARS‐CoV‐2 isolates have deletions or mutations (29742G>A or 29742G>U; "G19A" or "G19U")in

3841-464: A recombination hotspot between two genes on the same chromosome often means that those genes will be inherited by future generations in equal proportion. This represents linkage between the two genes greater than would be expected from genes that independently assort during meiosis. Double-strand breaks can be repaired through homologous recombination, polymerase theta-mediated end joining (TMEJ) or through non-homologous end joining (NHEJ). NHEJ

4008-401: A regional level. Efforts to strengthen breeders' rights, for example, by lengthening periods of variety protection, are ongoing. Government A government is the system or group of people governing an organized community, generally a state . In the case of its broad associative definition, government normally consists of legislature , executive , and judiciary . Government

4175-501: A replication fork. This type of resolution produces only one type of recombinant (non-reciprocal). Bacteria appear to use the RecF pathway of homologous recombination to repair single-strand gaps in DNA. When the RecBCD pathway is inactivated by mutations and additional mutations inactivate the SbcCD and ExoI nucleases, the RecF pathway can also repair DNA double-strand breaks. In the RecF pathway

4342-476: A ring-shaped ATPase , are loaded onto opposite sides of the Holliday junction, where they act as twin pumps that provide the force for branch migration. Between those two rings of RuvB, two sets of the RuvA protein assemble in the center of the Holliday junction such that the DNA at the junction is sandwiched between each set of RuvA. The strands of both DNA duplexes—the "donor" and the "recipient" duplexes—are unwound on

4509-431: A second, with half maximum accumulation within 1.6 seconds after the damage occurs. Next the chromatin remodeler Alc1 quickly attaches to the product of PARP1 action, a poly-ADP ribose chain, and Alc1 completes arrival at the DNA damage within 10 seconds of the occurrence of the damage. About half of the maximum chromatin relaxation, presumably due to action of Alc1, occurs by 10 seconds. This then allows recruitment of

4676-842: A single person infected with a virus variant identical to the Wuhan WIV04 isolates, or simultaneously with another primary case infected with a virus containing the 11083G > T mutation. Linkage disequilibrium analysis confirmed that RNA recombination with the 11083G > T mutation also contributed to the increase of mutations among the viral progeny. The findings indicate that the 11083G > T mutation of SARS-CoV-2 spread during shipboard quarantine and arose through de novo RNA recombination under positive selection pressure. In addition, in three patients in this cruise, two mutations 29736G > T and 29751G > T ("G13" and "G28") were also located in Coronavirus 3′ stem-loop II-like motif (s2m) , as "G28"

4843-407: A standalone entity or as a hybrid system of the main three. Scholars generally refer to a dictatorship as either a form of authoritarianism or totalitarianism. An autocracy is a system of government in which supreme power is concentrated in the hands of one person, whose decisions are subject to neither external legal restraints nor regularized mechanisms of popular control (except perhaps for

5010-477: A striking parallel with star formation, new structures suddenly appeared, together with a new level of complexity. Like stars, cities and states reorganize and energize the smaller objects within their gravitational field. Another explanation includes the need to properly manage infrastructure projects such as water infrastructure. Historically, this required centralized administration and complex social organisation, as seen in regions like Mesopotamia. However, there

5177-406: A technique called chromosome engineering may also be used. When a desirable trait has been bred into a species, a number of crosses to the favored parent are made to make the new plant as similar to the favored parent as possible. Returning to the example of the mildew resistant pea being crossed with a high- yielding but susceptible pea, to make the mildew resistant progeny of the cross most like

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5344-502: A type of horizontal gene transfer in which DNA is transferred from one bacterium to another by a virus . Foreign, bacterial DNA is sometimes misincorporated in the capsid head of bacteriophage virus particles as DNA is packaged into new bacteriophages during viral replication. When these new bacteriophages infect other bacteria, DNA from the previous host bacterium is injected into the new bacterial host as double-strand DNA. The RecBCD enzyme then incorporates this double-strand DNA into

5511-428: A variety of hybrid regimes . Modern classification systems also include monarchies as a standalone entity or as a hybrid system of the main three. Historically prevalent forms of government include monarchy, aristocracy , timocracy , oligarchy , democracy , theocracy , and tyranny . These forms are not always mutually exclusive, and mixed governments are common. The main aspect of any philosophy of government

5678-566: A whole plant. Such a method is referred to as embryo rescue . This technique has been used to produce new rice for Africa , an interspecific cross of Asian rice Oryza sativa and African rice O. glaberrima . Hybrids may also be produced by a technique called protoplast fusion. In this case protoplasts are fused, usually in an electric field. Viable recombinants can be regenerated in culture. Chemical mutagens like ethyl methanesulfonate (EMS) and dimethyl sulfate (DMS), radiation , and transposons are used for mutagenesis . Mutagenesis

5845-516: Is widely used by cells to accurately repair harmful DNA breaks that occur on both strands of DNA, known as double-strand breaks (DSB), in a process called homologous recombinational repair (HRR). Homologous recombination also produces new combinations of DNA sequences during meiosis , the process by which eukaryotes make gamete cells, like sperm and egg cells in animals. These new combinations of DNA represent genetic variation in offspring, which in turn enables populations to adapt during

6012-429: Is a DNA repair mechanism which, unlike homologous recombination, does not require a long homologous sequence to guide repair. Whether homologous recombination or NHEJ is used to repair double-strand breaks is largely determined by the phase of cell cycle . Homologous recombination repairs DNA before the cell enters mitosis (M phase). It occurs during and shortly after DNA replication , in the S and G 2 phases of

6179-485: Is a federal constitutional republic, while the former Soviet Union was a federal socialist republic . However self-identification is not objective, and as Kopstein and Lichbach argue, defining regimes can be tricky, especially de facto , when both its government and its economy deviate in practice. For example, Voltaire argued that "the Holy Roman Empire is neither Holy, nor Roman, nor an Empire". In practice,

6346-429: Is a form of government that places power in the hands of a small, elite ruling class , such as a hereditary nobility or privileged caste . This class exercises minority rule , often as a landed timocracy , wealthy plutocracy , or oligarchy . Many monarchies were aristocracies, although in modern constitutional monarchies, the monarch may have little effective power. The term aristocracy could also refer to

6513-427: Is a major DNA repair process in bacteria. It is also important for producing genetic diversity in bacterial populations, although the process differs substantially from meiotic recombination, which repairs DNA damages and brings about diversity in eukaryotic genomes . Homologous recombination has been most studied and is best understood for Escherichia coli . Double-strand DNA breaks in bacteria are repaired by

6680-597: Is a means by which organizational policies are enforced, as well as a mechanism for determining policy. In many countries, the government has a kind of constitution , a statement of its governing principles and philosophy. While all types of organizations have governance , the term government is often used more specifically to refer to the approximately 200 independent national governments and subsidiary organizations . The main types of modern political systems recognized are democracies , totalitarian regimes , and, sitting between these two, authoritarian regimes with

6847-491: Is a nearly universal biological mechanism. The discovery of genes for homologous recombination in protists —a diverse group of eukaryotic microorganisms —has been interpreted as evidence that homologous recombination emerged early in the evolution of eukaryotes. Since their dysfunction has been strongly associated with increased susceptibility to several types of cancer , the proteins that facilitate homologous recombination are topics of active research. Homologous recombination

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7014-448: Is a political concept in which a group of members are bound together by covenant with a governing representative head . The term "federalism" is also used to describe a system of government in which sovereignty is constitutionally divided between a central governing authority and constituent political units, variously called states, provinces or otherwise. Federalism is a system based upon democratic principles and institutions in which

7181-503: Is about two million base pairs at the site of a DNA double-strand break. γH2AX does not, itself, cause chromatin decondensation, but within 30 seconds of irradiation, RNF8 protein can be detected in association with γH2AX. RNF8 mediates extensive chromatin decondensation, through its subsequent interaction with CHD4 , a component of the nucleosome remodeling and deacetylase complex NuRD . After undergoing relaxation subsequent to DNA damage, followed by DNA repair, chromatin recovers to

7348-425: Is achieved by adding a specific gene or genes to a plant, or by knocking down a gene with RNAi , to produce a desirable phenotype . The plants resulting from adding a gene are often referred to as transgenic plants . If for genetic modification genes of the species or of a crossable plant are used under control of their native promoter, then they are called cisgenic plants . Sometimes genetic modification can produce

7515-414: Is also evidence for recombination in some RNA viruses , specifically positive-sense ssRNA viruses like retroviruses , picornaviruses , and coronaviruses . There is controversy over whether homologous recombination occurs in negative-sense ssRNA viruses like influenza . In RNA viruses, homologous recombination can be either precise or imprecise. In the precise type of RNA-RNA recombination, there

7682-453: Is also known as molecular breeding . Sometimes many different genes can influence a desirable trait in plant breeding. The use of tools such as molecular markers or DNA fingerprinting can map thousands of genes. This allows plant breeders to screen large populations of plants for those that possess the trait of interest. The screening is based on the presence or absence of a certain gene as determined by laboratory procedures, rather than on

7849-453: Is also used in gene targeting , a technique for introducing genetic changes into target organisms. For their development of this technique, Mario Capecchi , Martin Evans and Oliver Smithies were awarded the 2007 Nobel Prize for Physiology or Medicine ; Capecchi and Smithies independently discovered applications to mouse embryonic stem cells, however the highly conserved mechanisms underlying

8016-582: Is an important and controversial issue. Production of new varieties is dominated by commercial plant breeders, who seek to protect their work and collect royalties through national and international agreements based in intellectual property rights . The range of related issues is complex. In the simplest terms, critics of the increasingly restrictive regulations argue that, through a combination of technical and economic pressures, commercial breeders are reducing biodiversity and significantly constraining individuals (such as farmers) from developing and trading seed on

8183-583: Is archaeological evidence that shows similar successes with more egalitarian and decentralized complex societies. Starting at the end of the 17th century, the prevalence of republican forms of government grew. The English Civil War and Glorious Revolution in England, the American Revolution , and the French Revolution contributed to the growth of representative forms of government. The Soviet Union

8350-422: Is broader, covering molecular biology , cytology , systematics , physiology , pathology , entomology , chemistry , and statistics ( biometrics ). It has also developed its own technology. One major technique of plant breeding is selection , the process of selectively propagating plants with desirable characteristics and eliminating or "culling" those with less desirable characteristics. Another technique

8517-471: Is called an aristocracy. In other kinds of Commonwealth there can be none: for either one, or more, or all, must have the sovereign power (which I have shown to be indivisible) entire. According to Yale professor Juan José Linz , there a three main types of political systems today: democracies , totalitarian regimes and, sitting between these two, authoritarian regimes with hybrid regimes . Another modern classification system includes monarchies as

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8684-440: Is clearly a bacterial adaptation for DNA transfer. In order for a bacterium to bind, take up and integrate donor DNA into its resident chromosome by homologous recombination, it must first enter a special physiological state termed competence . The RecA / Rad51 / DMC1 gene family plays a central role in homologous recombination during bacterial transformation as it does during eukaryotic meiosis and mitosis. For instance,

8851-450: Is controlled by the sequence context of the two recombining strands of RNA: sequences rich in adenine and uracil decrease crossover precision. Homologous recombination is important in facilitating viral evolution . For example, if the genomes of two viruses with different disadvantageous mutations undergo recombination, then they may be able to regenerate a fully functional genome. Alternatively, if two similar viruses have infected

9018-485: Is critical for cell immortalization , a key feature of cancer. Most cancers maintain telomeres by upregulating telomerase. However, in several types of human cancer, a BIR-like pathway helps to sustain some tumors by acting as an alternative mechanism of telomere maintenance. This fact has led scientists to investigate whether such recombination-based mechanisms of telomere maintenance could thwart anti-cancer drugs like telomerase inhibitors . Homologous recombination

9185-522: Is cut on the crossing strand and the other Holliday junction is cut on the non-crossing strand (in Figure 5, along the horizontal purple arrowheads at one Holliday junction and along the vertical orange arrowheads at the other). Alternatively, if the two Holliday junctions are cut on the crossing strands (along the horizontal purple arrowheads at both Holliday junctions in Figure 5), then chromosomes without crossover will be produced. Homologous recombination via

9352-416: Is found frequently in DNA, about once every 64 nucleotides. Before cutting, RuvC likely gains access to the Holliday junction by displacing one of the two RuvA tetramers covering the DNA there. Recombination results in either "splice" or "patch" products, depending on how RuvC cleaves the Holliday junction. Splice products are crossover products, in which there is a rearrangement of genetic material around

9519-426: Is how political power is obtained, with the two main forms being electoral contest and hereditary succession . A government is the system to govern a state or community. The Columbia Encyclopedia defines government as "a system of social control under which the right to make laws, and the right to enforce them, is vested in a particular group in society". While all types of organizations have governance ,

9686-679: Is important for ensuring food security by developing new varieties that are higher yielding, disease resistant, drought tolerant or regionally adapted to different environments and growing conditions. A recent study shows that without plant breeding, Europe would have produced 20% fewer arable crops over the last 20 years, consuming an additional 21.6 million hectares (53 million acres) of land and emitting 4 billion tonnes (3.9 × 10 long tons; 4.4 × 10 short tons) of carbon. Wheat species created for Morocco are currently being crossed with plants to create new varieties for northern France. Soy beans, which were previously grown predominantly in

9853-493: Is likely because the slower RecB helicase unwinds the DNA after Chi, rather than the faster RecD helicase, which unwinds the DNA before Chi. Recognition of the Chi site also changes the RecBCD enzyme so that it cuts the DNA strand with Chi and begins loading multiple RecA proteins onto the single-stranded DNA with the newly generated 3' end. The resulting RecA-coated nucleoprotein filament then searches out similar sequences of DNA on

10020-731: Is more frequent than in yeast. In the early 1900s, William Bateson and Reginald Punnett found an exception to one of the principles of inheritance originally described by Gregor Mendel in the 1860s. In contrast to Mendel's notion that traits are independently assorted when passed from parent to child—for example that a cat's hair color and its tail length are inherited independent of each other—Bateson and Punnett showed that certain genes associated with physical traits can be inherited together, or genetically linked . In 1911, after observing that linked traits could on occasion be inherited separately, Thomas Hunt Morgan suggested that " crossovers " can occur between linked genes, where one of

10187-456: Is no difference between the two parental RNA sequences and the resulting crossover RNA region. Because of this, it is often difficult to determine the location of crossover events between two recombining RNA sequences. In imprecise RNA homologous recombination, the crossover region has some difference with the parental RNA sequences – caused by either addition, deletion, or other modification of nucleotides. The level of precision in crossover

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10354-413: Is one common cause of yield loss Genetic modification of plants that can produce pharmaceuticals (and industrial chemicals), sometimes called pharming , is a rather radical new area of plant breeding. The debate surrounding genetically modified food during the 1990s peaked in 1999 in terms of media coverage and risk perception, and continues today – for example, " Germany has thrown its weight behind

10521-423: Is that the virus is not usually passed on to the progeny, so every plant has to be inoculated. The majority of commercially released transgenic plants are currently limited to plants that have introduced resistance to insect pests and herbicides . Insect resistance is achieved through incorporation of a gene from Bacillus thuringiensis (Bt) that encodes a protein that is toxic to some insects. For example,

10688-430: Is the deliberate interbreeding (crossing) of closely or distantly related individuals to produce new crop varieties or lines with desirable properties. Plants are crossbred to introduce traits / genes from one variety or line into a new genetic background. For example, a mildew -resistant pea may be crossed with a high-yielding but susceptible pea, the goal of the cross being to introduce mildew resistance without losing

10855-440: Is the generation of mutants. The breeder hopes for desirable traits to be bred with other cultivars – a process known as mutation breeding . Classical plant breeders also generate genetic diversity within a species by exploiting a process called somaclonal variation , which occurs in plants produced from tissue culture, particularly plants derived from callus . Induced polyploidy , and the addition or removal of chromosomes using

11022-402: Is the main recombination pathway used in many bacteria to repair double-strand breaks in DNA, and the proteins are found in a broad array of bacteria. These double-strand breaks can be caused by UV light and other radiation , as well as chemical mutagens . Double-strand breaks may also arise by DNA replication through a single-strand nick or gap. Such a situation causes what is known as

11189-488: Is then able to anneal to the other 3' overhang in the damaged chromosome through complementary base pairing. After the strands anneal, a small flap of DNA can sometimes remain. Any such flaps are removed, and the SDSA pathway finishes with the resealing, also known as ligation , of any remaining single-stranded gaps. During mitosis, the major homologous recombination pathway for repairing DNA double-strand breaks appears to be

11356-581: Is to be reconceptualised where in times of climatic change the needs and desires of the individual are reshaped to generate sufficiency for all. The quality of a government can be measured by Government effectiveness index , which relates to political efficacy and state capacity . List of forms of government Plato in his book The Republic (375 BC) divided governments into five basic types (four being existing forms and one being Plato's ideal form, which exists "only in speech"): These five regimes progressively degenerate starting with aristocracy at

11523-421: Is transferred between bacteria through direct cell-to-cell contact, homologous recombination helps integrate foreign DNA into the host genome via the RecBCD pathway. The RecBCD enzyme promotes recombination after DNA is converted from single-strand DNA–in which form it originally enters the bacterium–to double-strand DNA during replication. The RecBCD pathway is also essential for the final phase of transduction ,

11690-421: Is typically the case with majority governments, but even a minority government may consist of just one party unable to find a willing coalition partner at the moment. A state that continuously maintains a single-party government within a (nominally) multiparty system possesses a dominant-party system . In a (nondemocratic) one-party system a single ruling party has the (more-or-less) exclusive right to form

11857-463: Is unique in that it does not require a separate similar or identical molecule of DNA, like the DSBR or SDSA pathways of homologous recombination. Instead, the SSA pathway only requires a single DNA duplex, and uses the repeat sequences as the identical sequences that homologous recombination needs for repair. The pathway is relatively simple in concept: after two strands of the same DNA duplex are cut back around

12024-429: Is when farmers are involved in a crop improvement programme with opportunities to make decisions and contribute to the research process at different stages. Participatory approaches to crop improvement can also be applied when plant biotechnologies are being used for crop improvement. Local agricultural systems and genetic diversity are strengthened by participatory programs, and outcomes are enhanced by farmers knowledge of

12191-562: The Coronavirus 3′ stem-loop II-like motif (s2m) , an RNA motif in 3' untranslated region of viral genome, suggesting that RNA recombination events may have occurred in s2m of SARS-CoV-2. Based on computational analysis of 1319 Australia SARS‐CoV‐2 sequences using Recco algorithm ( https://recco.bioinf.mpi-inf.mpg.de/ ), 29742G("G19"), 29744G("G21"), and 29751G("G28") were predicted as recombination hotspots. The SARS-CoV-2 outbreak in Diamond Princess cruise most likely originated from either

12358-548: The Green Revolution increased crop production in the developing world in the 1960s. Following World War II a number of techniques were developed that allowed plant breeders to hybridize distantly related species, and artificially induce genetic diversity. When distantly related species are crossed, plant breeders make use of a number of plant tissue culture techniques to produce progeny from otherwise fruitless mating. Interspecific and intergeneric hybrids are produced from

12525-662: The Indus Valley civilization , and the Yellow River civilization . One reason that explains the emergence of governments includes agriculture. Since the Neolithic Revolution , agriculture has been an efficient method to create food surplus. This enabled people to specialize in non-agricultural activities. Some of them included being able to rule over others as an external authority. Others included social experimentation with diverse governance models. Both these activities formed

12692-619: The RecBCD pathway of homologous recombination. Breaks that occur on only one of the two DNA strands, known as single-strand gaps, are thought to be repaired by the RecF pathway . Both the RecBCD and RecF pathways include a series of reactions known as branch migration , in which single DNA strands are exchanged between two intercrossed molecules of duplex DNA, and resolution , in which those two intercrossed molecules of DNA are cut apart and restored to their normal double-stranded state. The RecBCD pathway

12859-510: The RecQ helicase unwinds the DNA and the RecJ nuclease degrades the strand with a 5' end, leaving the strand with the 3' end intact. RecA protein binds to this strand and is either aided by the RecF, RecO, and RecR proteins or stabilized by them. The RecA nucleoprotein filament then searches for a homologous DNA and exchanges places with the identical or nearly identical strand in the homologous DNA. Although

13026-399: The cotton bollworm , a common cotton pest, feeds on Bt cotton it will ingest the toxin and die. Herbicides usually work by binding to certain plant enzymes and inhibiting their action. The enzymes that the herbicide inhibits are known as the herbicide's " target site ". Herbicide resistance can be engineered into crops by expressing a version of target site protein that is not inhibited by

13193-548: The nuclease activity of Exo1 and Dna2 allows them to cut the single-stranded DNA produced by Sgs1. The RPA protein, which has high affinity for single-stranded DNA, then binds the 3' overhangs. With the help of several other proteins that mediate the process, the Rad51 protein (and Dmc1 , in meiosis) then forms a filament of nucleic acid and protein on the single strand of DNA coated with RPA. This nucleoprotein filament then begins searching for DNA sequences similar to that of

13360-486: The soybean cyst nematode and was able to increase the proportion of resistant plants from 5% to 40%. The International Center for Agricultural Research in the Dry Areas (ICARDA) evolutionary plant breeding is combined with participatory plant breeding in order to allow farmers to choose which varieties suit their needs in their local environment. An influential 1956 effort by Coit A. Suneson to codify this approach coined

13527-399: The 3' overhang. After finding such a sequence, the single-stranded nucleoprotein filament moves into (invades) the similar or identical recipient DNA duplex in a process called strand invasion . In cells that divide through mitosis, the recipient DNA duplex is generally a sister chromatid, which is identical to the damaged DNA molecule and provides a template for repair. In meiosis, however,

13694-450: The BIR pathway remain unclear. Three proposed mechanisms have strand invasion as an initial step, but they differ in how they model the migration of the D-loop and later phases of recombination. The BIR pathway can also help to maintain the length of telomeres (regions of DNA at the end of eukaryotic chromosomes) in the absence of (or in cooperation with) telomerase . Without working copies of

13861-619: The DNA repair enzyme MRE11 , to initiate DNA repair, within 13 seconds. γH2AX, the phosphorylated form of H2AX is also involved in the early steps leading to chromatin decondensation after DNA double-strand breaks. The histone variant H2AX constitutes about 10% of the H2A histones in human chromatin. γH2AX (H2AX phosphorylated on serine 139) can be detected as soon as 20 seconds after irradiation of cells (with DNA double-strand break formation), and half maximum accumulation of γH2AX occurs in one minute. The extent of chromatin with phosphorylated γH2AX

14028-460: The DSB repair model, including uniform homologous integration of transformed DNA (gene therapy), were first shown in plasmid experiments by Orr-Weaver, Szostak and Rothstein. Researching the plasmid-induced DSB, using γ-irradiation in the 1970s-1980s, led to later experiments using endonucleases (e.g. I-SceI) to cut chromosomes for genetic engineering of mammalian cells, where nonhomologous recombination

14195-425: The DSBR (double-strand break repair) pathway or the SDSA (synthesis-dependent strand annealing) pathway. Homologous recombination that occurs during DNA repair tends to result in non-crossover products, in effect restoring the damaged DNA molecule as it existed before the double-strand break. Homologous recombination is conserved across all three domains of life as well as DNA and RNA viruses , suggesting that it

14362-601: The Holliday junction moves along the linked DNA during the branch migration process. It is in this movement of the Holliday junction that base pairs between the two homologous DNA duplexes are exchanged. To catalyze branch migration, the RuvA protein first recognizes and binds to the Holliday junction and recruits the RuvB protein to form the RuvAB complex. Two sets of the RuvB protein, which each form

14529-536: The RecA protein is essential for transformation in Bacillus subtilis and Streptococcus pneumoniae , and expression of the RecA gene is induced during the development of competence for transformation in these organisms. As part of the transformation process, the RecA protein interacts with entering single-stranded DNA (ssDNA) to form RecA/ssDNA nucleofilaments that scan the resident chromosome for regions of homology and bring

14696-550: The SDSA pathway (rather than the DSBR pathway). The SDSA pathway produces non-crossover recombinants (Figure 5). During meiosis non-crossover recombinants also occur frequently and these appear to arise mainly by the SDSA pathway as well. Non-crossover recombination events occurring during meiosis likely reflect instances of repair of DNA double-strand damages or other types of DNA damages. The single-strand annealing (SSA) pathway of homologous recombination repairs double-strand breaks between two repeat sequences . The SSA pathway

14863-401: The SDSA pathway occurs in cells that divide through mitosis and meiosis and results in non-crossover products. In this model, the invading 3' strand is extended along the recipient DNA duplex by a DNA polymerase, and is released as the Holliday junction between the donor and recipient DNA molecules slides in a process called branch migration . The newly synthesized 3' end of the invading strand

15030-766: The Soviet Union was a centralized autocratic one-party state under Joseph Stalin . Identifying a form of government is also difficult because many political systems originate as socio-economic movements and are then carried into governments by parties naming themselves after those movements; all with competing political ideologies. Experience with those movements in power, and the strong ties they may have to particular forms of government, can cause them to be considered as forms of government in themselves. Other complications include general non-consensus or deliberate " distortion or bias " of reasonable technical definitions of political ideologies and associated forms of governing, due to

15197-594: The United States has been chiefly associated with right-wing politics and the Republican Party . However, during the era of segregation many Southern Democrats were conservatives, and they played a key role in the conservative coalition that controlled Congress from 1937 to 1963. Opinions vary by individuals concerning the types and properties of governments that exist. "Shades of gray" are commonplace in any government and its corresponding classification. Even

15364-429: The activities of associated government officials and candidates for office. In a multiparty system of government, multiple political parties have the capacity to gain control of government offices, typically by competing in elections , although the effective number of parties may be limited. A majority government is a government by one or more governing parties together holding an absolute majority of seats in

15531-500: The addition of a phosphate, Sae2 causes a clean cut to be made near a double-strand break in DNA. It is unclear if the endonuclease responsible for this cut is Sae2 itself or another protein, Mre11 . This allows a protein complex including Mre11, known as the MRX complex , to bind to DNA, and begins a series of protein-driven reactions that exchange material between two DNA molecules. The packaging of eukaryotic DNA into chromatin presents

15698-402: The basis of governments. These governments gradually became more complex as agriculture supported larger and denser populations, creating new interactions and social pressures that the government needed to control. David Christian explains As farming populations gathered in larger and denser communities, interactions between different groups increased and the social pressure rose until, in

15865-586: The break is cut back. This happens in two distinct steps: first the MRX complex recruits the Sae2 protein, and these two proteins trim back the 5' ends on either side of the break to create short 3' overhangs of single-strand DNA; in the second step, 5'→3' resection is continued by the Sgs1 helicase and the Exo1 and Dna2 nucleases. As a helicase , Sgs1 "unzips" the double-strand DNA, while

16032-435: The break is repaired via TMEJ in the S and G 2 phases of the cell cycle. In contrast to homologous recombination and TMEJ, NHEJ is predominant in the G 1 phase of the cell cycle, when the cell is growing but not yet ready to divide. It occurs less frequently after the G 1 phase, but maintains at least some activity throughout the cell cycle. The mechanisms that regulate homologous recombination and NHEJ throughout

16199-471: The break, and aligns them to enable the two complementary repeat sequences to anneal. After annealing is complete, leftover non-homologous flaps of the 3' overhangs are cut away by a set of nucleases, known as Rad1/Rad10 , which are brought to the flaps by the Saw1 and Slx4 proteins. New DNA synthesis fills in any gaps, and ligation restores the DNA duplex as two continuous strands. The DNA sequence between

16366-492: The cell cycle vary widely between species. Cyclin-dependent kinases (CDKs), which modify the activity of other proteins by adding phosphate groups to (that is, phosphorylating ) them, are important regulators of homologous recombination in eukaryotes. When DNA replication begins in budding yeast, the cyclin-dependent kinase Cdc28 begins homologous recombination by phosphorylating the Sae2 protein. After being so activated by

16533-433: The cell cycle, when sister chromatids are more easily available. Compared to homologous chromosomes, which are similar to another chromosome but often have different alleles , sister chromatids are an ideal template for homologous recombination because they are an identical copy of a given chromosome. When no homologous template is available or when the template cannot be accessed due to a defect in homologous recombination,

16700-439: The course of evolution . Homologous recombination is also used in horizontal gene transfer to exchange genetic material between different strains and species of bacteria and viruses. Horizontal gene transfer is the primary mechanism for the spread of antibiotic resistance in bacteria. Although homologous recombination varies widely among different organisms and cell types, for double-stranded DNA ( dsDNA ) most forms involve

16867-409: The course of doing so, narrow down the genetic diversity of that variety to a specific few biotypes. It is practiced worldwide by individuals such as gardeners and farmers, and by professional plant breeders employed by organizations such as government institutions, universities, crop-specific industry associations or research centers. International development agencies believe that breeding new crops

17034-421: The desired traits. Furthermore, two different homozygous plants created in that way can be used to produce a generation of F1 hybrid plants which have the advantages of heterozygosity and a greater range of possible traits. Thus, an individual heterozygous plant chosen for its desirable characteristics can be converted into a heterozygous variety (F1 hybrid) without the necessity of vegetative reproduction but as

17201-412: The double-strand break repair (DSBR) pathway (sometimes called the double Holliday junction model ) and the synthesis-dependent strand annealing (SDSA) pathway. The two pathways are similar in their first several steps. After a double-strand break occurs, the MRX complex ( MRN complex in humans) binds to DNA on either side of the break. Next a resection takes place, in which DNA around the 5' ends of

17368-443: The early 20th century, plant breeders realized that Gregor Mendel 's findings on the non-random nature of inheritance could be applied to seedling populations produced through deliberate pollinations to predict the frequencies of different types. Wheat hybrids were bred to increase the crop production of Italy during the so-called " Battle for Grain " (1925–1940). Heterosis was explained by George Harrison Shull . It describes

17535-1316: The emergence of other models of homologous recombination, called SDSA pathways , which do not always rely on Holliday junctions. Much of the later work identifying proteins involved in the process and determining their mechanisms has been performed by a number of individuals including James Haber , Patrick Sung , Stephen Kowalczykowski , and others. Homologous recombination (HR) is essential to cell division in eukaryotes like plants, animals, fungi and protists. Homologous recombination repairs double-strand breaks in DNA caused by ionizing radiation or DNA-damaging chemicals. Left unrepaired, these double-strand breaks can cause large-scale rearrangement of chromosomes in somatic cells , which can in turn lead to cancer. In addition to repairing DNA, homologous recombination also helps produce genetic diversity when cells divide in meiosis to become specialized gamete cells— sperm or egg cells in animals, pollen or ovules in plants, and spores in fungi . It does so by facilitating chromosomal crossover , in which regions of similar but not identical DNA are exchanged between homologous chromosomes . This creates new, possibly beneficial combinations of genes, which can give offspring an evolutionary advantage. Chromosomal crossover often begins when

17702-466: The entering ssDNA to the corresponding region, where strand exchange and homologous recombination occur. Thus the process of homologous recombination during bacterial transformation has fundamental similarities to homologous recombination during meiosis . Homologous recombination occurs in several groups of viruses. In DNA viruses such as herpesvirus , recombination occurs through a break-and-rejoin mechanism like in bacteria and eukaryotes. There

17869-401: The enzyme telomerase, telomeres typically shorten with each cycle of mitosis, which eventually blocks cell division and leads to senescence . In budding yeast cells where telomerase has been inactivated through mutations, two types of "survivor" cells have been observed to avoid senescence longer than expected by elongating their telomeres through BIR pathways. Maintaining telomere length

18036-570: The framework of representative democracy, but the constitution limits majority rule , usually through the provision by all of certain universal rights , such as freedom of speech or freedom of association . A republic is a form of government in which the country is considered a "public matter" ( Latin : res publica ), not the private concern or property of the rulers, and where offices of states are subsequently directly or indirectly elected or appointed rather than inherited. The people, or some significant portion of them, have supreme control over

18203-811: The functions and number of branches. An independent, parallel distribution of powers between branches of government is the separation of powers . A shared, intersecting, or overlapping distribution of powers is the fusion of powers . Governments are often organised into three branches with separate powers: a legislature, an executive, and a judiciary; this is sometimes called the trias politica model. However, in parliamentary and semi-presidential systems , branches of government often intersect, having shared membership and overlapping functions. Many governments have fewer or additional branches, such as an independent electoral commission or auditory branch. Presently, most governments are administered by members of an explicitly constituted political party which coordinates

18370-419: The future include the lack of arable land, increasingly harsh cropping conditions and the need to maintain food security, which involves being able to provide the world population with sufficient nutrition. Crops need to be able to mature in multiple environments to allow worldwide access, which involves solving problems including drought tolerance. It has been suggested that global solutions are achievable through

18537-577: The general usability of the process across multiple target plant species. These methods will work even better with large, publicly available open data sets . Speed breeding is introduced by Watson et al. 2018. Classical (human performed) phenotyping during speed breeding is also possible, using a procedure developed by Richard et al. 2015. As of 2020 it is highly anticipated that SB and automated phenotyping will, combined, produce greatly improved outcomes – see § Phenotyping and artificial intelligence above. The NGS platform has substantially declined

18704-406: The genome of the new bacterial host. Natural bacterial transformation involves the transfer of DNA from a donor bacterium to a recipient bacterium, where both donor and recipient are ordinarily of the same species . Transformation, unlike bacterial conjugation and transduction, depends on numerous bacterial gene products that specifically interact to perform this process. Thus transformation

18871-628: The government and where offices of state are elected or chosen by elected people. A common simplified definition of a republic is a government where the head of state is not a monarch. Montesquieu included both democracies , where all the people have a share in rule, and aristocracies or oligarchies , where only some of the people rule, as republican forms of government. Other terms used to describe different republics include democratic republic , parliamentary republic , semi-presidential republic , presidential republic , federal republic , people's republic , and Islamic republic . Federalism

19038-401: The government, and the formation of other parties may be obstructed or illegal. In some cases, a government may have a non-partisan system , as is the case with absolute monarchy or non-partisan democracy . Democracy is the most popular form of government. More than half of the nations in the world are democracies—97 of 167, as of 2021. However, the world is becoming more authoritarian with

19205-515: The herbicide. This is the method used to produce glyphosate resistant (" Roundup Ready ") crop plants. Genetic modification can further increase yields by increasing stress tolerance to a given environment. Stresses such as temperature variation, are signalled to the plant via a cascade of signalling molecules which will activate a transcription factor to regulate gene expression . Overexpression of particular genes involved in cold acclimation has been shown to produce more resistance to freezing, which

19372-493: The high-yield characteristics. Progeny from the cross would then be crossed with the high-yielding parent to ensure that the progeny were most like the high-yielding parent, ( backcrossing ). The progeny from that cross would then be tested for yield (selection, as described above) and mildew resistance and high-yielding resistant plants would be further developed. Plants may also be crossed with themselves to produce inbred varieties for breeding. Pollinators may be excluded through

19539-483: The high-yielding parent, the progeny will be crossed back to that parent for several generations (See backcrossing ). This process removes most of the genetic contribution of the mildew resistant parent. Classical breeding is therefore a cyclical process. With classical breeding techniques, the breeder does not know exactly what genes have been introduced to the new cultivars. Some scientists therefore argue that plants produced by classical breeding methods should undergo

19706-449: The homologous chromosome. PRDM9 deposits both H3K4me3 and H3K36me3 histone methylation marks at the sites it binds, and this methyltransferase activity is essential for its role in DSB positioning. Following their formation, DSB sites are processed by resection, resulting in single-stranded DNA (ssDNA) that becomes decorated with DMC1. From mid-zygotene to early pachytene, as part of the recombinational repair process, DMC1 dissociates from

19873-550: The implicit threat of a coup d'état or mass insurrection ). Absolute monarchy is a historically prevalent form of autocracy, wherein a monarch governs as a singular sovereign with no limitation on royal prerogative . Most absolute monarchies are hereditary , however some, notably the Holy See , are elected by an electoral college (such as the college of cardinals , or prince-electors ). Other forms of autocracy include tyranny , despotism , and dictatorship . Aristocracy

20040-530: The late 19th century. Gartons Agricultural Plant Breeders in England was established in the 1890s by John Garton, who was one of the first to commercialize new varieties of agricultural crops created through cross-pollination. The firm's first introduction was the Abundance Oat , an oat variety. It is one of the first agricultural grain varieties bred from a controlled cross, introduced to commerce in 1892. In

20207-511: The linked genes physically crosses over to a different chromosome . Two decades later, Barbara McClintock and Harriet Creighton demonstrated that chromosomal crossover occurs during meiosis , the process of cell division by which sperm and egg cells are made. Within the same year as McClintock's discovery, Curt Stern showed that crossing over—later called "recombination"—could also occur in somatic cells like white blood cells and skin cells that divide through mitosis . In 1947,

20374-479: The literature of classical antiquity , including Plato 's Ship of State . In British English , "government" sometimes refers to what's also known as a " ministry " or an " administration ", i.e., the policies and government officials of a particular executive or governing coalition . Finally, government is also sometimes used in English as a synonym for rule or governance. In other languages, cognates may have

20541-658: The marketplace are both safe and meet farmers' needs. Examples include variety registration, seed schemes, regulatory authorizations for GM plants, etc. Industrial breeding of plants has unintentionally altered how agricultural cultivars associate with their microbiome. In maize, for example, breeding has altered the nitrogen cycling taxa required to the rhizosphere, with more modern lines recruiting less nitrogen fixing taxa and more nitrifiers and denitrifiers . Microbiomes of breeding lines showed that hybrid plants share much of their bacterial community with their parents, such as Cucurbita seeds and apple shoot endophytes. In addition,

20708-463: The marketplace. Even with the very latest in biotech -assisted conventional breeding, incorporation of a trait takes an average of seven generations for clonally propagated crops, nine for self-fertilising , and seventeen for cross-pollinating . Modern plant breeding may use techniques of molecular biology to select, or in the case of genetic modification, to insert, desirable traits into plants. Application of biotechnology or molecular biology

20875-486: The microbiologist Joshua Lederberg showed that bacteria—which had been assumed to reproduce only asexually through binary fission —are capable of genetic recombination, which is more similar to sexual reproduction. This work established E. coli as a model organism in genetics, and helped Lederberg win the 1958 Nobel Prize in Physiology or Medicine . Building on studies in fungi , in 1964 Robin Holliday proposed

21042-524: The most liberal democracies limit rival political activity to one extent or another while the most tyrannical dictatorships must organize a broad base of support thereby creating difficulties for " pigeonholing " governments into narrow categories. Examples include the claims of the United States as being a plutocracy rather than a democracy since some American voters believe elections are being manipulated by wealthy Super PACs . Some consider that government

21209-458: The nature of politics in the modern era. For example: The meaning of "conservatism" in the United States has little in common with the way the word's definition is used elsewhere. As Ribuffo notes, "what Americans now call conservatism much of the world calls liberalism or neoliberalism "; a "conservative" in Finland would be labeled a " socialist " in the United States. Since the 1950s conservatism in

21376-415: The need for breeding multiple generations of plants to get a generation that is homogeneous for the desired traits, thereby saving much time over the natural version of the same process. There are many plant tissue culturing techniques that can be used to achieve haploid plants, but microspore culturing is currently the most promising for producing the largest numbers of them. Genetic modification of plants

21543-799: The next generation than less-adapted individuals. Evolutionary plant breeding has been successfully used by the Nepal National Gene Bank to preserve landrace diversity within Jumli Marshi rice while reducing its susceptibility to blast disease. These practices have also been used in Nepal with bean landraces. In 1929, Harlan and Martini proposed a method of plant breeding with heterogeneous populations by pooling an equal number of F2 seeds obtained from 378 crosses among 28 geographically diverse barley cultivars. In 1938, Harlan and Martini demonstrated evolution by natural selection in mixed dynamic populations as

21710-550: The non- peasant , non-servant, and non- city classes in the feudal system . Democracy is a system of government where citizens exercise power by voting and deliberation . In a direct democracy , the citizenry as a whole directly forms a participatory governing body and vote directly on each issue. In indirect democracy , the citizenry governs indirectly through the selection of representatives or delegates from among themselves, typically by election or, less commonly, by sortition . These select citizens then meet to form

21877-434: The offspring of that organism. Homologous recombination requires incoming DNA to be highly similar to the recipient genome, and so horizontal gene transfer is usually limited to similar bacteria. Studies in several species of bacteria have established that there is a log-linear decrease in recombination frequency with increasing difference in sequence between host and recipient DNA. In bacterial conjugation , where DNA

22044-405: The parliament, in contrast to a minority government in which they have only a plurality of seats and often depend on a confidence-and-supply arrangement with other parties. A coalition government is one in which multiple parties cooperate to form a government as part of a coalition agreement . In a single-party government, a single party forms a government without the support of a coalition, as

22211-458: The people as a whole (a democracy, such as a republic). Thomas Hobbes stated on their classification: The difference of Commonwealths consisteth in the difference of the sovereign , or the person representative of all and every one of the multitude. And because the sovereignty is either in one man, or in an assembly of more than one; and into that assembly either every man hath right to enter, or not everyone, but certain men distinguished from

22378-454: The plant genome by genetic recombination using the bacteria Agrobacterium tumefaciens or A. rhizogenes , or by direct methods like the gene gun or microinjection . Using plant viruses to insert genetic constructs into plants is also a possibility, but the technique is limited by the host range of the virus. For example, Cauliflower mosaic virus (CaMV) only infects cauliflower and related species. Another limitation of viral vectors

22545-443: The plant. A marker for the selection of transformed plants is also included. In the laboratory , antibiotic resistance is a commonly used marker: Plants that have been successfully transformed will grow on media containing antibiotics; plants that have not been transformed will die. In some instances markers for selection are removed by backcrossing with the parent plant prior to commercial release. The construct can be inserted in

22712-432: The power to govern is shared between national and provincial/state governments, creating what is often called a federation . Proponents are often called federalists . Governments are typically organised into distinct institutions constituting branches of government each with particular powers , functions, duties, and responsibilities. The distribution of powers between these institutions differs between governments, as do

22879-573: The process of plant breeding, with its ability to select specific genes allowing crops to perform at a level which yields the desired results. One issue facing agriculture is the loss of landraces and other local varieties which have diversity that may have useful genes for climate adaptation in the future. Conventional breeding intentionally limits phenotype plasticity within genotypes and limits variability between genotypes. Uniformity does not allow crops to adapt to climate change and other biotic stresses and abiotic stresses . Plant breeders' rights

23046-593: The proportional contribution of the microbiome from parents to offspring corresponds to the amount of genetic material contributed by each parent during breeding and domestication. As of 2020 machine learning – and especially deep machine learning – has recently become more commonly used in phenotyping . Computer vision using ML has made great strides and is now being applied to leaf phenotyping and other phenotyping jobs typically performed by human eyes. Pound et al. 2017 and Singh et al. 2016 are especially salient examples of early successful application and demonstration of

23213-541: The proteins and specific mechanisms involved in their initial phases differ, the two pathways are similar in that they both require single-stranded DNA with a 3' end and the RecA protein for strand invasion. The pathways are also similar in their phases of branch migration , in which the Holliday junction slides in one direction, and resolution , in which the Holliday junctions are cleaved apart by enzymes. The alternative, non-reciprocal type of resolution may also occur by either pathway. Immediately after strand invasion,

23380-414: The quality required and evaluation of the target environment. A 2019 review of participatory plant breeding indicated that it had not gained widespread acceptance despite its record of successfully developing varieties with improved diversity and nutritional quality, as well as greater likelihood of these improved varieties being adopted by farmers. This review also found participatory plant breeding to have

23547-405: The recipient DNA tends to be from a similar but not necessarily identical homologous chromosome. A displacement loop ( D-loop ) is formed during strand invasion between the invading 3' overhang strand and the homologous chromosome. After strand invasion, a DNA polymerase extends the end of the invading 3' strand by synthesizing new DNA. This changes the D-loop to a cross-shaped structure known as

23714-447: The repeats is always lost, as is one of the two repeats. The SSA pathway is considered mutagenic since it results in such deletions of genetic material. During DNA replication , double-strand breaks can sometimes be encountered at replication forks as DNA helicase unzips the template strand. These defects are repaired in the break-induced replication (BIR) pathway of homologous recombination. The precise molecular mechanisms of

23881-455: The rest; it is manifest there can be but three kinds of Commonwealth. For the representative must need to be one man or more; and if more, then it is the assembly of all, or but of a part. When the representative is one man, then is the Commonwealth a monarchy; when an assembly of all that will come together, then it is a democracy or popular Commonwealth; when an assembly of a part only, then it

24048-433: The result of the cross of two homozygous/doubled haploid lines derived from the originally selected plant. This shortcut has been dubbed 'reverse breeding'. Plant tissue culturing can produce haploid or double haploid plant lines and generations. This cuts down the genetic diversity taken from that plant species in order to select for desirable traits that will increase the fitness of the individuals. Using this method decreases

24215-448: The same basic steps. After a double-strand break occurs, sections of DNA around the 5' ends of the break are cut away in a process called resection . In the strand invasion step that follows, an overhanging 3' end of the broken DNA molecule then "invades" a similar or identical DNA molecule that is not broken. After strand invasion, the further sequence of events may follow either of two main pathways discussed below (see Models );

24382-800: The same host cell, homologous recombination can allow those two viruses to swap genes and thereby evolve more potent variations of themselves. Homologous recombination is the proposed mechanism whereby the DNA virus human herpesvirus-6 integrates into human telomeres. When two or more viruses, each containing lethal genomic damage, infect the same host cell, the virus genomes can often pair with each other and undergo homologous recombinational repair to produce viable progeny. This process, known as multiplicity reactivation, has been studied in several bacteriophages , including phage T4 . Enzymes employed in recombinational repair in phage T4 are functionally homologous to enzymes employed in bacterial and eukaryotic recombinational repair. In particular, with regard to

24549-707: The same infected cell. RNA recombination appears to be a major driving force in determining (1) genetic variability within a CoV species, (2) the capability of a CoV species to jump from one host to another, and (3) infrequently, the emergence of novel CoVs. The mechanism of recombination in CoVs likely involves template switching during genome replication. Recombination in RNA viruses appears to be an adaptation for coping with genome damage. The pandemic SARS-CoV-2's entire receptor binding motif appears to have been introduced through recombination from coronaviruses of pangolins . Such

24716-405: The same safety testing regime as genetically modified plants. There have been instances where plants bred using classical techniques have been unsuitable for human consumption, for example the poison solanine was unintentionally increased to unacceptable levels in certain varieties of potato through plant breeding. New potato varieties are often screened for solanine levels before reaching

24883-433: The same. If a gene's location and function is identified in one plant species, a very similar gene likely can also be found in a similar location in another related species genome. Homozygous plants with desirable traits can be produced from heterozygous starting plants, if a haploid cell with the alleles for those traits can be produced, and then used to make a doubled haploid . The doubled haploid will be homozygous for

25050-436: The site of recombination. Patch products, on the other hand, are non-crossover products in which there is no such rearrangement and there is only a "patch" of hybrid DNA in the recombination product. Homologous recombination is an important method of integrating donor DNA into a recipient organism's genome in horizontal gene transfer , the process by which an organism incorporates foreign DNA from another organism without being

25217-475: The site of the double-strand break, the two resulting 3' overhangs then align and anneal to each other, restoring the DNA as a continuous duplex. As DNA around the double-strand break is cut back, the single-stranded 3' overhangs being produced are coated with the RPA protein, which prevents the 3' overhangs from sticking to themselves. A protein called Rad52 then binds each of the repeat sequences on either side of

25384-605: The south of France , are now grown in southern Germany. Plant breeding started with sedentary agriculture and particularly the domestication of the first agricultural plants, a practice which is estimated to date back 9,000 to 11,000 years. Initially early farmers simply selected food plants with particular desirable characteristics, and employed these as progenitors for subsequent generations, resulting in an accumulation of valuable traits over time. Grafting technology had been practiced in China before 2000 BCE. By 500 BCE grafting

25551-460: The ssDNA and counts decrease until all breaks (except those on the XY chromosomes) are repaired at late pachytene. Several other proteins are involved in this process, including ZCWPW1, the first protein directly positioned by PRDM9's dual histone marks. ZCWPW1 is important for homologous DSB repair, not positioning. Two primary models for how homologous recombination repairs double-strand breaks in DNA are

25718-494: The surface of RuvA as they are guided by the protein from one duplex to the other. In the resolution phase of recombination, any Holliday junctions formed by the strand invasion process are cut, thereby restoring two separate DNA molecules. This cleavage is done by RuvAB complex interacting with RuvC, which together form the RuvABC complex. RuvC is an endonuclease that cuts the degenerate sequence 5'-(A/T)TT(G/C)-3'. The sequence

25885-570: The tendency of the progeny of a specific cross to outperform both parents. The detection of the usefulness of heterosis for plant breeding has led to the development of inbred lines that reveal a heterotic yield advantage when they are crossed. Maize was the first species where heterosis was widely used to produce hybrids. Statistical methods were also developed to analyze gene action and distinguish heritable variation from variation caused by environment. In 1933 another important breeding technique, cytoplasmic male sterility (CMS), developed in maize,

26052-586: The term evolutionary plant breeding and concluded that 15 generations of natural selection are desirable to produce results that are competitive with conventional breeding. Evolutionary breeding allows working with much larger plant population sizes than conventional breeding. It has also been used in tandem with conventional practices in order to develop both heterogeneous and homogeneous crop lines for low input agricultural systems that have unpredictable stress conditions. Evolutionary plant breeding has been delineated into four stages: Issues facing plant breeding in

26219-476: The time and cost required for sequencing and facilitated SNP discovery in model and non-model plants. This in turn has led to employing large-scale SNP markers in genomic selection approaches which aim at predicting genomic breeding values/GEBVs of genotypes in a given population. This method can increase the selection accuracy and decrease the time of each breeding cycle. It has been used in different crops such as maize, wheat, etc. Participatory plant breeding (PPB)

26386-401: The top and tyranny at the bottom. In his Politics , Aristotle elaborates on Plato's five regimes discussing them in relation to the government of one, of the few, and of the many. From this follows the classification of forms of government according to which people have the authority to rule: either one person (an autocracy , such as monarchy), a select group of people (an aristocracy), or

26553-529: The use of pollination bags . Classical breeding relies largely on homologous recombination between chromosomes to generate genetic diversity . The classical plant breeder may also make use of a number of in vitro techniques such as protoplast fusion , embryo rescue or mutagenesis (see below) to generate diversity and produce hybrid plants that would not exist in nature . Traits that breeders have tried to incorporate into crop plants include: Successful commercial plant breeding concerns were founded from

26720-403: The visual identification of the expressed trait in the plant. The purpose of marker assisted selection, or plant genome analysis, is to identify the location and function ( phenotype ) of various genes within the genome. If all of the genes are identified it leads to genome sequence . All plants have varying sizes and lengths of genomes with genes that code for different proteins, but many are also

26887-471: The word government is often used more specifically to refer to the approximately 200 independent national governments on Earth, as well as their subsidiary organizations, such as state and provincial governments as well as local governments . The word government derives from the Greek verb κυβερνάω [ kubernáo ] meaning to steer with a gubernaculum (rudder), the metaphorical sense being attested in

27054-412: Was described by Marcus Morton Rhoades . CMS is a maternally inherited trait that makes the plant produce sterile pollen . This enables the production of hybrids without the need for labor-intensive detasseling . These early breeding techniques resulted in large yield increase in the United States in the early 20th century. Similar yield increases were not produced elsewhere until after World War II ,

27221-464: Was not involved in strand invasion) also forms a Holliday junction with the homologous chromosome. The double Holliday junctions are then converted into recombination products by nicking endonucleases , a type of restriction endonuclease which cuts only one DNA strand. The DSBR pathway commonly results in crossover, though it can sometimes result in non-crossover products; the ability of a broken DNA molecule to collect sequences from separated donor loci

27388-462: Was shown in mitotic budding yeast using plasmids or endonuclease induction of chromosomal events. Because of this tendency for chromosomal crossover, the DSBR pathway is a likely model of how crossover homologous recombination occurs during meiosis. Whether recombination in the DSBR pathway results in chromosomal crossover is determined by how the double Holliday junction is cut, or "resolved". Chromosomal crossover will occur if one Holliday junction

27555-496: Was the first large country to have a Communist government. Since the fall of the Berlin Wall , liberal democracy has become an even more prevalent form of government. In the nineteenth and twentieth centuries, there was a significant increase in the size and scale of government at the national level. This included the regulation of corporations and the development of the welfare state . In political science, it has long been

27722-441: Was used to double the number of chromosomes in the cell and thus allow the production of a fertile line. Failure to produce a hybrid may be due to pre- or post- fertilization incompatibility. If fertilization is possible between two species or genera, the hybrid embryo may abort before maturation. If this does occur the embryo resulting from an interspecific or intergeneric cross can sometimes be rescued and cultured to produce

27889-436: Was well established and practiced. Gregor Mendel (1822–84) is considered the "father of genetics ". His experiments with plant hybridization led to his establishing laws of inheritance . Genetics stimulated research to improve crop production through plant breeding. Selective breeding played a crucial role in the Green Revolution of the 20th century. Modern plant breeding is applied genetics, but its scientific basis

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