1.
Chromosome
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A chromosome is a DNA molecule with part or all of the genetic material of an organism. Prokaryotes usually have one single circular chromosome, whereas most eukaryotes are diploid, chromosomes in eukaryotes are composed of chromatin fiber. Chromatin fiber is made of nucleosomes, a nucleosome is a histone octamer with part of a longer DNA strand attached to and wrapped around it. Chromatin fiber, together with associated proteins is known as chromatin, chromatin is present in most cells, with a few exceptions, for example, red blood cells. Occurring only in the nucleus of cells, chromatin contains the vast majority of DNA, except for a small amount inherited maternally. Chromosomes are normally visible under a microscope only when the cell is undergoing the metaphase of cell division. Before this happens every chromosome is copied once, and the copy is joined to the original by a centromere resulting in an X-shaped structure, the original chromosome and the copy are now called sister chromatids. During metaphase, when a chromosome is in its most condensed state, in this highly condensed form chromosomes are easiest to distinguish and study. In prokaryotic cells, chromatin occurs free-floating in cytoplasm, as these cells lack organelles, the main information-carrying macromolecule is a single piece of coiled double-helix DNA, containing many genes, regulatory elements and other noncoding DNA. The DNA-bound macromolecules are proteins that serve to package the DNA, chromosomes vary widely between different organisms. Some species such as certain bacteria also contain plasmids or other extrachromosomal DNA and these are circular structures in the cytoplasm that contain cellular DNA and play a role in horizontal gene transfer. Chromosomal recombination during meiosis and subsequent sexual reproduction plays a significant role in genetic diversity. In prokaryotes and viruses, the DNA is often densely packed and organized, in the case of archaea, by homologs to eukaryotic histones, small circular genomes called plasmids are often found in bacteria and also in mitochondria and chloroplasts, reflecting their bacterial origins. Some use the term chromosome in a sense, to refer to the individualized portions of chromatin in cells. However, others use the concept in a sense, to refer to the individualized portions of chromatin during cell division. The word chromosome comes from the Greek χρῶμα and σῶμα, describing their strong staining by particular dyes, schleiden, Virchow and Bütschli were among the first scientists who recognized the structures now so familiar to everyone as chromosomes. The term was coined by von Waldeyer-Hartz, referring to the term chromatin, in a series of experiments beginning in the mid-1880s, Theodor Boveri gave the definitive demonstration that chromosomes are the vectors of heredity. His two principles were the continuity of chromosomes and the individuality of chromosomes and it is the second of these principles that was so original
2.
Homology (biology)
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In biology, homology is the existence of shared ancestry between a pair of structures, or genes, in different taxa. Evolutionary biology explains homologous structures adapted to different purposes as the result of descent with modification from a common ancestor, examples include the legs of a centipede, the maxillary palp and labial palp of an insect, and the spinous processes of successive vertebrae in a vertebral column. Sequence homology between protein or DNA sequences is defined in terms of shared ancestry. Two segments of DNA can have shared ancestry because of either an event or a duplication event. Homology among proteins or DNA is inferred from their sequence similarity, significant similarity is strong evidence that two sequences are related by divergent evolution from a common ancestor. Alignments of multiple sequences are used to discover the homologous regions, the word homology, coined in about 1656, derives from the Greek ὁμόλογος homologos from ὁμός homos same and λόγος logos relation. Homology is the relationship between biological structures or sequences that are derived from a common ancestor, for example, many insects possess two pairs of flying wings. In beetles, the first pair of wings has evolved into a pair of hard wing covers, the same major forearm bones are found in fossils of lobe-finned fish such as Eusthenopteron. The opposite of homologous organs are analogous organs which do similar jobs in two taxa that were not present in their last common ancestor but rather evolved separately. For example, the wings of insects and birds evolved independently in widely separated groups, similarly, the wings of a sycamore maple seed and the wings of a bird are analogous but not homologous, as they develop from quite different structures. A structure can be homologous at one level, but only analogous at another, for example, in the pterosaurs, the wing involves both the forelimb and the hindlimb. Analogy is called homoplasy in cladistics, and convergent or parallel evolution in evolutionary biology, specialised terms are used in taxonomic research. Primary homology is that initially conjectured by a researcher based on similar structure or anatomical connections, secondary homology is implied by parsimony analysis, where a character that only occurs once on a tree is taken to be homologous. As implied in this definition, many cladists consider homology to be synonymous with synapomorphy, homologies provide the fundamental basis for all biological classification, although some may be highly counter-intuitive. The homologies between these have been discovered by comparing genes in evolutionary developmental biology, among insects, the stinger of the female honey bee is a modified ovipositor, homologous with ovipositors in other insects such as the Orthoptera, Hemiptera, and those Hymenoptera without stingers. The three small bones in the ear of mammals including humans, the malleus, incus. The malleus and incus develop in the embryo from structures that form jaw bones in lizards, both lines of evidence show that these bones are homologous, sharing a common ancestor. Among the many homologies in mammal reproductive systems, ovaries and testicles are homologous, in many plants, defensive or storage structures are made by modifications of the development of primary leaves, stems, and roots
3.
United States National Library of Medicine
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The United States National Library of Medicine, operated by the United States federal government, is the worlds largest medical library. Located in Bethesda, Maryland, the NLM is an institute within the National Institutes of Health, the current director of the NLM is Patricia Flatley Brennan. Since 1879, the National Library of Medicine has published the Index Medicus and these resources are accessible without charge on the internet. S. and international consultants. The Extramural Division provides grants to research in medical information science and to support planning and development of computer. Research, publications, and exhibitions on the history of medicine, in April 2008 the current exhibition Against the Odds, Making a Difference in Global Health was launched. For details of the history of the Library, see Library of the Surgeon Generals Office. The precursor of the National Library of Medicine, established in 1836, was the Library of the Surgeon Generals Office, the Armed Forces Institute of Pathology and its Medical Museum were founded in 1862 as the Army Medical Museum. Throughout their history the Library of the Surgeon Generals Office and the Army Medical Museum often shared quarters, from 1866 to 1887, they were housed in Fords Theatre after production there was stopped, following the assassination of President Abraham Lincoln. In 1956, the collection was transferred from the control of the U. S. The library moved to its current quarters in Bethesda, Maryland, on the campus of the National Institutes of Health, journalReview. org National Library of Medicine classification system PubMed Miles, Wyndham D. A History of the National Library of Medicine, The Nations Treasury of Medical Knowledge
4.
Protein
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Proteins are large biomolecules, or macromolecules, consisting of one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, responding to stimuli, a linear chain of amino acid residues is called a polypeptide. A protein contains at least one long polypeptide, short polypeptides, containing less than 20–30 residues, are rarely considered to be proteins and are commonly called peptides, or sometimes oligopeptides. The individual amino acid residues are bonded together by peptide bonds, the sequence of amino acid residues in a protein is defined by the sequence of a gene, which is encoded in the genetic code. In general, the code specifies 20 standard amino acids, however. Sometimes proteins have non-peptide groups attached, which can be called prosthetic groups or cofactors, proteins can also work together to achieve a particular function, and they often associate to form stable protein complexes. Once formed, proteins only exist for a period of time and are then degraded and recycled by the cells machinery through the process of protein turnover. A proteins lifespan is measured in terms of its half-life and covers a wide range and they can exist for minutes or years with an average lifespan of 1–2 days in mammalian cells. Abnormal and or misfolded proteins are degraded more rapidly due to being targeted for destruction or due to being unstable. Like other biological macromolecules such as polysaccharides and nucleic acids, proteins are essential parts of organisms, many proteins are enzymes that catalyse biochemical reactions and are vital to metabolism. Proteins also have structural or mechanical functions, such as actin and myosin in muscle and the proteins in the cytoskeleton, other proteins are important in cell signaling, immune responses, cell adhesion, and the cell cycle. In animals, proteins are needed in the diet to provide the essential amino acids that cannot be synthesized, digestion breaks the proteins down for use in the metabolism. Methods commonly used to study structure and function include immunohistochemistry, site-directed mutagenesis, X-ray crystallography, nuclear magnetic resonance. Most proteins consist of linear polymers built from series of up to 20 different L-α-amino acids, all proteinogenic amino acids possess common structural features, including an α-carbon to which an amino group, a carboxyl group, and a variable side chain are bonded. Only proline differs from this structure as it contains an unusual ring to the N-end amine group. The amino acids in a chain are linked by peptide bonds. Once linked in the chain, an individual amino acid is called a residue, and the linked series of carbon, nitrogen. The peptide bond has two forms that contribute some double-bond character and inhibit rotation around its axis, so that the alpha carbons are roughly coplanar
5.
Public domain
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The term public domain has two senses of meaning. Anything published is out in the domain in the sense that it is available to the public. Once published, news and information in books is in the public domain, in the sense of intellectual property, works in the public domain are those whose exclusive intellectual property rights have expired, have been forfeited, or are inapplicable. Examples for works not covered by copyright which are therefore in the domain, are the formulae of Newtonian physics, cooking recipes. Examples for works actively dedicated into public domain by their authors are reference implementations of algorithms, NIHs ImageJ. The term is not normally applied to situations where the creator of a work retains residual rights, as rights are country-based and vary, a work may be subject to rights in one country and be in the public domain in another. Some rights depend on registrations on a basis, and the absence of registration in a particular country, if required. Although the term public domain did not come into use until the mid-18th century, the Romans had a large proprietary rights system where they defined many things that cannot be privately owned as res nullius, res communes, res publicae and res universitatis. The term res nullius was defined as not yet appropriated. The term res communes was defined as things that could be enjoyed by mankind, such as air, sunlight. The term res publicae referred to things that were shared by all citizens, when the first early copyright law was first established in Britain with the Statute of Anne in 1710, public domain did not appear. However, similar concepts were developed by British and French jurists in the eighteenth century, instead of public domain they used terms such as publici juris or propriété publique to describe works that were not covered by copyright law. The phrase fall in the domain can be traced to mid-nineteenth century France to describe the end of copyright term. In this historical context Paul Torremans describes copyright as a coral reef of private right jutting up from the ocean of the public domain. Because copyright law is different from country to country, Pamela Samuelson has described the public domain as being different sizes at different times in different countries. According to James Boyle this definition underlines common usage of the public domain and equates the public domain to public property. However, the usage of the public domain can be more granular. Such a definition regards work in copyright as private property subject to fair use rights, the materials that compose our cultural heritage must be free for all living to use no less than matter necessary for biological survival
6.
Gene
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A gene is a locus of DNA which is made up of nucleotides and is the molecular unit of heredity. The transmission of genes to an offspring is the basis of the inheritance of phenotypic traits. These genes make up different DNA sequences called genotypes, genotypes along with environmental and developmental factors determine what the phenotypes will be. Most biological traits are under the influence of polygenes as well as gene–environment interactions, genes can acquire mutations in their sequence, leading to different variants, known as alleles, in the population. These alleles encode slightly different versions of a protein, which cause different phenotypical traits, usage of the term having a gene typically refers to containing a different allele of the same, shared gene. Genes evolve due to natural selection or survival of the fittest of the alleles, the concept of a gene continues to be refined as new phenomena are discovered. For example, regulatory regions of a gene can be far removed from its coding regions, some viruses store their genome in RNA instead of DNA and some gene products are functional non-coding RNAs. The existence of discrete inheritable units was first suggested by Gregor Mendel, from 1857 to 1864, in Brno, he studied inheritance patterns in 8000 common edible pea plants, tracking distinct traits from parent to offspring. He described these mathematically as 2n combinations where n is the number of differing characteristics in the original peas, although he did not use the term gene, he explained his results in terms of discrete inherited units that give rise to observable physical characteristics. This description prefigured the distinction between genotype and phenotype, charles Darwin developed a theory of inheritance he termed pangenesis, from Greek pan and genesis / genos. Darwin used the term gemmule to describe hypothetical particles that would mix during reproduction, de Vries called these units pangenes, after Darwins 1868 pangenesis theory. In 1909 the Danish botanist Wilhelm Johannsen shortened the name to gene, advances in understanding genes and inheritance continued throughout the 20th century. Deoxyribonucleic acid was shown to be the repository of genetic information by experiments in the 1940s to 1950s. In the early 1950s the prevailing view was that the genes in a chromosome acted like discrete entities, indivisible by recombination, collectively, this body of research established the central dogma of molecular biology, which states that proteins are translated from RNA, which is transcribed from DNA. This dogma has since shown to have exceptions, such as reverse transcription in retroviruses. The modern study of genetics at the level of DNA is known as molecular genetics, in 1972, Walter Fiers and his team at the University of Ghent were the first to determine the sequence of a gene, the gene for Bacteriophage MS2 coat protein. The subsequent development of chain-termination DNA sequencing in 1977 by Frederick Sanger improved the efficiency of sequencing, an automated version of the Sanger method was used in early phases of the Human Genome Project. The theories developed in the 1930s and 1940s to integrate molecular genetics with Darwinian evolution are called the evolutionary synthesis
7.
Wikidata
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Wikidata is a collaboratively edited knowledge base operated by the Wikimedia Foundation. It is intended to provide a source of data which can be used by Wikimedia projects such as Wikipedia. This is similar to the way Wikimedia Commons provides storage for files and access to those files for all Wikimedia projects. Wikidata is powered by the software Wikibase, Wikidata is a document-oriented database, focused on items. Each item represents a topic and is identified by a number, prefixed with the letter Q—for example. This enables the basic information required to identify the topic the item covers to be translated without favouring any language, information is added to items by creating statements. Statements take the form of pairs, with each statement consisting of a property. The creation of the project was funded by donations from the Allen Institute for Artificial Intelligence, the Gordon and Betty Moore Foundation, at this time, only the first phase was available. Historically, a Wikipedia article would include a list of links, being links to articles on the same topic in other editions of Wikipedia. Initially, Wikidata was a repository of interlanguage links. No Wikipedia language editions were able to access Wikidata, so they needed to continue to maintain their own lists of interlanguage links, on 14 January 2013, the Hungarian Wikipedia became the first to enable the provision of interlanguage links via Wikidata. This functionality was extended to the Hebrew and Italian Wikipedias on 30 January, to the English Wikipedia on 13 February, on 23 September 2013, phase 1 went live on Wikimedia Commons. The first aspects of the second phase were deployed on 4 February 2013, the values were initially limited to two data types, with more data types to follow later. The first new type, string, was deployed on 6 March, the ability of the various language editions of Wikipedia to access data added to Wikidata as part of phase two was rolled out progressively between 27 March and 25 April 2013. On 16 September 2015, Wikidata began allowing so-called arbitrary access, for example, in the past the article about Berlin you could not access data about Germany, but with arbitrary access it could. On 27 April 2016 arbitrary access was activated on Wikimedia Commons, phase 3 will involve database querying and the creation of lists based on data stored on Wikidata. As of October 2016 two tools for querying Wikidata were available, AutoList and PetScan, additionally to a public SPARQL endpoint, there is concern that the project is being influenced by lobbying companies, PR professionals and search engine optimizers. As of December 2015, according to Wikimedia statistics, half of the information in Wikidata is unsourced, another 30% is labeled as having come from Wikipedia, but with no indication as to which article
8.
Chromosome 15 (human)
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Chromosome 15 is one of the 23 pairs of chromosomes in humans. People normally have two copies of this chromosome, chromosome 15 spans about 101 million base pairs and represents between 3% and 3. 5% of the total DNA in cells. Identifying genes on each chromosome is an area of genetic research. Because researchers use different approaches to genome annotation their predictions of the number of genes on each chromosome varies, in January 2017, two estimates differed by 10%, with one estimate giving 1,814 genes, and the other estimate giving 1,796 genes. The human leukocyte antigen gene for β2-microglobulin is found at chromosome 15, two of the conditions involve a loss of gene activity in the same part of chromosome 15, the 15q11. 2-q13.1 region. This discovery provided the first evidence in humans that something beyond genes could determine how the genes are expressed, the main characteristics of Angelman syndrome are severe mental retardation, ataxia, lack of speech, and excessively happy demeanor. Angelman syndrome results from a loss of activity in a specific part of chromosome 15. This region contains a gene called UBE3A that, when mutated or absent, people normally have two copies of the UBE3A gene, one from each parent. Both copies of this gene are active in many of the bodys tissues, in the brain, however, only the copy inherited from a persons mother is active. If the maternal copy is lost because of a change or a gene mutation. In most cases, people with Angelman syndrome have a deletion in the copy of chromosome 15. This chromosomal change deletes the region of chromosome 15 that includes the UBE3A gene, in 3% to 7% of cases, Angelman syndrome occurs when a person has two copies of the paternal chromosome 15 instead of one copy from each parent. This phenomenon is called paternal uniparental disomy, people with paternal UPD for chromosome 15 have two copies of the UBE3A gene, but they are both inherited from the father and are therefore inactive in the brain. In a small percentage of cases, Angelman syndrome may be caused by a chromosomal rearrangement called a translocation or by a mutation in a other than UBE3A. These genetic changes can abnormally inactivate the UBE3A gene, Angelman syndrome can be hereditary, as evidenced by one case where a patient became pregnant with a daughter who also had the condition. The main characteristics of this condition include polyphagia, mild to moderate developmental delay, hypogonadism resulting in delayed to no puberty, Prader-Willi syndrome is caused by the loss of active genes in a specific part of chromosome 15, the 15q11-q13 region. People normally have two copies of this chromosome in each cell, one copy from each parent, Prader-Willi syndrome occurs when the paternal copy is partly or entirely missing. In about 70% of cases, Prader-Willi syndrome occurs when the 15q11-q13 region of the paternal chromosome 15 is deleted, the genes in this region are normally active on the paternal copy of the chromosome and are inactive on the maternal copy
9.
Transcription factor
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In molecular biology, a transcription factor is a protein that controls the rate of transcription of genetic information from DNA to messenger RNA, by binding to a specific DNA sequence. In turn, this helps to regulate the expression of genes near that sequence, transcription factors work alone or with other proteins in a complex, by promoting, or blocking the recruitment of RNA polymerase to specific genes. A defining feature of transcription factors is that they contain at least one DNA-binding domain, transcription factors are usually classified into different families based on their DBDs. Transcription factors are essential for the regulation of expression and are, as a consequence. The number of factors found within an organism increases with genome size. Therefore, approximately 10% of genes in the code for transcription factors. Hence, the use of a subset of the approximately 2000 human transcription factors easily accounts for the unique regulation of each gene in the human genome during development. Transcription factors bind to either enhancer or promoter regions of DNA adjacent to the genes that they regulate, depending on the transcription factor, the transcription of the adjacent gene is either up- or down-regulated. Transcription factors use a variety of mechanisms for the regulation of gene expression and these mechanisms include, stabilize or block the binding of RNA polymerase to DNA catalyze the acetylation or deacetylation of histone proteins. The transcription factor can either do this directly or recruit other proteins with this catalytic activity and they bind to the DNA and help initiate a program of increased or decreased gene transcription. As such, they are vital for important cellular processes. Many of these GTFs do not actually bind DNA, but rather are part of the large transcription preinitiation complex that interacts with RNA polymerase directly, the most common GTFs are TFIIA, TFIIB, TFIID, TFIIE, TFIIF, and TFIIH. The preinitiation complex binds to regions of DNA upstream to the gene that they regulate. Other transcription factors regulate the expression of various genes by binding to enhancer regions of DNA adjacent to regulated genes. These transcription factors are critical to making sure that genes are expressed in the cell at the right time and in the right amount. Many transcription factors in multicellular organisms are involved in development, the Hox transcription factor family, for example, is important for proper body pattern formation in organisms as diverse as fruit flies to humans. Another example is the transcription factor encoded by the Sex-determining Region Y gene, cells can communicate with each other by releasing molecules that produce signaling cascades within another receptive cell. If the signal requires upregulation or downregulation of genes in the recipient cell, the estrogen receptor then goes to the cells nucleus and binds to its DNA-binding sites, changing the transcriptional regulation of the associated genes
10.
GeneCards
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GeneCards is a database of human genes that provides genomic, proteomic, transcriptomic, genetic and functional information on all known and predicted human genes. It is being developed and maintained by the Crown Human Genome Center at the Weizmann Institute of Science and this database aims at providing a quick overview of the current available biomedical information about the searched gene, including the human genes, the encoded proteins, and the relevant diseases. The GeneCards database provides access to free Web resources about more than 7000 all known human genes that integrated from >90 data resources, such as HGNC, Ensembl, the core gene list is based on approved gene symbols published by the HUGO Gene Nomenclature Committee. The information are carefully gathered and selected from these databases by the powerful, over time, the GeneCards database has developed a suite of tools that has more specialised capability. Since 1998, the GeneCards database has been used by bioinformatics, genomics. Since the 1980s, sequence information has become abundant, many laboratories realized this. However, the information provided by the sequence databases focus on different aspect. To gather these scattered data, The Weizmann Institute of Science Crown Human Genome Centre developed a database called ‘GeneCards’ in 1997 and this database mainly deals with the human genome information, human genes, the encoded proteins’ functions, and the related diseases. At first, it includes two main features, the function to get integrated biomedical information about certain gene in ‘card’ format. Currently, the version 3 gather information from more than 90 database resources based on a consolidated gene list and it has developed a set of GeneCards suit, which are focus one more specific purposes. Nearly every 3 years life cycle, a new planning phase for subsequent revision will start, including implementation, development and semi-automated quality assurance, and deployment. Technologies used include Eclipse, Apache, Perl, XML, PHP, Propel, Java, R and MySQL. genecards. org/, annotation combinatory, Using GeneDecks, one can get a set of similar genes for a particular gene with a selected combinatorial annotation. The summary table result in ranking the different level of similarity between the genes and the probe gene. Annotation unification, Different data source often offer annotations with heterogeneous naming system, annotation unification of GeneDecks is based on the similarity in GeneCards gene-content space detection algorithms. Partner hunting, In GeneDecks’s Partner Hunter, users give a query gene, Set distillation, In Set distiller, users give a set of genes, and the system ranks attributes by their degree of sharing within a given gene set. GeneALaCart is a gene-set-orientated batch-querying engine based on the popular GeneCards database and it allows retrieval of information about multiple genes in a batch query. The GeneLoc suit member presents a human chromosome map, which is very important for designing a custom-made capture chip. GeneLoc includes further links to GeneCards, NCBIs Human Genome Sequencing, UniGene, firstly, enter what you want to search into the blank on the homepages
11.
Locus (genetics)
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A locus in genetics is the position on a chromosome. Each chromosome carries many genes, humans estimated haploid protein coding genes are 19, 000-20,000, a variant of the similar DNA sequence located at a given locus is called an allele. The ordered list of known for a particular genome is called a gene map. Gene mapping is the process of determining the locus for a biological trait. The chromosomal locus of a gene might be written 3p22.1, here 3 means chromosome 3, p means p-arm. And 22 refers to region 2, band 2 and this is read as two two, not as twenty-two. So the entire locus is read as three P two two point one, the cytogenetic bands are counting from the centromere out toward the telomeres. A range of loci is specified in a similar way. For example, the locus of gene OCA1 may be written 11q1. 4-q2.1, meaning it is on the arm of chromosome 11. The ends of a chromosome are labeled pter and qter, a centisome is defined as 1% of a chromosome length. Chromosomal translocation Cytogenetic notation Karyotype Null allele Michael, R. Cummings, belmont, California, Brooks/Cole Overview at ornl. gov Chromosome Banding and Nomenclature from NCBI
12.
Base pair
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A base pair is a unit consisting of two nucleobases bound to each other by hydrogen bonds. They form the blocks of the DNA double helix. Dictated by specific hydrogen bonding patterns, Watson-Crick base pairs allow the DNA helix to maintain a regular helical structure that is dependent on its nucleotide sequence. The complementary nature of this structure provides a backup copy of all genetic information encoded within double-stranded DNA. Many DNA-binding proteins can recognize specific base pairing patterns that identify particular regulatory regions of genes, intramolecular base pairs can occur within single-stranded nucleic acids. The size of a gene or an organisms entire genome is often measured in base pairs because DNA is usually double-stranded. Hence, the number of base pairs is equal to the number of nucleotides in one of the strands. The haploid human genome is estimated to be about 3.2 billion bases long and to contain 20, a kilobase is a unit of measurement in molecular biology equal to 1000 base pairs of DNA or RNA. The total amount of related DNA base pairs on Earth is estimated at 5.0 x 1037, in comparison, the total mass of the biosphere has been estimated to be as much as 4 TtC. Hydrogen bonding is the interaction that underlies the base-pairing rules described above. Appropriate geometrical correspondence of hydrogen donors and acceptors allows only the right pairs to form stably. Purine-pyrimidine base pairing of AT or GC or UA results in proper duplex structure, the only other purine-pyrimidine pairings would be AC and GT and UG, these pairings are mismatches because the patterns of hydrogen donors and acceptors do not correspond. The GU pairing, with two bonds, does occur fairly often in RNA. Higher GC content results in higher melting temperatures, it is, therefore, on the converse, regions of a genome that need to separate frequently — for example, the promoter regions for often-transcribed genes — are comparatively GC-poor. GC content and melting temperature must also be taken into account when designing primers for PCR reactions, the following DNA sequences illustrate pair double-stranded patterns. By convention, the top strand is written from the 5 end to the 3 end, thus and this is due to their isosteric chemistry. One common mutagenic base analog is 5-bromouracil, which resembles thymine, most intercalators are large polyaromatic compounds and are known or suspected carcinogens. Examples include ethidium bromide and acridine, an unnatural base pair is a designed subunit of DNA which is created in a laboratory and does not occur in nature
. PMID 25725067.
