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Structural Variant
Genomic structural variation is the variation in structure of an organism's chromosome, such as deletions, duplications, Copy-number variation, copy-number variants, insertions, Chromosomal inversion, inversions and Chromosomal translocation, translocations. Originally, a structure variation affects a sequence length about 1kb to 3Mb, which is larger than SNPs and smaller than chromosome abnormality (though the definitions have some overlap). However, the operational range of structural variants has widened to include events > 50bp. Some structural variants are associated with genetic diseases, however most are not. Approximately 13% of the human genome is defined as structurally variant in the normal population, and there are at least 240 genes that exist as homozygous deletion polymorphism (biology), polymorphisms in human populations, suggesting these genes are dispensable in humans. While humans carry a median of 3.6 Mbp in SNPs (compared to a reference genome), a median of 8 ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Chromosome
A chromosome is a package of DNA containing part or all of the genetic material of an organism. In most chromosomes, the very long thin DNA fibers are coated with nucleosome-forming packaging proteins; in eukaryotic cells, the most important of these proteins are the histones. Aided by chaperone proteins, the histones bind to and condense the DNA molecule to maintain its integrity. These eukaryotic chromosomes display a complex three-dimensional structure that has a significant role in transcriptional regulation. Normally, chromosomes are visible under a light microscope only during the metaphase of cell division, where all chromosomes are aligned in the center of the cell in their condensed form. Before this stage occurs, each chromosome is duplicated ( S phase), and the two copies are joined by a centromere—resulting in either an X-shaped structure if the centromere is located equatorially, or a two-armed structure if the centromere is located distally; the jo ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Kilobase
A base pair (bp) is a fundamental unit of double-stranded nucleic acids consisting of two nucleobases bound to each other by hydrogen bonds. They form the building blocks of the DNA double helix and contribute to the folded structure of both DNA and RNA. Dictated by specific hydrogen bonding patterns, "Watson–Crick" (or "Watson–Crick–Franklin") base pairs (guanine–cytosine and adenine– thymine) allow the DNA helix to maintain a regular helical structure that is subtly dependent on its nucleotide sequence. The complementary nature of this based-paired structure provides a redundant copy of the genetic information encoded within each strand of DNA. The regular structure and data redundancy provided by the DNA double helix make DNA well suited to the storage of genetic information, while base-pairing between DNA and incoming nucleotides provides the mechanism through which DNA polymerase replicates DNA and RNA polymerase transcribes DNA into RNA. Many DNA-binding protein ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Haemophilia A
Haemophilia A (or hemophilia A) is a blood clotting disorder caused by a genetic deficiency in clotting factor VIII, thereby resulting in significant susceptibility to bleeding, both internally and externally. This condition occurs almost exclusively in males born to carrier mothers due to X-linked recessive inheritance. Nevertheless, rare isolated cases do emerge from de novo (spontaneous) mutations. The medical management of individuals with hemophilia A frequently entails the administration of factor VIII medication through slow intravenous injection. This intervention aims to address and preempt additional bleeding episodes in affected individuals. Signs and symptoms Haemophilia A's phenotype has a quite wide range of symptoms encompassing both internal and external bleeding episodes. Individuals with more severe haemophilia tend to experience more intense and frequent bleeding, whereas those with mild haemophilia typically exhibit milder symptoms unless subjected to sur ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Short Interspersed Element
Retrotransposons (also called Class I transposable elements) are mobile elements which move in the host genome by converting their transcribed RNA into DNA through reverse transcription. Thus, they differ from Class II transposable elements, or DNA transposons, in utilizing an RNA intermediate for the transposition and leaving the transposition donor site unchanged. Through reverse transcription, retrotransposons amplify themselves quickly to become abundant in eukaryotic genomes such as maize (49–78%) and humans (42%). They are only present in eukaryotes but share features with retroviruses such as HIV, for example, discontinuous reverse transcriptase-mediated extrachromosomal recombination. There are two main types of retrotransposons, long terminal repeats (LTRs) and non-long terminal repeats (non-LTRs). Retrotransposons are classified based on sequence and method of transposition. Most retrotransposons in the maize genome are LTR, whereas in humans they are mostly non-LTR. ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Unequal Crossing Over
Unequal crossing over is a type of gene duplication or deletion event that deletes a sequence in one strand and replaces it with a duplication from its sister chromatid in mitosis or from its homologous chromosome during meiosis. It is a type of chromosomal crossover between homologous sequences that are not paired precisely. Normally genes are responsible for occurrence of crossing over. It exchanges sequences of different links between chromosomes. Along with gene conversion, it is believed to be the main driver for the generation of gene duplications and is a source of mutation in the genome. Mechanisms During meiosis, the duplicated chromosomes (chromatids) in eukaryotic organisms are attached to each other in the centromere region and are thus paired. The maternal and paternal chromosomes then align alongside each other. During this time, recombination can take place via crossing over of sections of the paternal and maternal chromatids and leads to reciprocal recombination ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Single Nucleotide Polymorphism
In genetics and bioinformatics, a single-nucleotide polymorphism (SNP ; plural SNPs ) is a germline substitution of a single nucleotide at a specific position in the genome. Although certain definitions require the substitution to be present in a sufficiently large fraction of the population (e.g. 1% or more), many publications do not apply such a frequency threshold. For example, a G nucleotide present at a specific location in a reference genome may be replaced by an A in a minority of individuals. The two possible nucleotide variations of this SNP – G or A – are called alleles. SNPs can help explain differences in susceptibility to a wide range of diseases across a population. For example, a common SNP in the CFH gene is associated with increased risk of age-related macular degeneration. Differences in the severity of an illness or response to treatments may also be manifestations of genetic variations caused by SNPs. For example, two common SNPs in the ''A ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Gene Duplication
Gene duplication (or chromosomal duplication or gene amplification) is a major mechanism through which new genetic material is generated during molecular evolution. It can be defined as any duplication of a region of DNA that contains a gene. Gene duplications can arise as products of several types of errors in DNA replication and repair machinery as well as through fortuitous capture by selfish genetic elements. Common sources of gene duplications include ectopic recombination, retrotransposition event, aneuploidy, polyploidy, and replication slippage. Mechanisms of duplication Ectopic recombination Duplications arise from an event termed unequal crossing-over that occurs during meiosis between misaligned homologous chromosomes. The chance of it happening is a function of the degree of sharing of repetitive elements between two chromosomes. The products of this recombination are a duplication at the site of the exchange and a reciprocal deletion. Ectopic recombina ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Insertion (genetics)
In genetics, an insertion (also called an insertion mutation) is the addition of one or more nucleotide base pairs into a DNA sequence. This can often happen in Microsatellite (genetics), microsatellite regions due to the DNA polymerase slipping. Insertions can be anywhere in size from one base pair incorrectly inserted into a DNA sequence to a section of one chromosome inserted into another. The mechanism of the smallest single base insertion mutations is believed to be through base-pair separation between the template and primer strands followed by non-neighbor base stacking, which can occur locally within the DNA polymerase active site. On a chromosome level, an ''insertion'' refers to the insertion of a larger sequence into a chromosome. This can happen due to unequal Chromosomal crossover, crossover during meiosis. N region addition is the addition of non-coded nucleotides during genetic recombination, recombination by terminal deoxynucleotidyl transferase. P nucleotide ins ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Indel
Indel (insertion-deletion) is a molecular biology term for an insertion or deletion of bases in the genome of an organism. Indels ≥ 50 bases in length are classified as structural variants. In coding regions of the genome, unless the length of an indel is a multiple of 3, it will produce a frameshift mutation. For example, a common microindel which results in a frameshift causes Bloom syndrome in the Jewish or Japanese population. Indels can be contrasted with a point mutation. An indel inserts or deletes nucleotides from a sequence, while a point mutation is a form of substitution that ''replaces'' one of the nucleotides without changing the overall number in the DNA. Indels can also be contrasted with Tandem Base Mutations (TBM), which may result from fundamentally different mechanisms. A TBM is defined as a substitution at adjacent nucleotides (primarily substitutions at two adjacent nucleotides, but substitutions at three adjacent nucleotides have been observed). In ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Single-nucleotide Polymorphism
In genetics and bioinformatics, a single-nucleotide polymorphism (SNP ; plural SNPs ) is a germline substitution of a single nucleotide at a specific position in the genome. Although certain definitions require the substitution to be present in a sufficiently large fraction of the population (e.g. 1% or more), many publications do not apply such a frequency threshold. For example, a Guanine, G nucleotide present at a specific location in a reference genome may be replaced by an Adenine, A in a minority of individuals. The two possible nucleotide variations of this SNP – G or A – are called alleles. SNPs can help explain differences in susceptibility to a wide range of diseases across a population. For example, a common SNP in the Factor H, CFH gene is associated with increased risk of age-related macular degeneration. Differences in the severity of an illness or response to treatments may also be manifestations of genetic variations caused by SNPs. For example, two ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
