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Genetics Terms
| A B C D E F G H I J K L M N O P Q R S T U V W X Y Z |
A
Activator: Activator is a DNA-binding protein, which is involved in gene expression. Activator increases the rate of transcription, usually by assisting in the formation of RNA polymerase.
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Alternative splicing: Alternative splicing is a variation in the process of splicing, in which the exons of the pre-messenger RNA are arranged in alternative ways. Pre-messenger RNA molecules that have been transcribed from the same gene are spliced and reconnected in different ways to create messenger RNAs (mRNAs).
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Alu repetitive sequence: Alu sequence, named so because it was first isolated in Anthrobacter luteus, is a short fragment of DNA found in human genome. It is the most abundant mobile sequence in human genome. Alu insertions lead to many hereditary diseases, including some forms of cancer.
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Antigenic variation: Antigenic variation is the process by which an infectious organism alters its surface proteins in order to evade a host immune response.
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Antisense Therapy: Antisense Therapy is a form of treatment for genetic disorders or infections. In this therapy, a specially synthesized stand of DNA or RNA binds to mRNA product of the disease-causing gene and inactivates it. Such an inactivation effectively stops the disease.
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Apoptosis: Apoptosis is a form of programmed cell death in multicellular organisms. It is one of the main types of programmed cell deaths and involves a series of biochemical events leading to a characteristic cell morphology and death.
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Autosome/Autosomal: Autosome is a non-sex chromosome. It is an ordinary paired chromosome that is the same in both genders of the species. Humans have 22 pairs of autosomes. A gene is referred to as an autosomal if it is located on one of the autosomal chromosomes. An attribute or a disorder is called autosomal if it is transmitted on one or more of the autosomal chromosomes. An autosomal attribute or disorder affects both the gendes equally.
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B
Bookmarking: Bookmarking in genetics, is a mechanism of epigenetic memory that allows the transmission of gene expression data in a cell to its daughter cells. It is thought that, at a point before mitosis, genes that exist in an expressed state are marked, thereby ensuring that daughter cells have the same pattern of gene expression as the cell from which they derived.
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C
Coactivator: Coactivator is a protein that increases the rate of gene expression by binding to an activator, which contains a DNA-binding domain. Coactivator also enhances transcription process by stabilizing the RNA polymerase.
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Codon: The gene sequence inscribed in DNA (and in RNA) is composed of tri-nucleotide units called codons, each coding for a single amino acid. Each nucleotide sub-unit consists of a phosphate, deoxyribose sugar and one of the 4 nitrogenous bases: Adenine, Guanine, Cytosine or Thymidine. (In RNA, Thymidine is substituted for Uracil.) Overall, there are 43 = 64 different codon combinations. For example, the RNA sequence UUUAAACCC contains the codons UUU, AAA and CCC, each of which specifies one amino acid. So, this RNA sequence represents a protein sequence, three amino acids long.
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Common founder effect: Common founder effect refers to the event when a new population is established by a small number of the individuals. The progeny of the common founder carries a limited number of the genetic variations found in the parent population. Certain alleles of the original population may be lost in the new population. As a result, the new population could be genotypically and phenotypically different from the original population.
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Cosmids: Cosmids are artificially created cloning vectors derived from a virus that infects phage lambda bacteria. Cosmids contain the cos gene of phage lambda. They are also referred to as plasmid vectors designed for cloning large fragments of eukaryotic DNA. They can accommodate about 40 kb of inserted DNA.
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D
De novo mutation: De novo mutation (new gene mutation) mutation is a mutation that appeared as a result of a mutation in a germ cell (egg or sperm) of one of the parents, or in the fertilized egg itself. It is a mutation which neither parent possessed or transmitted, and first appeared in the DNA of the affected individual.
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DNA hybridization: DNA hybridization is a technique by which the single strands of nucleic acids that are both complementary and from different sources can be mixed to form double-stranded molecules. The newly formed double-stranded DNA molecules are labeled as hybrid.
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DNA ligase: DNA ligase is an enzyme involved in the DNA synthesis and repair. Its function is to join the fragments of DNA together. DNA ligases are used in most laboratory DNA recombination techniques.
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DNA Microarrays: DNA Microarrays allow massive parallel gene expression and gene discovery studies. They are fabricated by high-speed robotics, generally on glass but sometimes on nylon substrates as well. An experiment with a single DNA chip can provide researchers information on thousands of genes simultaneously - a dramatic increase in throughput. DNA microarrays are used to determine the expression level of the genes, as well as to identify the gene sequence.
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DNA repair: DNA repair is a collection of processes by which cells correct the damage to their genetic material. Such damage can result from environmental insults or from errors that occur during the cell replication process. DNA repair is controlled by over 800 specialized proteins, function of which is encoded by the genes. Inability of the human cell to repair the damaged DNA may lead to diseases, such as cancer or diabetes.
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DNA replication/DNA synthesis: DNA replication/DNA synthesis is the process by which DNA is copied from the antiparallel strands. Each DNA strand can serve as a template for the complementary strand. The template strand is preserved as a whole piece and the new strand is assembled from nucleotide triphosphates. This type of replication is called semi-conservative replication.
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Dominant Allele: Alleles for an attribute always come in pairs. An allele is called dominant if it expresses itself even if it is heterozygous (does not have another same allele to match it). Dominant allele is written in capital letter, such as T for tallness. Some examples are: dark hair is dominant to blond hair, ability to taste is dominant to inability to taste, dimples are dominant to absence of dimples, tallness is dominant to short height in plants, etc.
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Downregulation: Downregulation is a process that decreases the rate of gene expression. Methylation of DNA is the most commonly occurring down regulating mechanism in eukaryotic cells.
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E
Exon arrays: Exon arrays is a molecular genetic technique that provides the most comprehensive analysis of gene expression. In this technique, multiples probes per exon enable exon-level analysis and allow to distinguish between different isoforms of the gene.
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G
Gene amplification : Gene amplification is a cellular process that is characterized by production of multiple copies of a particular& gene or genes. This process aims to enhance expression of the phenotype related to the amplified gene. Gene amplification is associated with many types of cancer, as well as with development of drug resistance.
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Gene silencing: Gene silencing refers to the normal process of switching off the gene, which would be otherwise active. Gene silencing is a normal process and is used to regulate endogenous genes. This process also appears to protect the genome from transposons and viruses.
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Gene therapy: Gene therapy is the insertion of genes into the human cells and tissues in order to treat disease and hereditary disease, in particular. The most common type of gene therapy is the replacement of the defective/mutant gene with the normal/healthy gene. A specific carrier molecules, called vector, is used to deliver the normal gene into the genome. Typically a modified virus is used as a vector.
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Genetic Pathway: A genetic pathway is the set of genes and the interactions occurring between them that collaborate to achieve a common function.
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Genotype: Genotype is a part of an individual's genome which contributes in determining a specific trait. Typically one refers to an individual's genotype with regard to a specific gene or trait of interest.
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Germline mutation: A germline mutation is any hereditary mutation that occurs in a germ cell. Germ cells are involved in reproduction of the organism. In humans, germ cells are eggs and spermatozoa. A mutation in a germ cell can be passed to the offspring. The sperm cells in the testes are much more likely to undergo a mutation than the cells in the ovaries, due to a high rate of cellular division of the spermatozoa.
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Glial cells: Glial cells, commonly called neuroglia or simply glia (Greek for "glue"), are non-neuronal cells that provide support and nutrition, maintain homeostasis, form myelin, and participate in signal transmission in the nervous system. In the human brain, glia are estimated to outnumber neurons by about 10 to 1.
Glial cells provide support and protection for neurons, the other main type of cell in the nervous system.
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H
Helicase: Helicase is a mobile enzyme which is involved in the process of DNA replication. It moves along the double-stranded DNA and separates the strands. Helicases are vital to all living organisms. Humans have 24 types of helicases, which catalyse a great variety of processes of strand separation.
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I
Insertion/Deletion mutation: A nucleotide may be added or removed from the DNA sequence. Such additions/removals often occur together and are collectively called indels. The addition or removal of one, two and more nucleotides can have devastating consequences to the gene, as it may cause a frame shift. The protein product of the gene is thus rendered dysfunctional. In addition, frame-shifting can create new stop codons and truncate the protein product of the gene. The insertion of three or multiples of three nucleotides may be less serious to the gene, as it does not change the reading frame of the gene. However, some serious diseases, like Huntington's chorea, are caused by insertion of many copies of the same triple nucleotide sequence.
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Intron: An intron, or an intragenic region is a section of DNA, that lies within a gene, but does not encode the protein that the gene produces. An intron is spliced out of the mRNA that is transcribed from the gene before translation.
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J
Junk DNA: Junk DNA is a collective term for DNA sequences, function of which have not been identified yet. Approximately 95% of the sequences in human genome have been designated as junk, including most sequences in the introns and intragenic sequences. Recent studies dispute the previously held notion of uselessness of the junk DNA and show that this part of the genome may be absolutely vital to the organisms' survival.
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L
Last common ancestor : Last common ancestor is a hypothetical last living organism from which all the other living organisms originated. It is also sometimes called last universal ancestor. This organism is thought to have lived 3.5 billion years ago.
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Lewis Carroll Problem: Lewis Carroll Problem in genetics is a combinatorial problem, wherein, given two sequences and a dictionary, the goal is to find the minimum number of substitutions to translate the first sequence into second, such that each of the intermediate sequences is in the specified dictionary.
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M
Micro RNA (miRNA): Micro RNA (miRNA) is a a single-stranded RNA molecule which is involved in regulation of gene expression. In a cell, miRNA is transcribed from DNA but is not further translated into protein, therefore it is often called non-coding RNA.
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Missense mutation: A missense mutation, also called non-synonymous mutation, is a type of point mutation where a nucleotide is changed, which results in the production of a different amino acid. Such mutations are responsible for diseases like Epidermolysis Bullosa and sickle cell disease. For example, in sickle cell disease, a codon GAG, which codes for amino acid glutamine, is changed to GTG, which codes for amino acid valine.
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Mitochondrial DNA (mtNDA): Mitochondrial DNA (mtNDA) is DNA that is contained within the mitochondria, one of the cellular organelles. In humans, mitochondrial DNA mappears to be 100% inherited from the mother, and maternal lineage can be traced back hundreds of generations based on studies of mtDNA. Unlike the DNA in the nucleus, which changes by 50% with each generation, there is very little change to the mitochondrial DNA. Thus, every mutation in mitochondria can be easily measured.
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Mitochondrial hereditary disease: Mitochondrial hereditary diseases are a group of disorders that arise from mutations in the mitochondrial DNA. Mitochondrial DNA inheritance differs from autosomal or sex-linked inheritance. Mitochondrial DNA is inherited from mother, and typically there are five to ten copies of DNA, which are then randomly assorted during cellular division.
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Monoclonal antibodies: Monoclonal antibodies are antibodies that are identical because they are all produced by one type of immune cells and are clones of a single parent cell. Monoclonal antibodies have become an important tool in medicine, biology and biochemistry.
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Morphological mutation: Morphological mutation is a type of mutation that results in changes of the outward appearance of the individual. Such characteristics like height, skin color or length of the limbs can be affected by morphological mutations, resulting in disorders such as achondroplasia or albinism.
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Mutation: Mutation in genetics or in biology refers to the changes in cellular DNA or RNA. Mutations may occur as result of endogenous processes, such as evolutionary pressure favoring the mutation, or they may occur under the influence of external factors, such as radiation, toxic chemicals and viral infections. Mutations are divided into germline mutations, which can be passed on to the progeny, and somatic mutations, which are not transmitted to the progeny.
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N
Nonsense mutation: Nonsense mutation is a type of a point mutation, which occurs in the protein-coding region of the gene. Nonsense mutation codes for a stop codon and results in a truncation of the protein.
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Nucleolus : Nucleolus is a cellular structure found within nucleus. Nucleolus consist of loops of DNA which are wrapped around histones. The function of nucleolus is to manufacture ribosomes.
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Nucleosome: Nucleosome is a fundamental packing unit of DNA. It consists of a short segment of DNA wrapped around a core histone protein. Nucleosomes are typically packed together inside the chromatin. This packing allows long strands of DNA to be compacted inside the cell nucleus.
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O
Open Reading Frame: An open reading frame or ORF is any sequence of DNA or RNA that can be translated into a protein. In a gene, ORFs are located between the start-code sequence (initiation codon) and the stop-code sequence (termination codon). ORFs are usually encountered when sifting through pieces of DNA while trying to locate a gene.
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P
Penetrance: Penetrance is a term used in genetics to describe the extent to which properties of a gene will be expressed. A highly& penetrant gene will express itself almost always, regardless of the effects of the environment, whereas gene with low penetrance will express the traits, for which it is coding, only under certain environmental conditions. It is possible to carry large number of low penetrance hereditary traits and never be aware of them.
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Pharmacogenetics: Pharmacogenetics refers to a study or clinical testing of how gene variations affect response to the drug. Pharmacogenetics is particularly concerned with adverse reactions to different drugs that often occur as a result of genetic variations in drug-metabolizing enzymes. Pharmacogenetics allows for better predictability of an individual's response to a particular drug.
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Phenome: Phenome is a set of all phenotypes represented in a cell, tissue, organ, organism or species. A phenome includes all the traits in an organism that are due to either genetic or environmental influences.
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Point mutation: Point mutation or substitution occurs when one base nucleotide is substituted for another in a DNA structure. Point mutation often also refers to the insertion or deletion of a single nucleotide in the DNA molecule. Point mutations may be spontaneous or hereditary. For example, sickle cell disease results from a hereditary point mutation.
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Polyclonal antibodies : Polyclonal antibodies are antibodies that are derived from different B-cell lines. They are a mixture of different immunoglobulin molecules that are secreted against a specific antigen. Each immunoglobulin molecule in the polyclonal antibody mix recognizes a specific binding site (epitope) on the antigen.
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Polymorphism: In biology/genetics, polymorphism means coexistence of several distinctly different genotypes in a population that lives in the same habitat. Examples include different blood groups in humans, different color forms in some butterflies, different size of snail shell. Polymorphism is considered a normal phenomenon, which contributes to the genotypic and phenotypic diversity. Some types of polymorphisms, such as hair and eye color allele polymorphism, affect the phenotype expression. Other types of polymorphism do not affect expression of the phenotype, and are often called neutral. Examples of neutral types of polymorphism include different responses of the members of the same population to drugs, viruses, bacteria or environmental toxins.
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Polysomy: Polysomy is a condition in which an organism has at least one more chromosome than normal, i.e. the number of a particular chromosome is not diploid - there may be three or more copies of the chromosome rather than the expected two copies. Polysomy is usually caused by non-disjunction (the failure of a pair of homologous chromosomes to separate) during meiosis, but may also be due to a translocation mutation. Down's syndrome is an example of polysomy where affected individuals possess three copies (trisomy) of chromosome 21.
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Purine: Purine is an aromatic compound which consists of two rings. Two of the bases in nucleic acid, adenine and guanine, are purines. In the nucleic acid molecule, purines form hydrogen bonds with complementary pyrimidine bases.
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Pyrimidine: Pyrimidine is an aromatic heterocyclic compound. In the DNA molecule, two bases are pyrimidines - thymine (T) and cytosine (C). In the RNA molecule, thymine is substituted for uracil (U). Pyrimidines form hydrogen bonds with the complementary purines: adenine pairs up with thymine in DNA (A-T), or with uracil in RNA (A-U). Guanine pairs up with cytosine (G-C).
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R
Recessive Allele:: An allele, which is not expressed in a heterozygous pair of alleles is called recessive. A recessive allele needs another matching allele (homozygous) in order to be expressed. A recessive allele is written in a small alphabet. Some examples of recessive conditions are: Cystic Fibrosis, Phenylketonuria, Hemochromatosis. Generally, diseases resulting from recessive inheritance are more severe than those resulting from dominant inheritance.
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Recombinant DNA technology: Recombinant DNA technology is used to produce artificial DNA sequences by combining two other DNA sequences in a plasmid. Recombinant proteins are produced by different genetically modified organisms by inserting the necessary DNA into their genome. Recombinant DNA technology is most widely used in pharmaceutical industry for production of hormones, such as insulin and growth hormone, as well as for production of synthetic blood clotting factors.
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Regulatory sequence: Regulatory sequence is a segment of DNA where the regulatory proteins, such as transcription factors bind preferentially. Regulatory sequences control gene expression and subsequently protein expression.
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Retrotransposons: Retrotransposons are small DNA elements that are present in all nucleated cells. Retrotransposons are able to transcribe themselves onto RNA and then back into DNA. Due to their rapid replication, retrotransposons are able to increase the size of a genome very fast. Approximately 42% of human genome consists of retrotransposons.
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RNA interference: RNA interference is a mechanism for RNA-guided regulation of gene expression in which double-stranded RNA molecules inhibit expression of the genes with complementary sequences. RNA interference was first though to have developed as form of innate immunity and protection against viruses. Now it is known that RNA interference also plays role in genome regulation and maintenance.
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S
Shotgun sequencing: Shotgun sequencing, also known as shotgun cloning, is a method used for sequencing long DNA strands. The method works by shredding the genome into smaller fragments of DNA which can be sequenced individually. The sequences of these fragments are then ordered, based on overlaps in the genetic code, and finally reassembled into the complete sequence.
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Single nucleotide polymorphism: A single nucleotide polymorphism (SNP) is a DNA sequence variation which occurs when a single nucleotide A, T, C or G differs between members of the same species. A genetic variation is considered an SNP when it occurs in 1% or more of the population. SNPs affect an individual's response to drugs, vaccines, pathogens and susceptibility to diseases.
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SiRNA (small interfering RNA): SiRNA (small interfering RNA), sometimes known as silencing RNA, is a short (20-25 nucleotide long), double stranded RNA, which is involved in gene expression. Due to its ability to silence virtually any gene, siRNA holds a strong potential for gene therapy.
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Start codon: Start codon is an ATG sequence of bases, which codes for an amino acid methionine. Start codon is universal for all living organisms. During the protein synthesis, start codon signals the beginning of a protein assembly.
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Stop codons: Stop codons are the triplets of amino acids that are encoded in every cell's DNA and are designated to stop the protein synthesis. There are three stop codons, UUA, UAG and UGA. It is not know why living cells have three stop codons and only one start codon, ATG.
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Synonymous codons: Synonymous codons are codons that all code for the same amino acid. As there are 64 codons and 20 amino acids, some codons code for the same amino acid. Such codons are referred to as synonymous codons. For example: UCU, UCC, UCA, and UCG all are synonymous codons that code for the amino acid Serine.
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Synonymous mutation: Synonymous mutation occurs when one nucleotide is substituted for another in a protein coding region of the gene, and such substitution does not alter the structure or function of the protein product. Such type of mutation is often called silent or neutral and is thought to have developed evolutionary to provide genetic diversity.
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T
Telomerase: Telomerase is an enzyme that is found in all eukaryotes. It adds specific DNA sequence repeats at the end of the chromosomes in the telomere region. This stabilizes the chromosomes and prevents the telomeres from shortening too fast during each replication cycle.
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Telomere: Telomere is a ribonucleoprotein complex composed of an RNA primer sequence and a protein component. Telomeres act to protect terminal ends of the chromosomes and to stabilize chromosomes during replication process. Telomeres prevent loss of vital genetic information from the ends of the chromosomes during each cell replication cycle.
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Transcription: Transcription is a process, in which genetic information is copied into RNA by an enzyme - RNA polymerase. Transcription has some proofreading mechanisms, but they are fewer and less effective than the controls for DNA, therefore, transcription has a lower copying fidelity than DNA replication.
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Transcription factor: Transcription factor is a small fragment of genetic material, which regulates expression of the genes and proteins that are encoded by those genes. Transcription factor contains DNA-binding domain which binds to the specific site on the regulated gene.
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Transfer RNA (tRNA): Transfer RNA (tRNA) is a small sequence of nucleotides, which attaches a specific amino acid to a forming chain of polypeptide at the ribosomal side of protein synthesis during translation.
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Transition: Transition is a change in the structure of a DNA molecule, when a purine nucleotide is substituted for a purine nucleotide (A for G or vise versa), or pyrimidine nucleotide is substituted for another pyrimidine nucleotide (T for C or vise versa).
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Translation: Translation is a process of protein biosynthesis and part of gene expression. Translation occurs in cytoplasm, where ribosomal subunits are located. During translation, genetic information from messenger RNA is decoded (translated) to produce the chain of amino acids, which are later joined together to form a protein. Translation has four steps: activation, initiation, elongation and termination.
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Transposons: Transposons are genes that move from one location to another on a chromosome. Due to such movement, transposons are commonly referred to as "jumping genes".
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Transversion: Transversion is a type of a change in the structure of the DNA molecule when a purine is substituted for a pyrimidine or vice versa. Transversion changes chemical structure of the DNA, therefore causing severe consequences for the cell. Transversion can be reverted by a spontaneous reversion only.
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Tumor suppressor gene: Tumor suppressor gene is a normal gene that confers protection against cancer by regulating cell division, repair of damaged DNA and apoptosis (programmed cell death). Several tumor suppressor genes have been identified, among them p53 and BRCA-1 and BRCA-2. Mutations that cause the inactivation of tumor suppressor genes are associated with cancer development. Such mutation can be both, hereditary or acquired.
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U
Universal Genetic Code: Universal Genetic Code, also known as the genetic code, is a set of rules that maps gene sequences to proteins in the living cell. It is a fundamental part of genome expression. Essentially, it dictates which one of the twenty possible amino acids will be produced by a particular tri-nucleotide section of gene sequence. For example, tri-nucleotide sequence UUU encodes for Phenylalanine amino acid, while tri-nucleotide sequences ACU and ACA encode for Threonine.
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Upregulation: Upregulation of a gene expression is a process by which a eukaryotic cell increases amount of a specific protein product. Such protein products may include receptors, enzymes, neurotransmitters and hormones. Upregulation generally occurs as a result of specific stimuli from the outside of the cell.
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X
X-linked dominant inheritance: X-linked dominant inheritance follows a similar pattern to autosomal dominant inheritance. But unlike autosomal dominant disorders, which affect both genders equally, X-linked dominant disorder affect males more than females. X-linked dominant disorders are very rare. Some examples include incontinentia pigmenti and Rett syndrome.
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X-linked recessive inheritance: X-linked recessive trait is commonly called sex-linked inheritance. It results from a mutation in the X-chromosome of the last pair of chromosomes, sex chromosomes. Since males have only one X-chromosome, which they inherit from their mother, they are by definition homozygous. Females become affected only if they inherit two mutated X chromosome - one from each parent.
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Y
Y-chromosome analysis: Y-chromosome analysis is a type of cytogenetic study that is used in genealogy to establish a relation between males. It is also used in wide-scale anthropologic studies to establish a relation between ethnic groups that could have originated from the same ancestors but were later spread over distant territories. Y chromosome typically contains very few coding genes and is passed from generation to generation virtually unchanged. In addition, the proof-reading of Y-chromosome before copying is exquisitely accurate, which does not allow much of the copying errors to be passed from generation to generation.
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