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Premutation
A premutation is a situation in which there are an excess number of repeats in a gene that is at risk of increasing in length during reproduction but which does not cause disease in the person with the excess number of repeats. Fragile X syndrome, a trinucleotide repeat disorder, is a condition in which premutations may be present in the parents of affected people. Huntington's disease is another example of a trinucleotide repeat disorder in which individuals with a certain excess of repeats (27–39) of the CAG codon in the Huntingtin Huntingtin (Htt) is the protein coded for in humans by the ''HTT'' gene, also known as the ''IT15'' ("interesting transcript 15") gene. Mutated ''HTT'' is the cause of Huntington's disease (HD), and has been investigated for this role and also for ... gene may not have the disease but are more likely to have a child with enough repeats (40+) to cause the disease.{{cite journal, vauthors=Walker FO, date=January 2007, title=Huntington's disease, journa ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Fragile X Syndrome
Fragile X syndrome (FXS) is a genetic disorder characterized by mild-to-moderate intellectual disability. The average IQ in males with FXS is under 55, while about two thirds of affected females are intellectually disabled. Physical features may include a long and narrow face, large ears, flexible fingers, and large testicles. About a third of those affected have features of autism such as problems with social interactions and delayed speech. Hyperactivity is common, and seizures occur in about 10%. Males are usually more affected than females. This disorder and finding of Fragile X syndrome has an X-linked dominant inheritance. It is typically caused by an expansion of the CGG triplet repeat within the ''FMR1'' (fragile X messenger ribonucleoprotein 1) gene on the X chromosome. This results in silencing ( methylation) of this part of the gene and a deficiency of the resultant protein (FMRP), which is required for the normal development of connections between neurons. Diagno ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Microsatellite
A microsatellite is a tract of repetitive DNA in which certain DNA motifs (ranging in length from one to six or more base pairs) are repeated, typically 5–50 times. Microsatellites occur at thousands of locations within an organism's genome. They have a higher mutation rate than other areas of DNA leading to high genetic diversity. Microsatellites are often referred to as short tandem repeats (STRs) by forensic geneticists and in genetic genealogy, or as simple sequence repeats (SSRs) by plant geneticists. Microsatellites and their longer cousins, the minisatellites, together are classified as VNTR (variable number of tandem repeats) DNA. The name "satellite" DNA refers to the early observation that centrifugation of genomic DNA in a test tube separates a prominent layer of bulk DNA from accompanying "satellite" layers of repetitive DNA. They are widely used for DNA profiling in cancer diagnosis, in kinship analysis (especially paternity testing) and in forensic identific ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Gene
In biology, the word gene (from , ; "...Wilhelm Johannsen coined the word gene to describe the Mendelian units of heredity..." meaning ''generation'' or ''birth'' or ''gender'') can have several different meanings. The Mendelian gene is a basic unit of heredity and the molecular gene is a sequence of nucleotides in DNA that is transcribed to produce a functional RNA. There are two types of molecular genes: protein-coding genes and noncoding genes. During gene expression, the DNA is first copied into RNA. The RNA can be directly functional or be the intermediate template for a protein that performs a function. The transmission of genes to an organism's 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 (many different genes) as well as gen ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Reproduction
Reproduction (or procreation or breeding) is the biological process by which new individual organisms – "offspring" – are produced from their "parent" or parents. Reproduction is a fundamental feature of all known life; each individual organism exists as the result of reproduction. There are two forms of reproduction: asexual and sexual. In asexual reproduction, an organism can reproduce without the involvement of another organism. Asexual reproduction is not limited to single-celled organisms. The cloning of an organism is a form of asexual reproduction. By asexual reproduction, an organism creates a genetically similar or identical copy of itself. The evolution of sexual reproduction is a major puzzle for biologists. The two-fold cost of sexual reproduction is that only 50% of organisms reproduce and organisms only pass on 50% of their genes.John Maynard Smith ''The Evolution of Sex'' 1978. Sexual reproduction typically requires the sexual interaction of two specializ ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Trinucleotide Repeat Disorder
Trinucleotide repeat disorders, also known as microsatellite expansion diseases, are a set of over 50 genetic disorders caused by trinucleotide repeat expansion, a kind of mutation in which repeats of three nucleotides ( trinucleotide repeats) increase in copy numbers until they cross a threshold above which they become unstable. Depending on its location, the unstable trinucleotide repeat may cause defects in a protein encoded by a gene; change the regulation of gene expression; produce a toxic RNA, or lead to chromosome instability. In general, the larger the expansion the faster the onset of disease, and the more severe the disease becomes. Trinucleotide repeats are a subset of a larger class of unstable microsatellite repeats that occur throughout all genomes. The first trinucleotide repeat disease to be identified was fragile X syndrome, which has since been mapped to the long arm of the X chromosome. Patients carry from 230 to 4000 CGG repeats in the gene that causes fr ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Huntington's Disease
Huntington's disease (HD), also known as Huntington's chorea, is a neurodegenerative disease that is mostly inherited. The earliest symptoms are often subtle problems with mood or mental abilities. A general lack of coordination and an unsteady gait often follow. It is also a basal ganglia disease causing a hyperkinetic movement disorder known as chorea. As the disease advances, uncoordinated, involuntary body movements of chorea become more apparent. Physical abilities gradually worsen until coordinated movement becomes difficult and the person is unable to talk. Mental abilities generally decline into dementia. The specific symptoms vary somewhat between people. Symptoms usually begin between 30 and 50 years of age but can start at any age. The disease may develop earlier in each successive generation. About eight percent of cases start before the age of 20 years, and are known as ''juvenile HD'', which typically present with the slow movement symptoms of Parkinson's d ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Codon
The genetic code is the set of rules used by living cells to translate information encoded within genetic material ( DNA or RNA sequences of nucleotide triplets, or codons) into proteins. Translation is accomplished by the ribosome, which links proteinogenic amino acids in an order specified by messenger RNA (mRNA), using transfer RNA (tRNA) molecules to carry amino acids and to read the mRNA three nucleotides at a time. The genetic code is highly similar among all organisms and can be expressed in a simple table with 64 entries. The codons specify which amino acid will be added next during protein biosynthesis. With some exceptions, a three-nucleotide codon in a nucleic acid sequence specifies a single amino acid. The vast majority of genes are encoded with a single scheme (see the RNA codon table). That scheme is often referred to as the canonical or standard genetic code, or simply ''the'' genetic code, though variant codes (such as in mitochondria) exist. History Efforts ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Huntingtin
Huntingtin (Htt) is the protein coded for in humans by the ''HTT'' gene, also known as the ''IT15'' ("interesting transcript 15") gene. Mutated ''HTT'' is the cause of Huntington's disease (HD), and has been investigated for this role and also for its involvement in long-term memory storage. It is variable in its structure, as the many polymorphisms of the gene can lead to variable numbers of glutamine residues present in the protein. In its wild-type (normal form), it contains 6-35 glutamine residues. However, in individuals affected by Huntington's disease (an autosomal dominant genetic disorder), it contains more than 36 glutamine residues (highest reported repeat length is about 250). Its commonly used name is derived from this disease; previously, the ''IT15'' label was commonly used. The mass of huntingtin protein is dependent largely on the number of glutamine residues it has; the predicted mass is around 350 kDa. Normal huntingtin is generally accepted to be 3144 am ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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