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In biology, a mutation is an alteration in the nucleic acid sequence of the genome of an organism, virus, or extrachromosomal DNA. Viral genomes contain either DNA or RNA. Mutations result from errors during DNA or viral replication, mitosis, or meiosis or other types of damage to DNA, which then may undergo error-prone repair, cause an error during other forms of repair, or cause an error during replication. Mutations may also result from substitution, insertion or deletion of segments of DNA due to mobile genetic elements.
A microsatellite is a tract of repetitive DNA in which certain DNA motifs 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.
Genetic recombination is the exchange of genetic material between different organisms which leads to production of offspring with combinations of traits that differ from those found in either parent. In eukaryotes, genetic recombination during meiosis can lead to a novel set of genetic information that can be further passed on from parents to offspring. Most recombination occurs naturally and can be classified into two types: (1) interchromosomal recombination, occurring through independent assortment of alleles whose loci are on different but homologous chromosomes ; & (2) intrachromosomal recombination, occurring through crossing over.
Molecular evolution describes how inherited DNA and/or RNA change over evolutionary time, and the consequences of this for proteins and other components of cells and organisms. Molecular evolution is the basis of phylogenetic approaches to describing the tree of life. Molecular evolution overlaps with population genetics, especially on shorter timescales. Topics in molecular evolution include the origins of new genes, the genetic nature of complex traits, the genetic basis of adaptation and speciation, the evolution of development, and patterns and processes underlying genomic changes during evolution.
Gene duplication 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.
In genetics and bioinformatics, a single-nucleotide polymorphism 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, many publications do not apply such a frequency threshold.
A germline mutation, or germinal mutation, is any detectable variation within germ cells. Mutations in these cells are the only mutations that can be passed on to offspring, when either a mutated sperm or oocyte come together to form a zygote. After this fertilization event occurs, germ cells divide rapidly to produce all of the cells in the body, causing this mutation to be present in every somatic and germline cell in the offspring; this is also known as a constitutional mutation. Germline mutation is distinct from somatic mutation.
In genetics, the mutation rate is the frequency of new mutations in a single gene, nucleotide sequence, or organism over time. Mutation rates are not constant and are not limited to a single type of mutation; there are many different types of mutations. Mutation rates are given for specific classes of mutations. Point mutations are a class of mutations which are changes to a single base. Missense, nonsense, and synonymous mutations are three subtypes of point mutations. The rate of these types of substitutions can be further subdivided into a mutation spectrum which describes the influence of the genetic context on the mutation rate.
Autism has multiple causes. This article focuses on heritable causes. The heritability of autism is the proportion of differences in expression of autism that can be explained by genetic variation; if the heritability of a condition is high, then the condition is considered to be primarily genetic. Autism has a strong genetic basis. Although the genetics of autism are complex, autism spectrum disorder (ASD) is explained more by multigene effects than by rare mutations with large effects.
Many causes of autism, including environmental and genetic factors, have been recognized or proposed, but understanding of the theory of causation of autism is incomplete. Attempts have been made to incorporate the known genetic and environmental causes into a comprehensive causative framework. ASD is a neurodevelopmental disorder marked by impairments in communicative ability and social interaction, as well as restricted and repetitive behaviors, interests, or activities not suitable for the individual's developmental stage. The severity of symptoms and functional impairment vary between individuals.
A postzygotic mutation is a change in an organism's genome that is acquired during its lifespan, instead of being inherited from its parent(s) through fusion of two haploid gametes. Mutations that occur after the zygote has formed can be caused by a variety of sources that fall under two classes: spontaneous mutations and induced mutations. How detrimental a mutation is to an organism is dependent on what the mutation is, where it occurred in the genome and when it occurred.
Enquiry into the evolution of ageing, or aging, aims to explain why a detrimental process such as ageing would evolve, and why there is so much variability in the lifespans of organisms. The classical theories of evolution suggest that environmental factors, such as predation, accidents, disease, and/or starvation, ensure that most organisms living in natural settings will not live until old age, and so there will be very little pressure to conserve genetic changes that increase longevity. Natural selection will instead strongly favor genes which ensure early maturation and rapid reproduction, and the selection for genetic traits which promote molecular and cellular self-maintenance will decline with age for most organisms.
Germline mosaicism, also called gonadal mosaicism, is a type of genetic mosaicism where more than one set of genetic information is found specifically within the gamete cells; conversely, somatic mosaicism is a type of genetic mosaicism found in somatic cells. Germline mosaicism can be present at the same time as somatic mosaicism or individually, depending on when the conditions occur. Pure germline mosaicism refers to mosaicism found exclusively in the gametes and not in any somatic cells. Germline mosaicism can be caused either by a mutation that occurs after conception, or by epigenetic regulation, alterations to DNA such as methylation that do not involve changes in the DNA coding sequence.
Exome sequencing, also known as whole exome sequencing (WES), is a genomic technique for sequencing all of the protein-coding regions of genes in a genome. It consists of two steps: the first step is to select only the subset of DNA that encodes proteins. These regions are known as exons—humans have about 180,000 exons, constituting about 1% of the human genome, or approximately 30 million base pairs. The second step is to sequence the exonic DNA using any high-throughput DNA sequencing technology.
Genomic structural variation is the variation in structure of an organism's chromosome, such as deletions, duplications, copy-number variants, insertions, inversions and translocations. Originally, a structure variation affects a sequence length about 1kb to 3Mb, which is larger than SNPs and smaller than chromosome abnormality. 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 polymorphisms in human populations, suggesting these genes are dispensable in humans. While humans carry a median of 3.6 Mbp in SNPs, a median of 8.9 Mbp is affected by structural variation which thus causes most genetic differences between humans in terms of raw sequence data.
Genome evolution is the process by which a genome changes in structure (sequence) or size over time. The study of genome evolution involves multiple fields such as structural analysis of the genome, the study of genomic parasites, gene and ancient genome duplications, polyploidy, and comparative genomics. Genome evolution is a constantly changing and evolving field due to the steadily growing number of sequenced genomes, both prokaryotic and eukaryotic, available to the scientific community and the public at large.
Philip Awadalla is a professor of medical and population genetics at the Ontario Institute for Cancer Research, and the Department of Molecular Genetics, Faculty of Medicine, University of Toronto. He is the National Scientific Director of the Canadian Partnership for Tomorrow's Health (CanPath), formerly the Canadian Partnership for Tomorrow Project (CPTP), and executive director of the Ontario Health Study. He is also the Executive Scientific Director of the Genome Canada Genome Technology Platform, the Canadian Data Integration Centre. Professor Awadalla was the Executive Scientific Director of the CARTaGENE biobank, a regional cohort member of the CPTP, from 2009 to 2015, and is currently a scientific advisor for this and other scientific and industry platforms. At the OICR, he is Director of Computational Biology.
ZTTK syndrome is a rare multisystem disease caused in humans by a genetic mutation of the SON gene. Common symptoms include developmental delay and often light to severe intellectual disability.
A somatic mutation is a change in the DNA sequence of a somatic cell of a multicellular organism with dedicated reproductive cells; that is, any mutation that occurs in a cell other than a gamete, germ cell, or gametocyte. Unlike germline mutations, which can be passed on to the descendants of an organism, somatic mutations are not usually transmitted to descendants. This distinction is blurred in plants, which lack a dedicated germline, and in those animals that can reproduce asexually through mechanisms such as budding, as in members of the cnidarian genus Hydra.
CHAMP1-associated intellectual disability syndrome, also known as autosomal dominant intellectual disability type 40, is a rare genetic disorder characterized by intellectual disabilities, developmental delays, facial dysmorphisms, and other anomalies.
References
- ↑ Veltman, Joris A.; Brunner, Han G. (2012). "De novo mutations in human genetic disease". Nature Reviews Genetics. 13 (8): 565–575. doi:10.1038/nrg3241. PMC 4110909 . PMID 22777127.
- ↑ Sanders, Stephan J.; Ercan-Sencicek, Gunes A.; Hus, Varun; Willsey, A. Jeremy; Murtha, Michael T.; Moreno-De-Luca, Daniela; Cho, Judy; Shi, Yunjia (2011). "Multiple recurrent de novo CNVs, including duplications of the 7q11.23 Williams syndrome region, are strongly associated with autism". Neuron. 70 (5): 863–885. doi:10.1016/j.neuron.2011.05.002. PMC 3939065 . PMID 21658581.
- ↑ Li, Jingjing; Oehlert, John; Snyder, Michael; Stevenson, David K.; Shaw, Gary M. (2017-04-07). "Fetal de novo mutations and preterm birth". PLOS Genetics. 13 (4): e1006689. doi: 10.1371/journal.pgen.1006689 . ISSN 1553-7390. PMC 5384656 . PMID 28388617.
- ↑ "Some parents pass on more mutations to their children than others". ScienceDaily. Retrieved 2022-06-05.
- ↑ Rahbari, R.; Wuster, A.; Lindsay, S.J.; Hurst, J.M.; Rahbari, R. (2016). "Timing, rates and spectra of human germline mutation". Nature Genetics. 48 (2): 126–133. doi:10.1038/ng.3469. PMC 4731925 . PMID 26656846.
- ↑ Bernkopf, Marie; Abdullah, Ummi B.; Bush, Stephen J.; Wood, Katherine A.; Ghaffari, Sahar; Giannoulatou, Eleni; Koelling, Nils; Maher, Geoffrey J.; Thibaut, Loïc M.; Williams, Jonathan; Blair, Edward M.; Kelly, Fiona Blanco; Bloss, Angela; Burkitt-Wright, Emma; Canham, Natalie (2023-02-15). "Personalized recurrence risk assessment following the birth of a child with a pathogenic de novo mutation". Nature Communications. 14 (1): 853. Bibcode:2023NatCo..14..853B. doi:10.1038/s41467-023-36606-w. ISSN 2041-1723. PMC 9932158 . PMID 36792598.
- ↑ Bernkopf, Marie; et al. (10 August 2023). "Personalized recurrence risk assessment following the birth of a child with a pathogenic de novo mutation". Nature Communications. 14 (1): 853. Bibcode:2023NatCo..14..853B. doi:10.1038/s41467-023-36606-w. PMC 9932158 . PMID 36792598.
- ↑ Hartl, Daniel L.; Clark, Andrew G. (2007). Principles of Population Genetics. Sinauer Associates. pp. 45–47. ISBN 978-0-87893-308-2.
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