Refimprove date December 2009 Overdominance is a condition in genetics where the phenotype of the Zygosity heterozygote lies outside of the phenotypical range of both Zygosity homozygote parents. Overdominance can also be described as heterozygote advantage , wherein heterozygous individuals have a higher fitness than homozygous individuals. An example in humans is sickle cell anemia . This condition is determined by a single polymorphism biology polymorphism . Possessors of the deleterious allele have lower life expectancy, with Zygosity homozygotes rarely reaching 50 years of age. However, this allele also yields some resistance to malaria . Thus in regions where malaria exerts or has exerted a strong selective pressure, sickle cell anemia has been selected for its conferred partial resistance to the disease. While Zygosity homozygotes will have either no protection from malaria or a dramatic propensity to sickle cell anemia , Zygosity heterozygotes enjoy a partial resistance to both. citation needed date May 2011 The Gillespie Model Population Geneticist John H. Gillespie established the following model ref Gillespie 2004 ref class wikitable Genotype A sub 1 sub A sub 1 sub A sub 1 sub A sub 2 sub A sub 2 sub A sub 2 sub Relative fitness 1 1 hs 1 s Where h is the heterozygote effect and s is the recessive allele effect. Thus given a value for s i.e. 0 s 1 , h can yield the following information class wikitable h 0 A sub 1 sub dominant, A sub 2 sub recessive h 1 A sub 2 sub dominant, A sub 1 sub recessive 0 h 1 incomplete dominance h 0 overdominance h 1 Underdominance For the case of sickle cell anemia the situation corresponds to the case h 0 in the Gillespie Model . See also Polar overdominance Underdominance Notes Reflist 1 References cite book last Gillespie first John authorlink John H. Gillespie title Population Genetics A Concise Guide, Second Edition publisher Johns Hopkins University Press year 2004 isbn 0 8018 8008 4 Category Genetics Genetics stub es Sobredominancia ... more details
Refimprove date September 2007 Polar overdominance is a unique form of inheritance described in sheep whereby a mutation mutant Callipyge allele must be inherited from the father to cause muscle Organ hypertrophy hypertrophy big buttocks . See also Imprinting genetics MEG3 a gene occasionally expressed through polar overdominance External links cite journal doi 10.1126 science.273.5272.236 title Polar Overdominance at the Ovine callipyge Locus year 1996 last1 Cockett first1 Noelle E. last2 Jackson first2 Sam P. last3 Shay first3 Tracy L. last4 Farnir first4 Fr d ric last5 Berghmans first5 St phane last6 Snowder first6 Gary D. last7 Nielsen first7 Dahlia M. last8 Georges first8 Michel journal Science volume 273 issue 5272 pages 236 8 pmid 8662506 Category Genetics genetics stub ... more details
merge to Heterosis date October 2011 Dominance versus overdominance is a scientific controversy in the field of genetics that has persisted for more than a century. ref Birchler, J.A. Auger, D.L. Riddle, N.C. 2003 . In search of the molecular basis of heterosis. The Plant Cell . 15 2236 2239. ref These two alternative hypotheses were first stated in 1908. Genetic basis of heterosis When a population is small or inbred, it tends to lose genetic diversity. Inbreeding depression is the loss of fitness due to loss of genetic diversity. Inbred strains tend to be homozygous for recessive alleles that are mildly harmful or produce a trait that is undesirable from the standpoint of the breeder . Heterosis or hybrid vigor, on the other hand, is the tendency of outbred strains to exceed both inbred parents in fitness. Selective breeding of plants and animals, including hybridization, began long before there was an understanding of underlying scientific principles. In the early 20th century, after ... parent. Overdominance hypothesis . Scenario B . Over expression of certain genes in the heterozygous ... volume 28 pages 455 doi 10.1126 science.28.718.454 b pmid 17771943 issue 718 ref Overdominance ... advantage advantageous in the heterozygote . The overdominance hypothesis attributes to heterozygote .... The overdominance hypothesis was developed independently by Edward M. East 1908 ref cite journal ... of a field of maize pages 296 301 ref Dominance and overdominance have different consequences ... Crow , who in his younger days believed that overdominance was a major contributor to hybrid vigor ... for the overdominance theory among scientists studying plant hybridization. But overdominance implies ... to explain the superior yield of hybrids. Only a few conclusive cases of overdominance have been reported ... for contributions from overdominance and epistasis . But whether the best hybrids are getting an extra boost from overdominance or favorable epistatic contributions remains an open question. ref ... more details
Unreferenced auto yes date December 2009 In genetics , underdominance is the opposite of overdominance . It is the selection against the mean of a population distribution, causing disruptive selection and divergent genotype s. Underdominance can also be described as homozygote advantage , wherein homozygous individuals have a higher fitness than heterozygous individuals. See also Natural selection Heterozygote advantage Category Genetics Genetics stub ... more details
Dominance versus overdominance . In applied genetics selective and agricultural breeding , this controversy has reflected the century long debate over whether dominance or overdominance provides ..., then the prevalence of the classic Tay Sachs disease mutation in Ashkenazi Jews is a case of overdominance ... as evidence for overdominance, for the balancing hypothesis, and for selectionism in general. The classic ... Nicholas Wade ref Researchers of the 1960s and 1970s often favored theories of overdominance as an explanation ... in genetics. Among current researchers in medical genetics, interest in dominance versus overdominanceoverdominance as an explanation for heterozygote advantage has waned. Overdominance in particular ... ref In another review article, Crow notes that dominance versus overdominance dominance has become ... more details
Polar may refer to TOCRight Science, technology, and mathematics Polar satellite , a satellite launched by NASA in 1996 Polar cataclysmic variable , a strongly magnetic cataclysmic variable star system POLAR III and POLAR II, a pedestrian test dummy created by Honda, used to study pedestrian injuries in road traffic accidents Polar curve aviation , a diagram that depicts the gliding performance of an aircraft Polar fleece , an insulating synthetic wool fabric Polar overdominance a form of genetic mutation Chemical polarity , a concept in chemistry which describes how equally bonding electrons are shared between atoms Mathematics Pole and polar a point and a line , a construction in geometry Polar curve a point and a curve , a generalization of a point and a line Polar coordinate system , uses a central point and angles Polar set , with respect to a bilinear pairing of vector spaces Polar cone Television, film, and music Polar album Polar album , second album by the High Water Marks Polar artist , Norwegian electronic music artist Polar Studios , music studio of ABBA in Sweden Geography Pertaining to the Geographical pole , either of two fixed points on the surface of a spinning body or plant, at 90 degrees from the equator, based on the axis around which a body spins Pertaining to the Polar region , region within the polar circles, referred to as the Arctic and Antarctic Places Polar, Wisconsin , town in Langlade County, Wisconsin, United States Polar community , Wisconsin , unincorporated community in Langlade County, Wisconsin, United States Companies Polar Electro , a manufacturer of heart rate monitors Polar Air Cargo , an American airline Polar Airlines , a Russian airline See also intitle Polar Pole disambiguation Polarity disambiguation Polarization disambiguation disambig ca Polar cs Pol rn de Polar es Polar fr Polar ko nl Polar no Polar nn Polar pl Polar pt Polar desambigua o fi Polar ... more details
Merge Transgressive phenotype date November 2009 In genetics , transgressive segregation is the formation of extreme phenotype s, or transgressive phenotypes , observed in segregated Hybrid biology hybrid populations compared to phenotypes observed in the parental lines. ref name Nolte2005 ref name Rieseberg1999 Hybrid offspring generally possess traits or characteristics seen in ancestral species. These traits might be expected to be subdued or diluted when compared to the original species. Transgressive segregation attempts to explain situations when the converse is true, hybrid offspring that appear to have overstated traits when compared to the parental line. Transgressive segregation may be a major source of novel adaptation s in hybrids. ref name Rieseberg1999 There are many causes of transgressive segregation in hybrids such as recombination of Additive genetic effects additive alleles , an elevated mutation rate, reduced developmental stability, epistasis epistatic effects between allele s, or overdominance caused by heterozygosity at specific loci or chromosome number variation. ref name Rieseberg1999 Notes reflist refs ref name Rieseberg1999 cite journal title Transgressive segregation, adaptation and speciation journal Heredity date 1999 07 first Loren H. last Rieseberg pmid 10583537 coauthors Margaret A. Archer and Robert K. Wayne volume 83 pages 363 372 doi 10.1038 sj.hdy.6886170 accessdate 2010 11 17 issue 4 ref ref name Nolte2005 cite journal title Shape based assignment tests suggest transgressive phenotypes in natural sculpin hybrids Teleostei, Scorpaeniformes, Cottidae journal Frontiers in Zoology date 2005 06 29 first Arne W. last Nolte pmid 15987531 coauthors H David Sheets volume 2 pmc 1198242 pages 11 doi 10.1186 1742 9994 2 11 accessdate 2010 11 17 ref genarch Category Genetics Category Biological evolution evolution stub ... more details
The infinite alleles model is a mathematical model for calculating genetic mutation s. The Japanese geneticist Motoo Kimura and American geneticist James F. Crow 1964 introduced the infinite allele s model , an attempt to determine for a finite Ploidy Diploid diploid population what proportion of Locus genetics loci would be homozygous . This was, in part, motivated by assertions by other geneticists that more than 50 percent of Drosophila melanogaster Drosophila loci were heterozygous , a claim they initially doubted. In order to answer this question they assumed first, that there were a large enough number of alleles so that any mutation would lead to a different allele that is the probability of back mutation to the original allele would be low enough to be negligible and second, that the mutations would result in a number of different outcomes from neutral to Wiktionary deleterious deleterious . They determined that in the neutral case, the probability that an individual would be homozygous, F , was math F 1 over 4 N e u 1 math where u is the mutation rate, and N sub e sub is the effective population size . The effective number of alleles n maintained in a population is defined as the inverse of the homozygosity, that is math n 1 over F 4N e u 1 math which is a lower bound for the actual number of alleles in the population. If the effective population is large, then a large number of alleles can be maintained. However, this result only holds for the neutral case, and is not necessarily true for the case when some alleles are subject to selection , i.e. more or less fitness biology fit than others, for example when the fittest genotype is a heterozygote a situation often referred to as overdominance or heterosis . In the case of overdominance, because Mendelian inheritance Mendel s second law the law of segregation necessarily results in the production of homozygotes which are by definition in this case, less fit , this means that population will always harbor a ... more details
results, is outbreeding depression . Genetic basis of heterosis Main Dominance versus overdominance ... purely homozygous deleterious alleles at many loci. The overdominance hypothesis states that some ... advantage overdominance is not restricted to hybrid lineages. This hypothesis is commonly invoked ... more details
deals with the specific case of fitness overdominance , where the fitness advantage of the cross ... polymorphism Hybrid vigour Overdominance Polymorphism biology DEFAULTSORT Heterozygote Advantage Category ... more details
Infobox Horse name Warlander image Warlander Andalusian Friesian Cross .jpg image caption Warlander horse features Powerful build ref name Def cite web title Definition der Pferderasse Warlander Definition of the racehorse Warlander publisher Warlander Aus Franken url http www.warlander franken.de der warlander accessdate August 14, 2011 ref altname Destrier, Andalusian Friesian nickname country group1 BZKS std1 http www.spezialpferderassen.de component content article 51 rassebeschreibungen 187 zuchtziele des warlanders.html group2 ANCCE Andalusian progenitor std2 http www.ancce.es group3 FPS Frieisian progenitor std3 http www.kfps.nl The Warlander is a horse of baroque horse Baroque type , produced by crossing Andalusian horse Andalusian and Friesian horse Friesian breeds. The ideal Warlander combines the Andalusian s intelligence, facility for collection, flexibility, and powerful hindquarters, with the Friesian s tractability, dramatic leg action, bone , and strong forequarters. ref name Def History The crossing of Andalusian and Friesian horses to produce improved cavalry horses has a history going back to at least the sixteenth century, ref cite book author Sylvia Loch title The Royal Horse of Europe The Story of the Andalusian and Lusitano publisher J. A. Allen year 1986 isbn 0 85131 422 8 ref though the term Warlander was coined only in the late twentieth century to reflect both the breed registry s claim that this cross was historically used as a Horses in warfare war horse and its origins from two very old equine horse breeds . ref name CSS cite web title Warlander History The birth of the Warlander breed publisher Classical Sporthorse Stud Warlander breeders Australia url http www.warlander.com.au warlanderhistory.htm accessdate August 16, 2011 ref Characteristics Warlander breeders seek to augment the strongest and most desirable qualities of the Andalusian and Friesian breeds through the Dominance versus overdominance genetic heterosis created by combin ... more details
increase the level of homozygosity. Bruce Wallace , working with J. C. King , used the overdominance hypothesis to develop the balance position , which left a larger place for overdominance ... induced radiation may in fact facilitate an increase in fitness due to overdominance. This was also ... entail, though critics argued that the findings actually fit well with overdominance hypothesis. ref ... more details
Inbreeding depression is the reduced fitness biology fitness in a given population as a result of breeding of related individuals. It is often the result of a population bottleneck . In general, the higher the genetic variation within a breeding population, the less likely it is to suffer from inbreeding depression. Inbreeding depression seems to be present in most groups of organisms, but is perhaps most important in hermaphroditic species. The majority of plant s are hermaphroditic and thus are capable of the most severe degree of inbreeding depression. Mechanisms Image Shetland pony inbred.jpg thumb 350px right Example of inbreeding depression Breeding between closely related individuals, called inbreeding , may on one hand result in more recessive deleterious traits manifesting themselves, because the genome s of pair mates are more similar recessive traits can only occur in offspring if present in both parents genomes, and the more genetically similar the parents are, the more often recessive traits appear in their offspring. Consequently, the more closely related the breeding pair is, the more homozygous deleterious gene s the offspring may have, resulting in very unfit individuals. For allele s that confer an advantage in the heterozygous and or homozygous dominant state, the fitness of the homozygous recessive state may even be zero meaning sterility physiology sterile or unviable offspring . An example of inbreeding depression is shown to the right. In this case, a is a recessive allele which has negative effects. In order for the a phenotype to become active, the gene must end up as aa because in the gene A a , the A takes dominance over the a and the a does not have any effect. Due to evolutionary causes, recessive genes are, more often than not, detrimental phenotypes by causing the organism to be less fit to its natural environment. Another mechanism responsible for inbreeding depression is overdominance of heterozygous alleles. This can lead to reduced ... more details
among researchers has reflected three debates among geneticists at large Dominance versus overdominance ... long debate over whether dominance or overdominance provides the best explanation for heterosis ... more details
Use American English date July 2011 Other uses Natural Selection disambiguation Evolutionary biology Natural selection is the gradual, non random , process by which trait biology biological traits become either more or less common in a population as a function of differential reproduction of their bearers. It is a key mechanism of evolution . Variation exists within all populations of organisms. This occurs partly because random mutations cause changes in the genome of an individual organism, and these mutations can be passed to offspring. Throughout the individuals lives, their genomes interact with their environments to cause variations in traits. The environment of a genome includes the molecular biology in the cell, other cells, other individuals, populations, species, as well as the abiotic environment. Individuals with certain variants of the trait may survive and reproduce more than individuals with other variants. Therefore the population evolves. Factors that affect reproductive success are also important, an issue that Charles Darwin developed in his ideas on sexual selection , for example. Natural selection acts on the phenotype , or the observable characteristics of an organism, but the Genetics genetic heritable basis of any phenotype that gives a reproductive advantage will become more common in a population see allele frequency . Over time, this process can result in populations that specialize for particular ecological niche s and may eventually result in the speciation emergence of new species . In other words, natural selection is an important process though not the only process by which evolution takes place within a population of organisms. As opposed to artificial selection , in which humans favour specific traits, in natural selection the environment acts as a sieve through which only certain variations can pass. Natural selection is one of the cornerstones of modern biology . The term was introduced by Darwin in his influential 1859 book On th ... more details
About the disease itself the genetic transmission of sickle cell disease and its carrier state sickle cell trait Use British English date November 2010 Infobox disease Name Sickle cell disease Image Sickle cell 01.jpg Caption Figure A shows normal red blood cells flowing freely through veins. The inset shows a cross section of a normal red blood cell with normal hemoglobin. Figure B shows abnormal, sickled red blood cells log jamming, sticking and accumulating at the branching point in a vein. The inset image shows a cross section of a sickle cell with long polymerized HbS strands stretching and distorting the cell shape. DiseasesDB 12069 ICD10 ICD10 D 57 d 55 ICD9 ICD9 282.6 OMIM 603903 MedlinePlus 000527 eMedicineSubj med eMedicineTopic 2126 eMedicine mult eMedicine2 oph 490 eMedicine2 ped 2096 eMedicine2 emerg 26 eMedicine2 emerg 406 MeshName Sickle Cell anemia MeshNumber C15.378.071.141.150.150 GeneReviewsID sickle GeneReviewsName Sickle cell disease Sickle cell disease SCD , or sickle cell anaemia or anemia , SCA or drepanocytosis , is an autosome autosomal Autosomal recessive recessive genetic blood disorder with overdominance , characterized by red blood cell s that assume an abnormal, rigid, sickle shape. Sickling decreases the cells flexibility and results in a risk of various complications. The sickling occurs because of a mutation in the hemoglobin gene . Life expectancy is shortened. In 1994, in the US, the average life expectancy of persons with this condition was estimated to be 42 years in males and 48 years in females, ref cite journal author Platt OS, Brambilla DJ, Rosse WF, et al. title Mortality in sickle cell disease. Life expectancy and risk factors for early death journal N. Engl. J. Med. volume 330 issue 23 pages 1639 44 year 1994 month June pmid 7993409 url http content.nejm.org cgi content full 330 23 1639 doi 10.1056 NEJM199406093302303 issn 0028 4793 ref but today, thanks to better management of the disease, patients can live into their 50 ... more details
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