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Letteratura scientifica selezionata sul tema "Linkage disequilibrium"

Autore: Grafiati

Pubblicato: 4 giugno 2021

Ultima modifica: 6 luglio 2024

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Articoli di riviste sul tema "Linkage disequilibrium"

Tachida, Hidenori. "Decay of linkage disequilibrium in a finite island model". Genetical Research 64, n. 2 (ottobre 1994): 137–44. http://dx.doi.org/10.1017/s0016672300032742.

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SummaryTime-dependent behaviour of linkage disequilibrium when there was initial linkage disequilibrium is studied in a finite island model assuming neutrality. Explicit expressions for linkage disequilibrium parameters are obtained. From these expressions, the initial and the ultimate decay rates of linkage disequilibrium parameters are found to be increased and decreased, respectively, by finiteness of the population when recombination rate, migration rate and inverse of subpopulation size are of comparable order. Thus, linkage disequilibrium created in the past may persist longerin smaller subdivided populations. Also, differentiation of the gametic parameter of linkage disequilibrium among subpopulations is found to diminish quickly compared tothe linkage disequilibrium in the whole population. Implications of these results for the interpretation of linkage disequilibria in natural populations are discussed.

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Weitzman, Jonathan B. "Linkage disequilibrium". Genome Biology 2 (2001): spotlight—20010514–01. http://dx.doi.org/10.1186/gb-spotlight-20010514-01.

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Miyashita, Naohiko T., Montserrat Aguadé e Charles H. Langley. "Linkage disequilibrium in the white locus region of Drosophila melanogaster". Genetical Research 62, n. 2 (ottobre 1993): 101–9. http://dx.doi.org/10.1017/s0016672300031694.

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SummaryLinkage disequilibrium between molecular polymorphisms in a 10 kb region in the white locus of Drosophila melanogaster, revealed with a battery of four-cutter restriction enzymes, was investigated in 266 lines sampled from seven natural populations around the world. A total of 73 (35 restriction site, 37 insertion/deletion and 1 inversion) polymorphisms were detected, of which 55 non-unique polymorphisms were analysed for linkage disequilibrium. Clustering of significant linkage disequilibrium was observed in the transcriptional unit of the white locus as in Miyashita & Langley (1988). It was shown that about two thirds of the 2-locus combinations showing significant linkage disequilibrium have similar degree and direction of association over different populations. Despite lower divergence in allelic frequencies of molecular polymorphisms among populations, an increase in the proportion of 2-locus pairs showing significant linkage disequilibrium is observed in the transcriptional unit. Large values of Ohta's D measure ratio (1982 a, b) cluster in the transcriptional unit, and correspond to significant linkage disequilibria. Although the exact molecular mechanism is not clear, these results suggest that epistatic selection is responsible for significant linkage disequilibrium in the transcriptional unit of this locus

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Wu, Rongling, e Zhao-Bang Zeng. "Joint Linkage and Linkage Disequilibrium Mapping in Natural Populations". Genetics 157, n. 2 (1 febbraio 2001): 899–909. http://dx.doi.org/10.1093/genetics/157.2.899.

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Abstract A new strategy for studying the genome structure and organization of natural populations is proposed on the basis of a combined analysis of linkage and linkage disequilibrium using known polymorphic markers. This strategy exploits a random sample drawn from a panmictic natural population and the open-pollinated progeny of the sample. It is established on the principle of gene transmission from the parental to progeny generation during which the linkage between different markers is broken down due to meiotic recombination. The strategy has power to simultaneously capture the information about the linkage of the markers (as measured by recombination fraction) and the degree of their linkage disequilibrium created at a historic time. Simulation studies indicate that the statistical method implemented by the Fisher-scoring algorithm can provide accurate and precise estimates for the allele frequencies, recombination fractions, and linkage disequilibria between different markers. The strategy has great implications for constructing a dense linkage disequilibrium map that can facilitate the identification and positional cloning of the genes underlying both simple and complex traits.

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Kuno, Shin-ichi. "Division of linkage disequilibrium between absolute linkage disequilibrium and linkage equilibrium". Journal of Human Genetics 50, n. 6 (giugno 2005): 315–16. http://dx.doi.org/10.1007/s10038-005-0256-6.

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Baird, Stuart J. E. "Exploring linkage disequilibrium". Molecular Ecology Resources 15, n. 5 (11 agosto 2015): 1017–19. http://dx.doi.org/10.1111/1755-0998.12424.

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Schaeffer, S. W., e E. L. Miller. "Estimates of linkage disequilibrium and the recombination parameter determined from segregating nucleotide sites in the alcohol dehydrogenase region of Drosophila pseudoobscura." Genetics 135, n. 2 (1 ottobre 1993): 541–52. http://dx.doi.org/10.1093/genetics/135.2.541.

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Abstract The alcohol dehydrogenase (Adh) region of Drosophila pseudoobscura, which includes the two genes Adh and Adh-Dup, was used to examine the pattern and organization of linkage disequilibrium among pairs of segregating nucleotide sites. A collection of 99 strains from the geographic range of D. pseudoobscura were nucleotide-sequenced with polymerase chain reaction-mediated techniques. All pairs of the 359 polymorphic sites in the 3.5-kb Adh region were tested for significant linkage disequilibrium with Fisher's exact test. Of the 74,278 pairwise comparisons of segregating sites, 127 were in significant linkage disequilibrium at the 5% level. The distribution of five linkage disequilibrium estimators D(ij), D2, r(ij), r2 and D(ij) were compared to theoretical distributions. The observed distributions of D(ij), D2, r(ij) and r2 were consistent with the theoretical distribution given an infinite sites model. The observed distribution of D(ij) differed from the theoretical distribution because of an excess of values at -1 and 1. No spatial pattern was observed in the linkage disequilibrium pattern in the Adh region except for two clusters of sites nonrandomly associated in the adult intron and intron 2 of Adh. The magnitude of linkage disequilibrium decreases significantly as nucleotide distance increases, or a distance effect. Adh-Dup had a larger estimate of the recombination parameter, 4Nc, than Adh, where N is the effective population size and c is the recombination rate. A comparison of the mutation and recombination parameters shows that 7-17 recombination events occur for each mutation event. The heterogeneous estimates of the recombination parameter and the inverse relationship between linkage disequilibrium and nucleotide distance are no longer significant when the two clusters of Adh intron sites are excluded from analyses. The most likely explanation for the two clusters of linkage disequilibria is epistatic selection between sites in the cluster to maintain pre-mRNA secondary structure.

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Lou, Xiang-Yang, George Casella, Ramon C. Littell, Mark C. K. Yang, Julie A. Johnson e Rongling Wu. "A Haplotype-Based Algorithm for Multilocus Linkage Disequilibrium Mapping of Quantitative Trait Loci With Epistasis". Genetics 163, n. 4 (1 aprile 2003): 1533–48. http://dx.doi.org/10.1093/genetics/163.4.1533.

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AbstractFor tightly linked loci, cosegregation may lead to nonrandom associations between alleles in a population. Because of its evolutionary relationship with linkage, this phenomenon is called linkage disequilibrium. Today, linkage disequilibrium-based mapping has become a major focus of recent genome research into mapping complex traits. In this article, we present a new statistical method for mapping quantitative trait loci (QTL) of additive, dominant, and epistatic effects in equilibrium natural populations. Our method is based on haplotype analysis of multilocus linkage disequilibrium and exhibits two significant advantages over current disequilibrium mapping methods. First, we have derived closed-form solutions for estimating the marker-QTL haplotype frequencies within the maximum-likelihood framework implemented by the EM algorithm. The allele frequencies of putative QTL and their linkage disequilibria with the markers are estimated by solving a system of regular equations. This procedure has significantly improved the computational efficiency and the precision of parameter estimation. Second, our method can detect marker-QTL disequilibria of different orders and QTL epistatic interactions of various kinds on the basis of a multilocus analysis. This can not only enhance the precision of parameter estimation, but also make it possible to perform whole-genome association studies. We carried out extensive simulation studies to examine the robustness and statistical performance of our method. The application of the new method was validated using a case study from humans, in which we successfully detected significant QTL affecting human body heights. Finally, we discuss the implications of our method for genome projects and its extension to a broader circumstance. The computer program for the method proposed in this article is available at the webpage http://www.ifasstat.ufl.edu/genome/~LD.

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Hsu, Fang-Chi, Kung-Yee Liang e Terri H. Beaty. "Multipoint linkage disequilibrium mapping approach: Incorporating evidence of linkage and linkage disequilibrium from unlinked region". Genetic Epidemiology 25, n. 1 (11 giugno 2003): 1–13. http://dx.doi.org/10.1002/gepi.10241.

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Sabatti, Chiara, e Neil Risch. "Homozygosity and Linkage Disequilibrium". Genetics 160, n. 4 (1 aprile 2002): 1707–19. http://dx.doi.org/10.1093/genetics/160.4.1707.

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Abstract We illustrate how homozygosity of haplotypes can be used to measure the level of disequilibrium between two or more markers. An excess of either homozygosity or heterozygosity signals a departure from the gametic phase equilibrium: We describe the specific form of dependence that is associated with high (low) homozygosity and derive various linkage disequilibrium measures. They feature a clear biological interpretation, can be used to construct tests, and are standardized to allow comparison across loci and populations. They are particularly advantageous to measure linkage disequilibrium between highly polymorphic markers.

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Più fonti

Tesi sul tema "Linkage disequilibrium"

Hernandez-Sanchez, Jules. "Gene mapping using linkage disequilibrium". Thesis, University of Edinburgh, 2002. http://hdl.handle.net/1842/14058.

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The power of QTL detection was studied both empirically and deterministically for several methods. TDT was more powerful than a linkage test, but less powerful than a pure association test. There were no great differences in power between TDTs. One of the TDTs was implemented in BLUP (Best Linear Unbiased Prediction) to study the effect of a candidate gene, the melanocortin 4- receptor (MC4R), on growth, appetite and fatness in pigs. We found significant effects on growth and fatness but not on appetite. TDT uses within families genetic variation. A novel parameter to estimate gene effects using between families genetic variation was also included. If there is no spurious disequilibrium both estimates should be identical, otherwise only the within-families estimator is unbiased. It was more powerful to simulate missing parental genotypes with Gibbs Sampling than analysing data with sib-ship TDTs disregarding parental information. TDT was also used in a genome-wide search for markers associated with bovine spongiform encaphalopathy (BSE). TDT was implemented using logistic regressions, more amenable to statistical modelling than the original form. Maker loci near the Prion Protein gene did not show any associations with BSE, however, markers located on chromosomes 5, 10 and 20, did. A second study that focused on these three chromosomal regions confirmed the association for the marker on chromosome 5. TDT has shown reasonable power and exceptional robustness when mapping QTL in structured populations. Therefore TDT should be part of the gene cartographers’ continuously evolving arsenal of tools for gene mapping. However, previously published TDTs were developed for analysing human populations, whereas domestic/wild populations have different structures and histories that may require alternative statistical analyses. Linked gene flow (LGF) theory can be used for predicting identity-by-descent (IBD) probabilities between individuals. IBD probabilities are at the core of mixed model equations for mapping QTL in outbred populations via variance components estimation. In this thesis, LGF theory was used for determining inbreeding within each individual and chromosomal location using multi-marker information, hence paving the way for further developments.

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Veroneze, Renata. "Linkage disequilibrium and genomic selection in pigs". Universidade Federal de Viçosa, 2015. http://www.locus.ufv.br/handle/123456789/7597.

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A seleção genômica (SG) e associação genômica ampla (GWAS) são métodos que exploram o desequilíbrio de ligação (LD) entre marcadores e loci de características quantitativas (QTL). Um dos fatores limitantes para a implementação da SG é a necessidade de um grande número de animais genotipados e fenotipados para obtenção de valores genéticos com alta acurácia. Essa limitação pode ser superada combinando dados de múltiplas populações ou utilizando dados de animais cruzados. O objetivo geral desta tese foi caracterizar os padrões de LD de diferentes populações de suínos. Além disso, avaliar em que medida as diferenças de LD se refletem na acurácia da seleção genômica quando utilizadas diferentes metodologias e arranjos para população de referência e validação. Os arranjos testados foram: utilização de subconjuntos da mesma população como referência e validação (within), populações diferentes nos conjuntos de referência e validação (across) e combinação de duas populações na referência (multi). Nessa tese foram utilizados dados de suínos de linhas puras e de animais cruzados, genotipados com o PorcineSNP60 BeadChip. A regressão Loess proporcionou melhor ajuste aos dados de LD, bem como em predições mais acuradas em comparação a regressão não linear. Mostrou-se também, que a regressão Loess pode ser utilizada para realizar uma comparação estatística do LD decay de diferentes populações. A persistência de fase do LD entre animais cruzados e as linhas puras parentais foi alta, o que nos leva a hipotetizar que associações marcador-QTL similares poderiam ser encontradas em animais cruzados e as linhas parentais e, portanto, esperava-se encontrar altas acurácias de predição genômica entre essas populações. Entre as linhas puras a persistência de fase foi baixa, logo painéis de SNPs de maior densidade deveriam ser utilizados para manter a mesma associação marcador-QTL entre essas linhas. Acurácias obtidas na predição genômica utilizando animais cruzados assim como os arranjos across e multi, não seguiram as expectativas baseadas em LD. Portanto, a consistência de fase de ligação entre populações pode não ser tão importante para a acurácia da seleção genômica como se pensava, mas sim a ação combinada de LD, arquitetura genética e frequências alélicas. Portanto, foi desenvolvida uma metodologia que leva em consideração differenças nas frequências alélicas, bem como informações dos GWAS para comtemplar a arquitetura genética da característica. Esta estratégia trouxe alguns benefícios para a predição genônima para os arranjos within e multi. Ponderações obtidas por meio de GWAS em diferentes conjuntos de dados (uma única população e combinando múltiplas populações) nem sempre resultou em aumento da acurácia, sendo dependente da linha que estava sob seleção. O uso de pesos advindos do GWAS ao se utilizar uma população combinada resultou nas melhores acurácias tanto para os arranjos within quanto multi. A avaliação e o entendimento de como diferenças de LD, frequências alélicas e arquitetura genética afetam a acurácia da predição genômica é fundamental para otimizar a inserção da seleção genômica no melhoramento de suínos.
Genomic selection and genomic wide association studies (GWAS) are widely used methods that aim to exploit the linkage disequilibrium (LD) between markers and quantitative trait loci (QTL). Securing a sufficiently large set of genotypes and phenotypes can be a limiting factor when implementing genomic selection that may be overcome by combining data from multiple populations or using crossbred information. The overall objective of this thesis was to characterize LD patterns in different pig populations and to evaluate whether the differences in LD determine the accuracy of genomic predictions when using different reference sets (within-, across- and multi- population) and methodologies. In this thesis I used data from pure lines and crossbred pig populations genotyped with PorcineSNP60 BeadChip. Loess regression provided a better fit to the real LD data, and more accurate LD predictions could be made, compared to nonlinear regression. It was also shown that Loess regression can be used to statistically compare the LD decay of different populations. The persistence of LD phase between crosses and the parental pig lines was found to be high, from which it was hypothesized that similar marker-QTL associations would be found in a cross and in their purebred parent populations and therefore accuracies of genomic prediction across these populations should be high. Between the pure lines the persistence of phase was low, thus higher density panels should be used to have the same marker-QTL associations across these lines. Accuracies obtained from across- and multi-population genomic prediction and from using crossbred data did however not follow the expectations based on LD. Having the same LD phase may therefore not be as important for genomic prediction accuracy as previously thought but rather the interplay between LD, genetic architecture and allele frequencies also plays a major role. Differences in allele frequencies between lines and information from GWAS on the genetic architecture of traits for the different lines were taken into account in analyses developed in the later chapters. The use of weights, based on GWAS results, was expected to lead the GBLUP model towards the real genetic architecture of the traits. This strategy was shown to have some benefit for the genomic predictions with single- and multi-population data sets. Weights obtained from GWAS in different data sets (within and combining populations) did not always lead to increased accuracies of prediction, depending on which lines the weights are applied to. Using weights from GWAS in a combined population was the best approach, resulting in higher accuracy of GBLUP predictions within single- as well as in multi-population analysis. Understanding and evaluating how the accuracy of within-, across- and multi-population genomic prediction is affected by differences in LD, in genetic architecture and in allele frequencies is key to optimize the accuracy of genomic prediction in pig breeding.

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Liu-Cordero, Shau Neen 1970. "Patterns of linkage disequilibrium in the human genome". Thesis, Massachusetts Institute of Technology, 2002. http://hdl.handle.net/1721.1/89344.

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Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Biology, 2002.
Includes bibliographical references.
Although enormous progress has occurred in the field of human genetics, the cloning of complex trait mutations remains a challenging and unresolved process. This continuing difficulty is responsible for an ever-increasing awareness of the phenomenon of linkage disequilibrium (LD). The principle behind LD is relatively simple. Over the lifetime of a population, the genetic markers that are adjacent to an ancestral mutation will recombine less often than more distant markers. Therefore, the ancestral alleles of the markers closest to the mutation should be most frequent in a collection of disease chromosomes. The allelic association should decrease as the distance from the ancestral disease mutation increases. This thesis is a collection of ideas and experiments aimed at dissecting the behavior of LD in the human genome. Specific studies examine LD in a variety of populations including isolated founder populations, as well as globally diverse population samples. A large number of regions throughout the genome are investigated using both pairwise comparisons of markers, as well as multimarker haplotypes. The X chromosome is more closely scrutinized because of its unique population history, as well as the advantages afforded to haplotyping due to hemizygosity of the X chromosome in males. Major conclusions include the observation that LD between pairs of markers is highly variable even at extremely close distances and multimarker haplotypes better serve to resolve the underlying haplotype structure of the genome.
(cont.) The genome appears to be structured as blocks of limited haplotype diversity that do not exhibit much internal recombination but which are separated by segments that show little or no LD. The lack of LD between haplotype blocks appears to be due to clustering of recombination events into specific hotspots. The size of the blocks and haplotype diversity varies slightly by population. In addition, the identity of the haplotypes varies between populations. The existence of 3-4 major haplotypes for specific regions in a diverse human population sample is a surprising finding that was originally believed to have only existed in very special isolated and young populations.
by Shau Neen Liu-Cordero.
Ph.D.

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Li, Na. "Modeling and inference for linkage disequilibrium and recombination /". Thesis, Connect to this title online; UW restricted, 2003. http://hdl.handle.net/1773/9532.

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Cummings, James Rowland Fraser. "Linkage Disequilibrium Mapping of Chromosome 19 on Crohn's Disease". Thesis, University of Oxford, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.531666.

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Lawrence, Robert W. "Characterizing patterns of linkage disequilibrium in the human genome". Thesis, University of Oxford, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.496992.

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Holloway, J. Kim. "Linkage disequilibrium and meiotic recombination in the human genome". Thesis, University of Leicester, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.426035.

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Dale, Kuys Ruth. "Linkage disequilibrium in the South African abalone, Haliotis midae". Thesis, Stellenbosch : Stellenbosch University, 2015. http://hdl.handle.net/10019.1/97991.

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Thesis (MSc)--Stellenbosch University, 2015.
ENGLISH ABSTRACT: Linkage disequilibrium (LD) is defined as the non-random association of alleles at two or more loci within a population. It is sensitive to a variety of locus-specific- and demographic factors, and can thus provide much insight into the micro-evolutionary factors that have shaped species of interest. It can also be exploited to identify the genomic regions determining complex traits of interest, which can then be applied as performance evaluation markers in marker-assisted selection (MAS). The South African abalone, Haliotis midae, supports a rapidly developing aquaculture production industry, in which genetic improvement potential is high. This species also represents an opportunistic model for studying the effects of early domestication in a shellfish species. The aim of this study was therefore to quantify and characterise levels of genome-wide LD within the South African abalone, and to demonstrate its utility within population genetic investigations and the characterisation of complex traits. Estimates of LD between 112 mapped microsatellite markers within wild and cultured H. midae revealed that levels of LD in abalone are high relative to other aquaculture species. This was attributed primarily to small effective population sizes produced by a combination of natural- and anthropogenic factors. The decay of LD with genetic distance was evident in both cultured cohorts, but almost absent in wild cohorts, likely reflecting the differences in size, age and sampling of wild populations relative to cultured. Putative evidence for the effects of recombination, selection, and epistasis were also evident in distinctive locus-specific patterns of LD on some of the linkage groups, many of which could represent the effects of domestication. The effects of selection associated with the domestication event were further investigated using a candidate locus LD mapping approach to determine the proportion of candidate loci under selection associated with artificial selection for faster growth rate in cultured abalone. Two loci (15%) were found to be significantly associated with differences in size of individual animals, both of which could be linked with genes potentially involved in growth and development. These markers could therefore find application in MAS programmes for abalone. Several promising candidates for natural selection were also identified based on similarity with known genes. As the latter represented the majority, natural selection, rather than artificial selection, appears to be predominant during the early stages of domestication in abalone. While some conclusions within the current study were speculative, both the direct and indirect applications of LD were clearly demonstrated. Linkage disequilibrium data can provide a unique perspective on many of the commonly used population genetic estimates, and is therefore of great value in population genetic investigations. Furthermore, these results also highlighted the effectiveness of the candidate locus approach in species with both limited molecular resources and extensive LD.
AFRIKAANSE OPSOMMING: Koppelingsonewewig (KO) word gedefinieer as die nie-lukrake assosiasie van allele by twee of meer lokusse binne 'n populasie. Koppelingsonewewig is sensitief vir 'n verskeidenheid van lokus-spesifieke- en demografiese faktore, en kan dus insiggewend wees m.b.t. mikro-evolusionêre faktore wat spesies van belang beïnvloed het. Dit kan ook benut word om die genoom-gebiede onderligend tot komplekse eienskappe te bespeur; wat dan aangewend kan word vir prestasie-evaluering m.b.v. merkerbemiddelde seleksie (MBS). Die Suid-Afrikaanse perlemoen, Haliotis midae, ondersteun 'n vinnig ontwikkelende akwakultuur produksie bedryf, waarin genetiese verbeteringspotensiaal hoog is. Hierdie spesie verteenwoordig ook 'n opportunistiese model vir die bestudering van die gevolge van vroeë domestiseering in 'n skulpvis spesie. Die doel van hierdie studie was dus om vlakke van genoom-wye KO binne die Suid-Afrikaanse perlemoen te kwantifiseer en te karakteriseer, en om die toepassing hiervan binne populasiegenetiese ondersoeke en die karakterisering van komplekse eienskappe te demonstreer. Ramings van KO tussen 112 gekarteerde mikrosatelliet-merkers binne wilde en gekultiveerde H. midae het aan die lig gebring dat die vlakke van KO in perlemoen hoog was, in vergelyking met ander akwakultuur spesies. Dit word hoofsaaklik toegeskryf aan klein effektiewe populasiegroottes wat deur 'n kombinasie van natuurlike- en antropogeniese faktore teweeg gebring word. Die verval van KO met genetiese afstand was duidelik waarneembaar in gekultiveerde kohorte, maar amper afwesig in die wilde kohorte, waarskynlik a.g.v. verskille in populasiegrootte, ouderdom, en streekproef-neemings metodieke van die verskeie populasies. Vermeende bewyse vir die gevolge van rekombinasie, seleksie en epistase kon ook gesien word a.g.v. lokus-spesifieke patrone van KO op sommige van die koppelingsgroepe, moontlik ‘n gevolg van domestisering. Die gevolge van seleksie wat verband hou met die domestiseringsgebeurtenis is verder ondersoek m.b.v 'n kandidaat-lokus KO karteringsbenadering om die verhouding van kandidaat lokusse wat geassosieer is met kunsmatige seleksie (vir vinniger groeikoers in perlemoen) te bepaal. Twee lokusse (15%) was beduidend geassosieer met verskille in grootte tussen individuele diere. Beide van die lokusse was gekoppel met gene wat potensieel betrokke is by groei en ontwikkeling. Hierdie merkers kan dus moontlik aangewend word in MBS programme vir perlemoen. Verskeie belowende kandidaat lokusse vir natuurlike seleksie is ook geïdentifiseer gebaseer op ooreenkoms met bekende gene. Gegewe dat die laasgenoemde die meerderheid van die merkers verteenwoordig, kan daar afgelei word dat natuurlike seleksie, eerder as kunsmatige seleksie, oorheersend is in die vroeë stadia van domestisering in perlemoen. Terwyl sommige gevolgtrekkings binne die huidige studie spekulatief was, is beide die direkte en indirekte toepassings van KO duidelik gedemonstreer. Koppelingsonewewig-data kan 'n unieke perspektief gee op baie van die algemeen gebruikte populasie genetiese skattings, en is dus van groot waarde in populasie genetiese ondersoeke. Verder demonstreer hierdie resultate ook die doeltreffendheid van die kandidaat lokus benadering in spesies met beide beperkte molekulêre hulpbronne en uitgebreide KO.

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Sjölander, Anders. "Exploring linkage disequilibrium to date admixture using ancient DNA". Thesis, Uppsala universitet, Växtekologi och evolution, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-298198.

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Admixture studies based on contemporary DNA are well studied and results from these have shown to correlate well with other evidence. The study of using ancient DNA for determining admixture times is a less explored alternative for determining admixture. Admixture-induced Linkage Disequilibrium for Evolutionary Relationships (ALDER) is an established tool for determining admixture time from contemporary DNA. This project investigates the use of ALDER on simulated ancient DNA to determine if it can be used in actual ancient DNA studies. The results from this project suggest that ALDER can be used in actual studies, with good accuracy and reliability.

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Webb, Adam J. "Meiotic recombination and linkage disequilibrium in the human genome". Thesis, University of Leicester, 2006. http://hdl.handle.net/2381/30369.

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Evidence is accumulating that recombination events in humans are not randomly distributed, but clustered into hotspots 1-2 kb wide. The Xp/Yp pseudoautosomal region (PAR1) is a male-specific recombination hot domain. The PAR1 gene PPP2R3B shows unusually high levels of nucleotide diversity. I have used LD studies in this region to reveal a dearth of historical recombination, arguing against earlier speculation that high diversity is driven by mutagenic recombination. Chimp LD studies, the existence of recombination hotspots inside LD blocks, and the observation of meiotic drive within a hotspot favouring recombination suppressors all support the hypothesis that recombination hotspots turn over rapidly during evolution. To identify very recently arisen recombination hotspots, LD patterns between African-American and European-American populations were compared in 147 genes, revealing PON2 as the only gene with convincing evidence for a recently arisen recombination hotspot. A second approach, whereby contemporary linkage data is compared to historical LD data, was employed to identify putative young recombination hotspots. The 6 kb D6S383-D6S970 interval on chromosome 6 shows a recombination rate of 33 cM/Mb in pedigrees, yet lies within a block of strong LD. Sperm crossover analyses across this region in two men did not reveal a recombination hotspot, raising the possibility of a hotspot polymorphism at this locus. Finally, the release of data from phase II of the HapMap project allowed construction of genome-wide linkage disequilibrium unit (LDU) maps at high resolution. Sliding window analyses of these maps suggested putative recombination hotspots, directing future research into the characteristics and distribution of recombination hotspots in humans.

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Libri sul tema "Linkage disequilibrium"

Andrew, Collins R. Linkage Disequilibrium and Association Mapping. New Jersey: Humana Press, 2007. http://dx.doi.org/10.1385/1597453897.

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Collins, Andrew R., a cura di. Linkage Disequilibrium and Association Mapping. Totowa, NJ: Humana Press, 2007. http://dx.doi.org/10.1007/978-1-59745-389-9.

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Collins, Andrew R. Linkage Disequilibrium and Association Mapping. Gardners Books, 2010.

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A, Collins, a cura di. Linkage disequilibrium and association mapping: Analysis and applications. Totowa, N.J: Humana Press, 2007.

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Linkage disequilibrium and association mapping: Analysis and applications. Totowa, NJ: Humana Press, 2008.

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Xie, Fang. Simultaneous detection of linkage and linkage disequilibrium for families with an affected sib-pair. 2003.

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Collins, Andrew R. Linkage Disequilibrium and Association Mapping: Analysis and Applications (Methods in Molecular Biology). Humana Press, 2007.

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Walsh, Bruce, e Michael Lynch. Short-term Changes in the Variance: 1. Changes in the Additive Variance. Oxford University Press, 2018. http://dx.doi.org/10.1093/oso/9780198830870.003.0016.

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Selection changes the additive-genetic variance (and hence the response in the mean) by both changing allele frequencies and by generating correlations among alleles at different loci (linkage disequilibrium). Such selection-induced correlations can be generated even between unlinked loci, and (generally) are negative, such that alleles increasing trait values tend to become increasingly negative correlated under direction or stabilizing selection, and positively correlated under disruptive selection. Such changes in the additive-genetic variance from disequilibrium is called the Bulmer effects. For a large number of loci, the amount of change can be predicted from the Bulmer equation, the analog of the breeder's equation, but now for the change in the variance. Upon cessation of selection, any disequilibrium decays away, and the variances revert back to their additive-genic variances (the additive variance in the absence of disequilibrium). Assortative mating also generates such disequilibrium.

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Walsh, Bruce, e Michael Lynch. Selection Under Inbreeding. Oxford University Press, 2018. http://dx.doi.org/10.1093/oso/9780198830870.003.0023.

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When dominance is presence, the selection response equations under inbreeding can become rather complex, they require additional variance components beyond the additive-genetic variance. Further, both transient and permanent components of response can arise. This chapter examines the theory of both the covariance of relatives under general inbreeding, as well as the expected selection response under inbreeding. Due to the decrease in the effective recombination rate under selfing, the Bulmer effect can be rather dramatic, as any linkage disequilibrium generated by selection is only weakly removed by recombination. Finally, this chapter also examines the evolutionary forces that interact to determine the selfing rate for a given population.

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Walsh, Bruce, e Michael Lynch. Analysis of Short-term Selection Experiments: 2. Mixed-model and Bayesian Approaches. Oxford University Press, 2018. http://dx.doi.org/10.1093/oso/9780198830870.003.0019.

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When the full pedigree of individuals whose values (records) were used in the selection decisions during an experiment (or breeding program) is known, LS analysis can be replaced by mixed models and their Bayesian extensions. In this setting, REML can be used to estimate genetic variances and BLUP can be used to estimate the mean breeding value in any given generation. The latter allows for genetic trends to be separated from environmental trends without the need for a control population. Under the infinitesimal model setting (wherein selection-induced allele-frequency changes are small during the course of the experiment), the use of the relationship matrix in a BLUP analysis accounts for drift, nonrandom mating, and linkage disequilibrium.

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Capitoli di libri sul tema "Linkage disequilibrium"

Oraguzie, Nnadozie C., Phillip L. Wilcox, Erik H. A. Rikkerink e H. Nihal de Silva. "Linkage Disequilibrium". In Association Mapping in Plants, 11–39. New York, NY: Springer New York, 2007. http://dx.doi.org/10.1007/978-0-387-36011-9_2.

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Earp, Madalene A., e Ellen L. Goode. "Linkage Disequilibrium". In Encyclopedia of Cancer, 1–8. Berlin, Heidelberg: Springer Berlin Heidelberg, 2014. http://dx.doi.org/10.1007/978-3-642-27841-9_3368-3.

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Earp, Madalene A., e Ellen L. Goode. "Linkage Disequilibrium". In Encyclopedia of Cancer, 2496–502. Berlin, Heidelberg: Springer Berlin Heidelberg, 2017. http://dx.doi.org/10.1007/978-3-662-46875-3_3368.

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Goode, Ellen L. "Linkage Disequilibrium". In Encyclopedia of Cancer, 2043–48. Berlin, Heidelberg: Springer Berlin Heidelberg, 2011. http://dx.doi.org/10.1007/978-3-642-16483-5_3368.

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Slatkin, Montgomery. "Linkage Disequilibrium". In Human Population Genomics, 31–45. Cham: Springer International Publishing, 2021. http://dx.doi.org/10.1007/978-3-030-61646-5_2.

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Mukhopadhyay, Amrita. "Linkage Disequilibrium". In Encyclopedia of Sexual Psychology and Behavior, 1–5. Cham: Springer International Publishing, 2023. http://dx.doi.org/10.1007/978-3-031-08956-5_1340-1.

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de Silva, H. Nihal, e Roderick D. Ball. "Linkage Disequilibrium Mapping Concepts". In Association Mapping in Plants, 103–32. New York, NY: Springer New York, 2007. http://dx.doi.org/10.1007/978-0-387-36011-9_7.

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Collins, Andrew R. "Linkage Disequilibrium and Association Mapping". In Linkage Disequilibrium and Association Mapping, 1–15. Totowa, NJ: Humana Press, 2007. http://dx.doi.org/10.1007/978-1-59745-389-9_1.

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McVean, G. "Linkage Disequilibrium, Recombination and Selection". In Handbook of Statistical Genetics, 909–44. Chichester, UK: John Wiley & Sons, Ltd, 2008. http://dx.doi.org/10.1002/9780470061619.ch27.

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Shugart, Yin Yao, Lina Chen, Rui Li e Terri Beaty. "Family-Based Linkage Disequilibrium Tests Using General Pedigrees". In Linkage Disequilibrium and Association Mapping, 141–49. Totowa, NJ: Humana Press, 2007. http://dx.doi.org/10.1007/978-1-59745-389-9_10.

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Atti di convegni sul tema "Linkage disequilibrium"

Alachiotis, Nikolaos, e Gabriel Weisz. "High Performance Linkage Disequilibrium". In FPGA'16: The 2016 ACM/SIGDA International Symposium on Field-Programmable Gate Arrays. New York, NY, USA: ACM, 2016. http://dx.doi.org/10.1145/2847263.2847271.

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Ao, S. I., Sio-Iong Ao, Mahyar A. Amouzegar e Su-Shing Chen. "Constructing Linkage Disequilibrium Map with Iterative Approach". In WORLD CONGRESS ON ENGINEERING AND COMPUTER SCIENCE. AIP, 2008. http://dx.doi.org/10.1063/1.2937607.

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Lu, Jun, Jun Li, Ruiqing Jing, Qiong Wang, Cheng Chang e Jiaxing Guo. "Research on Linkage Disequilibrium Method Based on OpenMP". In 2016 3rd International Conference on Information Science and Control Engineering (ICISCE). IEEE, 2016. http://dx.doi.org/10.1109/icisce.2016.230.

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Yeo, Sang-Soo, e Sung Kwon Kim. "MarSelHR: A Haplotype Reconstruction System Using Linkage Disequilibrium". In 2007 Frontiers in the Convergence of Bioscience and Information Technologies. IEEE, 2007. http://dx.doi.org/10.1109/fbit.2007.142.

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COLLINS, A. "LINKAGE DISEQUILIBRIUM MAPPING USING SINGLE NUCLEOTIDE POLYMORPHISMS -WHICH POPULATION?" In Proceedings of the Pacific Symposium. WORLD SCIENTIFIC, 1999. http://dx.doi.org/10.1142/9789814447331_0063.

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Ibrahim, Zina M., Stephen Newhouse e Richard Dobson. "Detecting epistasis in the presence of linkage disequilibrium: A focused comparison". In 2013 IEEE Symposium on Computational Intelligence in Bioinformatics and Computational Biology (CIBCB). IEEE, 2013. http://dx.doi.org/10.1109/cibcb.2013.6595394.

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Theodoris, Charalampos, Nikolaos Alachiotis, Tze Meng Low e Pavlos Pavlidis. "qLD: High-performance Computation of Linkage Disequilibrium on CPU and GPU". In 2020 IEEE 20th International Conference on Bioinformatics and Bioengineering (BIBE). IEEE, 2020. http://dx.doi.org/10.1109/bibe50027.2020.00019.

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RANNALA, B., e J. P. REEVE. "JOINT BAYESIAN ESTIMATION OF MUTATION LOCATION AND AGE USING LINKAGE DISEQUILIBRIUM". In Proceedings of the Pacific Symposium. WORLD SCIENTIFIC, 2002. http://dx.doi.org/10.1142/9789812776303_0049.

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Hernández-Lemus, Enrique, Jesús K. Estrada-Gil, Irma Silva-Zolezzi, J. Carlos Fernández-López, Alfredo Hidalgo-Miranda, Gerardo Jiménez-Sánchez, Leonardo Dagdug e Leopoldo Gracía-Colin S. "Nonlinear Analysis of Time Series in Genome-Wide Linkage Disequilibrium Data". In COMPLIFE 2007: The Third International Symposium on Computational Life Science. AIP, 2008. http://dx.doi.org/10.1063/1.2891412.

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ZHANG, SHUANGLIN, KUI ZHANG, JINMING LI e HONGYU ZHAO. "ON A FAMILY-BASED HAPLOTYPE PATTERN MINING METHOD FOR LINKAGE DISEQUILIBRIUM MAPPING". In Proceedings of the Pacific Symposium. WORLD SCIENTIFIC, 2001. http://dx.doi.org/10.1142/9789812799623_0010.

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Rapporti di organizzazioni sul tema "Linkage disequilibrium"

Sun, Xiaochen, Rohan L. Fernando, Dorian J. Garrick e Jack C. M. Dekkers. Genomic Prediction Using Linkage Disequilibrium and Co-segregation. Ames (Iowa): Iowa State University, gennaio 2013. http://dx.doi.org/10.31274/ans_air-180814-1253.

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Medrano, Juan, Adam Friedmann, Moshe (Morris) Soller, Ehud Lipkin e Abraham Korol. High resolution linkage disequilibrium mapping of QTL affecting milk production traits in Israel Holstein dairy cattle. United States Department of Agriculture, marzo 2008. http://dx.doi.org/10.32747/2008.7696509.bard.

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Original objectives: To create BAC contigs covering two QTL containing chromosomal regions (QTLR) and obtain BAC end sequence information as a platform for SNP identification. Use the SNPs to search for marker-QTL linkage disequilibrium (LD) in the test populations (US and Israel Holstein cattle). Identify candidate genes, test for association with dairy cattle production and functional traits, and confirm any associations in a secondary test population. Revisions in the course of the project: The selective recombinant genotyping (SRG) methodology which we implemented to provide moderate resolution QTL mapping turned out to be less effective than expected, due to problems introduced by incomplete marker informativity. This required a no-cost one-year extension of the project. Aside from this, the project was implemented essentially as envisaged, but only with respect to a single QTLR and single population association-test. Background to the topic. Dairy cattle breeders are looking to marker-assisted selection (MAS) as a means of identifying genetically superior sires and dams. MAS based on population-wide LD can be many times more effective than MAS based on within-family linkage mapping. In this proposal we developed a protocol leading from family based QTL mapping to population-wide LD between markers and the QTL Major conclusions, solutions, achievements. The critical importance of marker informativity for application of the SRG design in outcrossing random mating populations was identified, and an alternative Fractioned Pool Design (FPD) based on selective DNA pooling was developed. We demonstrated the feasibility of constructing a BAC contig across a targeted chromosomal region flanking the marker RM188 on bovine chromosome BTA4, which was shown in previous work to contain a QTL affecting milk production traits. BAC end sequences were obtained and successfully screened for SNPs. LD studies of these SNPs in the Israel population, and of an independent set of SNPs taken across the entire proximal region of BTA4 in the USA population, showed a much lower degree of LD than previously reported in the literature. Only at distances in the sub-cM level did an appreciable fraction of SNP marker-pairs show levels of LD useful for MAS. In contrast, studies in the Israel population using microsatellite markers, presented an equivalent degree of LD at a 1-5 separation distance. SNP LD appeared to reflect historical population size of Bostaurus (Ne=5000- 10,000), while microsatellite LD appeared to be in proportion to more recent effective population size of the Holstein breed (Ne=50-100). An appreciable fraction of the observed LD was due to Family admixture structure of the Holstein population. The SNPs MEOX2/IF2G (found within the gene SETMAR at 23,000 bp from RM188) and SNP23 were significantly associated with PTA protein, Cheese dollars and Net Merit Protein in the Davis bull resource population, and were also associated with protein and casein percentages in the Davis cow resource population. Implications. These studies document a major difference in degree of LD presented by SNPs as compared to microsatellites, and raise questions as to the source of this difference and its implications for QTL mapping and MAS. The study lends significant support to the targeted approach to fine map a previously identified QTL. Using high density genotyping with SNP discovered in flanking genes to the QTL, we have identified important markers associated with milk protein percentage that can be tested in markers assisted selection programs.

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Sela, Hanan, Eduard Akhunov e Brian J. Steffenson. Population genomics, linkage disequilibrium and association mapping of stripe rust resistance genes in wild emmer wheat, Triticum turgidum ssp. dicoccoides. United States Department of Agriculture, gennaio 2014. http://dx.doi.org/10.32747/2014.7598170.bard.

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The primary goals of this project were: (1) development of a genetically characterized association panel of wild emmer for high resolution analysis of the genetic basis of complex traits; (2) characterization and mapping of genes and QTL for seedling and adult plant resistance to stripe rust in wild emmer populations; (3) characterization of LD patterns along wild emmer chromosomes; (4) elucidation of the multi-locus genetic structure of wild emmer populations and its correlation with geo-climatic variables at the collection sites. Introduction In recent years, Stripe (yellow) rust (Yr) caused by Pucciniastriiformis f. sp. tritici(PST) has become a major threat to wheat crops in many parts of the world. New races have overcome most of the known resistances. It is essential, therefore, that the search for new genes will continue, followed by their mapping by molecular markers and introgression into the elite varieties by marker-assisted selection (MAS). The reservoir of genes for disease and pest resistance in wild emmer wheat (Triticumdicoccoides) is an important resource that must be made available to wheat breeders. The majority of resistance genes that were introgressed so far in cultivated wheat are resistance (R) genes. These genes, though confering near-immunity from the seedling stage, are often overcome by the pathogen in a short period after being deployed over vast production areas. On the other hand, adult-plant resistance (APR) is usually more durable since it is, in many cases, polygenic and confers partial resistance that may put less selective pressure on the pathogen. In this project, we have screened a collection of 480 wild emmer accessions originating from Israel for APR and seedling resistance to PST. Seedling resistance was tested against one Israeli and 3 North American PST isolates. APR was tested on accessions that did not have seedling resistance. The APR screen was conducted in two fields in Israel and in one field in the USA over 3 years for a total of 11 replicates. We have found about 20 accessions that have moderate stripe rust APR with infection type (IT<5), and about 20 additional accessions that have novel seedling resistance (IT<3). We have genotyped the collection using genotyping by sequencing (GBS) and the 90K SNP chip array. GBS yielded a total 341K SNP that were filtered to 150K informative SNP. The 90K assay resulted in 11K informative SNP. We have conducted a genome-wide association scan (GWAS) and found one significant locus on 6BL ( -log p >5). Two novel loci were found for seedling resistance. Further investigation of the 6BL locus and the effect of Yr36 showed that the 6BL locus and the Yr36 have additive effect and that the presence of favorable alleles of both loci results in reduction of 2 grades in the IT score. To identify alleles conferring adaption to extreme climatic conditions, we have associated the patterns of genomic variation in wild emmer with historic climate data from the accessions’ collection sites. The analysis of population stratification revealed four genetically distinct groups of wild emmer accessions coinciding with their geographic distribution. Partitioning of genomic variance showed that geographic location and climate together explain 43% of SNPs among emmer accessions with 19% of SNPs affected by climatic factors. The top three bioclimatic factors driving SNP distribution were temperature seasonality, precipitation seasonality, and isothermality. Association mapping approaches revealed 57 SNPs associated with these bio-climatic variables. Out of 21 unique genomic regions controlling heading date variation, 10 (~50%) overlapped with SNPs showing significant association with at least one of the three bioclimatic variables. This result suggests that a substantial part of the genomic variation associated with local adaptation in wild emmer is driven by selection acting on loci regulating flowering. Conclusions: Wild emmer can serve as a good source for novel APR and seedling R genes for stripe rust resistance. APR for stripe rust is a complex trait conferred by several loci that may have an additive effect. GWAS is feasible in the wild emmer population, however, its detection power is limited. A panel of wild emmer tagged with more than 150K SNP is available for further GWAS of important traits. The insights gained by the bioclimatic-gentic associations should be taken into consideration when planning conservation strategies.

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Foulkes, William D. Locating a Prostate Cancer Susceptibility Gene on the X Chromosome by Linkage Disequilibrium Mapping Using Three Founder Populationin Quebec and Switzerland. Fort Belvoir, VA: Defense Technical Information Center, marzo 2004. http://dx.doi.org/10.21236/ada426100.

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Foulkee, William D. Locating a Prostate Cancer Susceptibility Gene on the X Chromosome by Linkage Disequilibrium Mapping Using Three Founder Populations in Quebec and Switzerland. Fort Belvoir, VA: Defense Technical Information Center, marzo 2005. http://dx.doi.org/10.21236/ada443199.

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Foulkes, William D. Locating a Prostate Cancer Susceptibility Gene on the X Chromosome by Linkage Disequilibrium Mapping Using Three Founder Populations in Quebec and Switzerland. Fort Belvoir, VA: Defense Technical Information Center, marzo 2002. http://dx.doi.org/10.21236/ada405914.

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Beach, Erin, Behnam Abasht, Rohan L. Fernando, Jack C. M. Dekkers, Susan J. Lamont, Jesus Arango, Petek Settar, Janet Fulton e Neil P. O'Sullivan. Extent and Consistency of Linkage Disequilibrium and Identification of DNA Markers for Production and Egg Quality Traits in Commercial Layer Chicken Populations. Ames (Iowa): Iowa State University, gennaio 2009. http://dx.doi.org/10.31274/ans_air-180814-817.

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Weller, Joel I., Harris A. Lewin e Micha Ron. Determination of Allele Frequencies for Quantitative Trait Loci in Commercial Animal Populations. United States Department of Agriculture, febbraio 2005. http://dx.doi.org/10.32747/2005.7586473.bard.

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Individual loci affecting economic traits in dairy cattle (ETL) have been detected via linkage to genetic markers by application of the granddaughter design in the US population and the daughter design in the Israeli population. From these analyses it is not possible to determine allelic frequencies in the population at large, or whether the same alleles are segregating in different families. We proposed to answer this question by application of the "modified granddaughter design", in which granddaughters with a common maternal grandsire are both genotyped and analyzed for the economic traits. The objectives of the proposal were: 1) to fine map three segregating ETL previously detected by a daughter design analysis of the Israeli dairy cattle population; 2) to determine the effects of ETL alleles in different families relative to the population mean; 3) for each ETL, to determine the number of alleles and allele frequencies. The ETL on Bostaurusautosome (BT A) 6 chiefly affecting protein concentration was localized to a 4 cM chromosomal segment centered on the microsatellite BM143 by the daughter design. The modified granddaughter design was applied to a single family. The frequency of the allele increasing protein percent was estimated at 0.63+0.06. The hypothesis of equal allelic frequencies was rejected at p<0.05. Segregation of this ETL in the Israeli population was confirmed. The genes IBSP, SPP1, and LAP3 located adjacent to BM143 in the whole genome cattle- human comparative map were used as anchors for the human genome sequence and bovine BAC clones. Fifteen genes within 2 cM upstream of BM143 were located in the orthologous syntenic groups on HSA4q22 and HSA4p15. Only a single gene, SLIT2, was located within 2 cM downstream of BM143 in the orthologous HSA4p15 region. The order of these genes, as derived from physical mapping of BAC end sequences, was identical to the order within the orthologous syntenic groups on HSA4: FAM13A1, HERC3. CEB1, FLJ20637, PP2C-like, ABCG2, PKD2. SPP, MEP, IBSP, LAP3, EG1. KIAA1276, HCAPG, MLR1, BM143, and SLIT2. Four hundred and twenty AI bulls with genetic evaluations were genotyped for 12 SNPs identified in 10 of these genes, and for BM143. Seven SNPs displayed highly significant linkage disequilibrium effects on protein percentage (P<0.000l) with the greatest effect for SPP1. None of SNP genotypes for two sires heterozygous for the ETL, and six sires homozygous for the ETL completely corresponded to the causative mutation. The expression of SPP 1 and ABCG2 in the mammary gland corresponded to the lactation curve, as determined by microarray and QPCR assays, but not in the liver. Anti-sense SPP1 transgenic mice displayed abnormal mammary gland differentiation and milk secretion. Thus SPP 1 is a prime candidate gene for this ETL. We confirmed that DGAT1 is the ETL segregating on BTA 14 that chiefly effects fat concentration, and that the polymorphism is due to a missense mutation in an exon. Four hundred Israeli Holstein bulls were genotyped for this polymorphism, and the change in allelic frequency over the last 20 years was monitored.

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Freeman, Stanley, e Daniel Legard. Epidemiology and Etiology of Colletotrichum Species Causing Strawberry Diseases. United States Department of Agriculture, settembre 2001. http://dx.doi.org/10.32747/2001.7695845.bard.

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Diseases caused by Colletotrichum spp. are one of the most important limitations on international strawberry production, affecting all vegetative and fruiting parts of the plant. From 1995 to 1997, C. acutatum infections reached epidemic levels in Israeli strawberry nurseries, causing extensive loss of transplants in fruit-bearing fields and additional reductions in yield. Although C. acutatum also occurs on strawberry in Florida, recent crown rot epidemics have been primarily caused by C. gloeosporioides. Little is known about the basic epidemiology of these important diseases on strawberry. The source of initial inoculum for epidemics in Israel, Florida (other US states including California) and the rest of the world is not well understood. Subspecies relationships between Colletotrichum isolates that cause the different diseases on strawberry (i.e. attack different tissues) are also not well understood. Objectives of this proposal were to detennine the potential of infested soil, strawberry debris and other hosts as sources of primary inoculum for strawberry diseases caused by Colletotrichum spp. in Israel and Florida. In addition, traditional (ie. morphological characteristics, benomyl sensitivity, vegetative compatibility grouping) and DNA based methods were used to investigate the etiology of these diseases in order to resolve epidemiologically important subspecies variation. In Israel it was found that C. gloeosporioides and C. acutatum infecting strawberry could remain viable in sterilized soil for up to one year and in methyl-bromide fumigated soil for up to 4 months; inoculum in mummified fruit remained viable for at least 5 months under field conditions whereas that in infected crowns was not recovered. Therefore, the contribution of these inocula to disease epidemics should be considered. The host range and specificity of C. acutatum from strawberry was examined on pepper, eggplant, tomato, bean and strawberry under greenhouse conditions. The fungus was recovered from all plant species over a three-month period but caused disease symptoms only on strawberry. C. acutatum was also isolated from healthy looking, asymptomatic plants of the weed species, Vicia and Conyza, growing in infected strawberry fruiting fields. Isolates of C. acutatum originating from strawberry and anemone infected both plant species in artificial inoculations. The habitation of a large number of plant species including weeds by C. acutatum suggests that although it causes disease only on strawberry and anemone in Israel, these plants may serve as a potential inoculum source for strawberry infection and pennit survival of the pathogen between seasons. In Florida, isolates of Colletotrichum spp. from diseased strawberry fruit and crowns were evaluated to detennine their etiology and the genetic diversity of the pathogens. Only C. acutatum was recovered from fruit and C. gloeosporioides were the main species recovered from crowns. These isolates were evaluated at 40 putative genetic loci using random amplified polymorphic DNA (RAPD). Genetic analysis of RAPD markers revealed that the level of linkage disequilibrium among polymorphic loci in C. gloeosporioides suggested that they were a sexually reproducing population. Under field conditions in Florida, it was detennined that C. gloeosporioides in buried crowns survived

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