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On the Quantitative Genetics of Mixture Characters

Gianola, Daniel; Heringstad, Bjorg; Odegaard, Jorgen
Fonte: Copyright © 2006 by the Genetics Society of America Publicador: Copyright © 2006 by the Genetics Society of America
Tipo: Artigo de Revista Científica
Publicado em /08/2006 EN
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Finite mixture models are helpful for uncovering heterogeneity due to hidden structure. Quantitative genetics issues of continuous characters having a finite mixture of Gaussian components as statistical distribution are explored in this article. The partition of variance in a mixture, the covariance between relatives under the supposition of an additive genetic model, and the offspring–parent regression are derived. Formulas for assessing the effect of mass selection operating on a mixture are given. Expressions for the genetic and phenotypic correlations between mixture and Gaussian traits and between two mixture traits are presented. It is found that, if there is heterogeneity in a population at the genetic or environmental level, then genetic parameters based on theory treating distributions as homogeneous can lead to misleading interpretations. Some peculiarities of mixture characters are: heritability depends on the mean values of the component distributions, the offspring–parent regression is nonlinear, and genetic or phenotypic correlations cannot be interpreted devoid of the mixture proportions and of the parameters of the distributions mixed.

A Common Haplotype of the Glucokinase Gene Alters Fasting Glucose and Birth Weight: Association in Six Studies and Population-Genetics Analyses

Weedon, Michael N. ; Clark, Vanessa J. ; Qian, Yudong ; Ben-Shlomo, Yoav ; Timpson, Nicholas ; Ebrahim, Shah ; Lawlor, Debbie A. ; Pembrey, Marcus E. ; Ring, Susan ; Wilkin, Terry J. ; Voss, Linda D. ; Jeffery, Alison N. ; Metcalf, Brad
Fonte: The American Society of Human Genetics Publicador: The American Society of Human Genetics
Tipo: Artigo de Revista Científica
EN
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Fasting glucose is associated with future risk of type 2 diabetes and ischemic heart disease and is tightly regulated despite considerable variation in quantity, type, and timing of food intake. In pregnancy, maternal fasting glucose concentration is an important determinant of offspring birth weight. The key determinant of fasting glucose is the enzyme glucokinase (GCK). Rare mutations of GCK cause fasting hyperglycemia and alter birth weight. The extent to which common variation of GCK explains normal variation of fasting glucose and birth weight is not known. We aimed to comprehensively define the role of variation of GCK in determination of fasting glucose and birth weight, using a tagging SNP (tSNP) approach and studying 19,806 subjects from six population-based studies. Using 22 tSNPs, we showed that the variant rs1799884 is associated with fasting glucose at all ages in the normal population and exceeded genomewide levels of significance (P=10-9). rs3757840 was also highly significantly associated with fasting glucose (P=8×10-7), but haplotype analysis revealed that this is explained by linkage disequilibrium (r2=0.2) with rs1799884. A maternal A allele at rs1799884 was associated with a 32-g (95% confidence interval 11–53 g) increase in offspring birth weight (P=.002). Genetic variation influencing birth weight may have conferred a selective advantage in human populations. We performed extensive population-genetics analyses to look for evidence of recent positive natural selection on patterns of GCK variation. However...

Multilevel Selection 1: Quantitative Genetics of Inheritance and Response to Selection

Bijma, Piter; Muir, William M.; Van Arendonk, Johan A. M.
Fonte: Copyright © 2007 by the Genetics Society of America Publicador: Copyright © 2007 by the Genetics Society of America
Tipo: Artigo de Revista Científica
Publicado em /01/2007 EN
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Interaction among individuals is universal, both in animals and in plants, and substantially affects evolution of natural populations and responses to artificial selection in agriculture. Although quantitative genetics has successfully been applied to many traits, it does not provide a general theory accounting for interaction among individuals and selection acting on multiple levels. Consequently, current quantitative genetic theory fails to explain why some traits do not respond to selection among individuals, but respond greatly to selection among groups. Understanding the full impacts of heritable interactions on the outcomes of selection requires a quantitative genetic framework including all levels of selection and relatedness. Here we present such a framework and provide expressions for the response to selection. Results show that interaction among individuals may create substantial heritable variation, which is hidden to classical analyses. Selection acting on higher levels of organization captures this hidden variation and therefore always yields positive response, whereas individual selection may yield response in the opposite direction. Our work provides testable predictions of response to multilevel selection and reduces to classical theory in the absence of interaction. Statistical methodology provided elsewhere enables empirical application of our work to both natural and domestic populations.

Molecular Genetics and Genomic Analysis of Scytonemin Biosynthesis in Nostoc punctiforme ATCC 29133▿

Soule, Tanya; Stout, V.; Swingley, W. D.; Meeks, J. C.; Garcia-Pichel, F.
Fonte: American Society for Microbiology Publicador: American Society for Microbiology
Tipo: Artigo de Revista Científica
EN
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The indole-alkaloid scytonemin is the most common and widespread sunscreen among cyanobacteria. Previous research has focused on its nature, distribution, ecology, physiology, and biochemistry, but its molecular genetics have not been explored. In this study, a scytonemin-deficient mutant of the cyanobacterium Nostoc punctiforme ATCC 29133 was obtained by random transposon insertion into open reading frame NpR1273. The absence of scytonemin under conditions of induction by UV irradiation was the single phenotypic difference detected in a comparative analysis of the wild type and the mutant. A cause-effect relationship between the phenotype and the mutation in NpR1273 was demonstrated by constructing a second scytoneminless mutant through directed mutagenesis of that gene. The genomic region flanking the mutation revealed an 18-gene cluster (NpR1276 to NpR1259). Four putative genes in the cluster, NpR1274 to NpR1271, with no previously known functions, are likely to be involved in the assembly of scytonemin. Also in this cluster, there is a redundant set of genes coding for shikimic acid and aromatic amino acid biosynthesis enzymes, leading to the production of tryptophan and tyrosine, which are likely to be biosynthetic precursors of the sunscreen.

Molecular Population Genetics of Drosophila Subtelomeric DNA

Anderson, Jennifer A.; Song, Yun S.; Langley, Charles H.
Fonte: Genetics Society of America Publicador: Genetics Society of America
Tipo: Artigo de Revista Científica
Publicado em /01/2008 EN
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DNA sequence surveys in yeast and humans suggest that the forces shaping telomeric polymorphism and divergence are distinctly more dynamic than those in the euchromatic, gene-rich regions of the chromosomes. However, the generality of this pattern across outbreeding, multicellular eukaryotes has not been determined. To characterize the structure and evolution of Drosophila telomeres, we collected and analyzed molecular population genetics data from the X chromosome subtelomere in 58 lines of North American Drosophila melanogaster and 29 lines of African D. melanogaster. We found that Drosophila subtelomeres exhibit high levels of both structural and substitutional polymorphism relative to linked euchromatic regions. We also observed strikingly different patterns of variation in the North American and African samples. Moreover, our analyses of the polymorphism data identify a localized hotspot of recombination in the most-distal portion of the X subtelomere. While the levels of polymorphism decline sharply and in parallel with rates of crossing over per physical length over the distal first euchromatic megabase pairs of the X chromosome, our data suggest that they rise again sharply in the subtelomeric region (≈80 kbp). These patterns of historical recombination and geographic differentiation indicate that...

Comparative Genetics of Hybrid Incompatibility: Sterility in Two Solanum Species Crosses

Moyle, Leonie C.; Nakazato, Takuya
Fonte: Genetics Society of America Publicador: Genetics Society of America
Tipo: Artigo de Revista Científica
Publicado em /07/2008 EN
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The genetic basis of hybrid sterility can provide insight into the genetic and evolutionary origins of species barriers. We examine the genetics of hybrid incompatibility between two diploid plant species in the plant clade Solanum sect. Lycopersicon. Using a set of near-isogenic lines (NILs) representing the wild species Solanum pennellii (formerly Lycopersicon pennellii) in the genetic background of the cultivated tomato S. lycopersicum (formerly L. esculentum), we found that hybrid pollen and seed infertility are each based on a modest number of loci, male (pollen) and other (seed) incompatibility factors are roughly comparable in number, and seed-infertility QTL act additively or recessively. These findings are remarkably consistent with our previous analysis in a different species pair, S. lycopersicum × S. habrochaites. Data from both studies contrast strongly with data from Drosophila. Finally, QTL for pollen and seed sterility from the two Solanum studies were chromosomally colocalized, indicating a shared evolutionary history for these QTL, a nonrandom genomic distribution of loci causing sterility, and/or a proclivity of certain genes to be involved in hybrid sterility. We show that comparative mapping data can delimit the probable timing of evolution of detected QTL and discern which sterility loci likely evolved earliest among species.

Genetics and Lineage-Specific Evolution of a Lethal Hybrid Incompatibility Between Drosophila mauritiana and Its Sibling Species

Cattani, M. Victoria; Presgraves, Daven C.
Fonte: Genetics Society of America Publicador: Genetics Society of America
Tipo: Artigo de Revista Científica
Publicado em /04/2009 EN
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The Dobzhansky–Muller model posits that intrinsic postzygotic reproductive isolation—the sterility or lethality of species hybrids—results from the evolution of incompatible epistatic interactions between species: favorable or neutral alleles that become fixed in the genetic background of one species can cause sterility or lethality in the genetic background of another species. The kind of hybrid incompatibility that evolves between two species, however, depends on the particular evolutionary history of the causative substitutions. An allele that is functionally derived in one species can be incompatible with an allele that is functionally derived in the other species (a derived-derived hybrid incompatibility). But an allele that is functionally derived in one species can also be incompatible with an allele that has retained the ancestral state in the other species (a derived-ancestral hybrid incompatibility). The relative abundance of such derived-derived vs. derived-ancestral hybrid incompatibilities is unknown. Here, we characterize the genetics and evolutionary history of a lethal hybrid incompatibility between Drosophila mauritiana and its two sibling species, D. sechellia and D. simulans. We show that a hybrid lethality factor(s) in the pericentric heterochromatin of the D. mauritiana X chromosome...

COGENT (COlorectal cancer GENeTics): an international consortium to study the role of polymorphic variation on the risk of colorectal cancer

Tomlinson, I P M; Dunlop, M; Campbell, H; Zanke, B; Gallinger, S; Hudson, T; Koessler, T; Pharoah, P D; Niittymäkix, I; Tuupanenx, S; Aaltonen, L A; Hemminki, K; Lindblom, A; Försti, A; Sieber, O; Lipton, L; van Wezel, T; Morreau, H; Wijnen, J T; Devile
Fonte: Nature Publishing Group Publicador: Nature Publishing Group
Tipo: Artigo de Revista Científica
EN
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It is now recognised that a part of the inherited risk of colorectal cancer (CRC) can be explained by the co-inheritance of low-penetrance genetic variants. The accumulated experience to date in identifying these variants has served to highlight difficulties in conducting statistically and methodologically rigorous studies and follow-up analyses. The COGENT (COlorectal cancer GENeTics) consortium includes 20 research groups in Europe, Australia, the Americas, China and Japan. The overarching goal of COGENT is to identify and characterise low-penetrance susceptibility variants for CRC through association-based analyses. In this study, we review the rationale for identifying low-penetrance variants for CRC and our proposed strategy for establishing COGENT.

The 1948 International Congress of Genetics in Sweden: People and Politics

Bengtsson, Bengt O.; Tunlid, Anna
Fonte: Genetics Society of America Publicador: Genetics Society of America
Tipo: Artigo de Revista Científica
Publicado em /07/2010 EN
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The International Congresses have played an important role in the history of genetics. The Eighth International Congress, which in 1948 was held in Sweden, celebrated the conclusion of the war against Nazism and many new decisive scientific advances. It also signaled a hardening of the fight against Lysenkoism, which was growing in strength in the Soviet Union. A rare document is available from the Congress—an amateur film made by a young delegate, Nils Nybom. With its help a living description can be given of the scientific and political melees in which the delegates were involved.

A Principled Approach to Deriving Approximate Conditional Sampling Distributions in Population Genetics Models with Recombination

Paul, Joshua S.; Song, Yun S.
Fonte: Genetics Society of America Publicador: Genetics Society of America
Tipo: Artigo de Revista Científica
Publicado em /09/2010 EN
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36.15%
The multilocus conditional sampling distribution (CSD) describes the probability that an additionally sampled DNA sequence is of a certain type, given that a collection of sequences has already been observed. The CSD has a wide range of applications in both computational biology and population genomics analysis, including phasing genotype data into haplotype data, imputing missing data, estimating recombination rates, inferring local ancestry in admixed populations, and importance sampling of coalescent genealogies. Unfortunately, the true CSD under the coalescent with recombination is not known, so approximations, formulated as hidden Markov models, have been proposed in the past. These approximations have led to a number of useful statistical tools, but it is important to recognize that they were not derived from, though were certainly motivated by, principles underlying the coalescent process. The goal of this article is to develop a principled approach to derive improved CSDs directly from the underlying population genetics model. Our approach is based on the diffusion process approximation and the resulting mathematical expressions admit intuitive genealogical interpretations, which we utilize to introduce further approximations and make our method scalable in the number of loci. The general algorithm presented here applies to an arbitrary number of loci and an arbitrary finite-alleles recurrent mutation model. Empirical results are provided to demonstrate that our new CSDs are in general substantially more accurate than previously proposed approximations.

Progress and Promise of Genome-Wide Association Studies for Human Complex Trait Genetics

Stranger, Barbara E.; Stahl, Eli A.; Raj, Towfique
Fonte: Genetics Society of America Publicador: Genetics Society of America
Tipo: Artigo de Revista Científica
Publicado em /02/2011 EN
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Enormous progress in mapping complex traits in humans has been made in the last 5 yr. There has been early success for prevalent diseases with complex phenotypes. These studies have demonstrated clearly that, while complex traits differ in their underlying genetic architectures, for many common disorders the predominant pattern is that of many loci, individually with small effects on phenotype. For some traits, loci of large effect have been identified. For almost all complex traits studied in humans, the sum of the identified genetic effects comprises only a portion, generally less than half, of the estimated trait heritability. A variety of hypotheses have been proposed to explain why this might be the case, including untested rare variants, and gene–gene and gene–environment interaction. Effort is currently being directed toward implementation of novel analytic approaches and testing rare variants for association with complex traits using imputed variants from the publicly available 1000 Genomes Project resequencing data and from direct resequencing of clinical samples. Through integration with annotations and functional genomic data as well as by in vitro and in vivo experimentation, mapping studies continue to characterize functional variants associated with complex traits and address fundamental issues such as epistasis and pleiotropy. This review focuses primarily on the ways in which genome-wide association studies (GWASs) have revolutionized the field of human quantitative genetics.

New Experiments for an Undivided Genetics

Rose, Michael R.; Mueller, Laurence D.; Burke, Molly K.
Fonte: Genetics Society of America Publicador: Genetics Society of America
Tipo: Artigo de Revista Científica
Publicado em /05/2011 EN
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There used to be a broad split within the experimental genetics research community between those who did mechanistic research using homozygous laboratory strains and those who studied patterns of genetic variation in wild populations. The former benefited from the advantage of reproducible experiments, but faced difficulties of interpretation given possible genomic and evolutionary complexities. The latter research approach featured readily interpreted evolutionary and genomic contexts, particularly phylogeny, but was poor at determining functional significance. Such burgeoning experimental strategies as genome-wide analysis of quantitative trait loci, genotype–phenotype associations, and the products of experimental evolution are now fostering a unification of experimental genetic research that strengthens its scientific power.

The Population Genetics of X–Autosome Synthetic Lethals and Steriles

Lachance, Joseph; Johnson, Norman A.; True, John R.
Fonte: Genetics Society of America Publicador: Genetics Society of America
Tipo: Artigo de Revista Científica
Publicado em /11/2011 EN
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Epistatic interactions are widespread, and many of these interactions involve combinations of alleles at different loci that are deleterious when present in the same individual. The average genetic environment of sex-linked genes differs from that of autosomal genes, suggesting that the population genetics of interacting X-linked and autosomal alleles may be complex. Using both analytical theory and computer simulations, we analyzed the evolutionary trajectories and mutation–selection balance conditions for X–autosome synthetic lethals and steriles. Allele frequencies follow a set of fundamental trajectories, and incompatible alleles are able to segregate at much higher frequencies than single-locus expectations. Equilibria exist, and they can involve fixation of either autosomal or X-linked alleles. The exact equilibrium depends on whether synthetic alleles are dominant or recessive and whether fitness effects are seen in males, females, or both sexes. When single-locus fitness effects and synthetic incompatibilities are both present, population dynamics depend on the dominance of alleles and historical contingency (i.e., whether X-linked or autosomal mutations occur first). Recessive synthetic lethality can result in high-frequency X-linked alleles...

Genetics of Ascites Resistance and Tolerance in Chicken: A Random Regression Approach

Kause, Antti; van Dalen, Sacha; Bovenhuis, Henk
Fonte: Genetics Society of America Publicador: Genetics Society of America
Tipo: Artigo de Revista Científica
Publicado em 01/05/2012 EN
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Resistance and tolerance are two complementary mechanisms to reduce the detrimental effects of parasites, pathogens, and production diseases on host performance. Using body weight and ascites data on domesticated chicken Gallus gallus domesticus, we demonstrate the use of random regression animal model and covariance functions to estimate genetic parameters for ascites resistance and tolerance and illustrate the way individual variation in resistance and tolerance induce both genotype re-ranking and changes in variation of host performance along increasing ascites severity. Tolerance to ascites displayed significant genetic variance, with the estimated breeding values of tolerance slope ranging from strongly negative (very sensitive genotype) to weakly negative (less sensitive). Resistance to ascites had heritability of 0.34. Both traits are hence expected to respond to selection. The two complementary defense strategies, tolerance and resistance, were genetically independent. Ascites induced changes to the correlations between ascites resistance and body weight, with the genetic correlations being weak when birds were ascites-free but moderately negative when both healthy and affected birds were present. This likely results because ascites reduces growth...

Notch and the Awesome Power of Genetics

Greenwald, Iva
Fonte: Genetics Society of America Publicador: Genetics Society of America
Tipo: Artigo de Revista Científica
Publicado em /07/2012 EN
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Notch is a receptor that mediates cell–cell interactions in animal development, and aberrations in Notch signal transduction can cause cancer and other human diseases. Here, I describe the major advances in the Notch field from the identification of the first mutant in Drosophila almost a century ago through the elucidation of the unusual mechanism of signal transduction a little over a decade ago. As an essay for the GENETICS Perspectives series, it is my personal and critical commentary as well as an historical account of discovery.

The Genetics of Canine Skull Shape Variation

Schoenebeck, Jeffrey J.; Ostrander, Elaine A.
Fonte: Genetics Society of America Publicador: Genetics Society of America
Tipo: Artigo de Revista Científica
Publicado em /02/2013 EN
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A dog’s craniofacial diversity is the result of continual human intervention in natural selection, a process that began tens of thousands of years ago. To date, we know little of the genetic underpinnings and developmental mechanisms that make dog skulls so morphologically plastic. In this Perspectives, we discuss the origins of dog skull shapes in terms of history and biology and highlight recent advances in understanding the genetics of canine skull shapes. Of particular interest are those molecular genetic changes that are associated with the development of distinct breeds.

Transposing from the Laboratory to the Classroom to Generate Authentic Research Experiences for Undergraduates

Burnette, James M.; Wessler, Susan R.
Fonte: Genetics Society of America Publicador: Genetics Society of America
Tipo: Artigo de Revista Científica
Publicado em /02/2013 EN
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Large lecture classes and standardized laboratory exercises are characteristic of introductory biology courses. Previous research has found that these courses do not adequately convey the process of scientific research and the excitement of discovery. Here we propose a model that provides beginning biology students with an inquiry-based, active learning laboratory experience. The Dynamic Genome course replicates a modern research laboratory focused on eukaryotic transposable elements where beginning undergraduates learn key genetics concepts, experimental design, and molecular biological skills. Here we report on two key features of the course, a didactic module and the capstone original research project. The module is a modified version of a published experiment where students experience how virtual transposable elements from rice (Oryza sativa) are assayed for function in transgenic Arabidopsis thaliana. As part of the module, students analyze the phenotypes and genotypes of transgenic plants to determine the requirements for transposition. After mastering the skills and concepts, students participate in an authentic research project where they use computational analysis and PCR to detect transposable element insertion site polymorphism in a panel of diverse maize strains. As a consequence of their engagement in this course...

Modeling Causality for Pairs of Phenotypes in System Genetics

Neto, Elias Chaibub; Broman, Aimee T.; Keller, Mark P.; Attie, Alan D.; Zhang, Bin; Zhu, Jun; Yandell, Brian S.
Fonte: Genetics Society of America Publicador: Genetics Society of America
Tipo: Artigo de Revista Científica
Publicado em /03/2013 EN
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36.15%
Current efforts in systems genetics have focused on the development of statistical approaches that aim to disentangle causal relationships among molecular phenotypes in segregating populations. Reverse engineering of transcriptional networks plays a key role in the understanding of gene regulation. However, transcriptional regulation is only one possible mechanism, as methylation, phosphorylation, direct protein–protein interaction, transcription factor binding, etc., can also contribute to gene regulation. These additional modes of regulation can be interpreted as unobserved variables in the transcriptional gene network and can potentially affect its reconstruction accuracy. We develop tests of causal direction for a pair of phenotypes that may be embedded in a more complicated but unobserved network by extending Vuong’s selection tests for misspecified models. Our tests provide a significance level, which is unavailable for the widely used AIC and BIC criteria. We evaluate the performance of our tests against the AIC, BIC, and a recently published causality inference test in simulation studies. We compare the precision of causal calls using biologically validated causal relationships extracted from a database of 247 knockout experiments in yeast. Our model selection tests are more precise...

Systems Genetics Implicates Cytoskeletal Genes in Oocyte Control of Cloned Embryo Quality

Cheng, Yong; Gaughan, John; Midic, Uros; Han, Zhiming; Liang, Cheng-Guang; Patel, Bela G.; Latham, Keith E.
Fonte: Genetics Society of America Publicador: Genetics Society of America
Tipo: Artigo de Revista Científica
Publicado em /03/2013 EN
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Cloning by somatic cell nuclear transfer is an important technology, but remains limited due to poor rates of success. Identifying genes supporting clone development would enhance our understanding of basic embryology, improve applications of the technology, support greater understanding of establishing pluripotent stem cells, and provide new insight into clinically important determinants of oocyte quality. For the first time, a systems genetics approach was taken to discover genes contributing to the ability of an oocyte to support early cloned embryo development. This identified a primary locus on mouse chromosome 17 and potential loci on chromosomes 1 and 4. A combination of oocyte transcriptome profiling data, expression correlation analysis, and functional and network analyses yielded a short list of likely candidate genes in two categories. The major category—including two genes with the strongest genetic associations with the traits (Epb4.1l3 and Dlgap1)—encodes proteins associated with the subcortical cytoskeleton and other cytoskeletal elements such as the spindle. The second category encodes chromatin and transcription regulators (Runx1t1, Smchd1, and Chd7). Smchd1 promotes X chromosome inactivation, whereas Chd7 regulates expression of pluripotency genes. Runx1t1 has not been associated with these processes...

The Molecular Genetics of Insecticide Resistance

ffrench-Constant, Richard H.
Fonte: Genetics Society of America Publicador: Genetics Society of America
Tipo: Artigo de Revista Científica
Publicado em /08/2013 EN
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The past 60 years have seen a revolution in our understanding of the molecular genetics of insecticide resistance. While at first the field was split by arguments about the relative importance of mono- vs. polygenic resistance and field- vs. laboratory-based selection, the application of molecular cloning to insecticide targets and to the metabolic enzymes that degrade insecticides before they reach those targets has brought out an exponential growth in our understanding of the mutations involved. Molecular analysis has confirmed the relative importance of single major genes in target-site resistance and has also revealed some interesting surprises about the multi-gene families, such as cytochrome P450s, involved in metabolic resistance. Identification of the mutations involved in resistance has also led to parallel advances in our understanding of the enzymes and receptors involved, often with implications for the role of these receptors in humans. This Review seeks to provide an historical perspective on the impact of molecular biology on our understanding of resistance and to begin to look forward to the likely impact of rapid advances in both sequencing and genome-wide association analysis.