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176 results for “qtl”
Data from: Estimating parent-specific QTL effects through cumulating linked identity-by-state SNP effects in multiparental populations
The emergence of multiparental mapping populations enabled plant geneticists to gain deeper insights into the genetic architecture of major agronomic traits and to map quantitative trait loci (QTLs) controlling the expression of these traits. Although the investigated mapping populations are similar, one open question is whether genotype data should be modelled as identical by state (IBS) or identical by descent (IBD). Whereas IBS simply makes use of raw genotype scores to distinguish alleles, IBD data are derived from parental offspring information. We report on comparing IBS and IBD by applying two multiple regression models on four traits studied in the barley nested association mapping (NAM) population HEB-25. We observed that modelling parent-specific IBD genotypes produced a lower number of significant QTLs with increased prediction abilities compared with modelling IBS genotypes. However, at lower trait heritabilities the IBS model produced higher prediction abilities. We developed a method to estimate multiallelic QTL effects in multiparental populations from simple biallelic IBS data. This method is based on cumulating IBS-derived single-nucleotide polymorphism (SNP) effect estimates in a defined genetic region surrounding a QTL. Comparing the resulting parent-specific QTL effects with those obtained from IBD approaches revealed high accordance that could be confirmed through simulations. The method turned out to be also applicable to a barley multiparent advanced generation inter-cross (MAGIC) population. The 'cumulation method' represents a universal approach to differentiate parent-specific QTL effects in multiparental populations, even if no IBD information is available. In future, the method could further benefit from the availability of much denser SNP maps.
Data from: QTL linkage mapping of wing length in zebra finch using genome-wide single nucleotide polymorphisms markers
Avian wing length is an important trait that covaries with the ecology and migratory behaviour of a species and tends to change rapidly when the conditions are altered. Long-distance migrants typically have longer wings than short-distance migrants and sedentary species, and long-winged species also tend to be more dispersive. Although the substantial heritability of avian wing length is well established, the identification of causal genes has remained elusive. Based on large-scale genotyping of 1404 informative single nucleotide polymorphisms (SNP) in a captive population of 1067 zebra finches, we here show that the within-population variation of relative wing length (h2 = 0.74 ± 0.05) is associated with standing genetic variation in at least six genomic regions (one genome-wide significant and five suggestive). The variance explained by these six quantitative trait loci (QTL) sums to 36.8% of the phenotypic variance (half of the additive genetic variance), although this likely is an overestimate attributable to the Beavis effect. As avian wing length is primarily determined by the length of the primary feathers, we then searched for candidate genes that are related to feather growth. Interestingly, all of the QTL signals co-locate with Wnt growth factors and closely interacting genes (Wnt3a, Wnt5a, Wnt6, Wnt7a, Wnt9a, RhoU and RhoV). Our findings therefore suggest that standing genetic variation in the Wnt genes might be linked to avian wing morphology, although there are many other genes that also fall within the confidence regions.
Data from: Extreme QTL mapping of germination speed in Arabidopsis thaliana
Seed germination is a key life history transition for annual plants and partly determines lifetime performance and fitness. Germination speed, the elapsed time for a nondormant seed to germinate, is a poorly understood trait important for plants' competitiveness and fitness in fluctuating environments. Germination speed varied by 30% among 18 Arabidopsis thaliana populations measured, and exhibited weak negative correlation with flowering time and seed weight, with significant genotype effect (P < 0.005). To dissect the genetic architecture of germination speed, we developed the extreme QTL (X-QTL) mapping method in A. thaliana. The method has been shown in yeast to increase QTL mapping power by integrating selective screening and bulk-segregant analysis in a very large mapping population. By pooled genotyping of top 5% of rapid germinants from ~100 000 F3 individuals, three X-QTL regions were identified on chromosomes 1, 3 and 4. All regions were confirmed as QTL regions by sequencing 192 rapid germinants from an independent F3 selection experiment. Positional overlaps were found between X-QTLs and previously identified seed, life history and fitness QTLs. Our method provides a rapid mapping platform in A. thaliana with potentially greater power. One can also relate identified X-QTLs to the A. thaliana physical map, facilitating candidate gene identification.
Data from: Identification of the submergence tolerance QTL come quick drowning1 (CQD1) in Arabidopsis thaliana
Global climate change is predicted to increase water precipitation fluctuations and lead to localized prolonged floods in agricultural fields and natural plant communities. Thus, understanding the genetic basis of submergence tolerance is crucial in order to improve plant survival under these conditions. In this study, we performed a quantitative trait locus (QTL) analysis in Arabidopsis to identify novel candidate genes for increased submergence tolerance by using Kas-1 and Col (gl1) parental accessions and their derived recombinant inbred lines (RILs). We measured survival after submergence in dark for a 13-day period and used median lethal time, LT50 values for the QTL analysis. A major QTL, the Come Quick, Drowning (CQD1) locus, was detected in 2 independent experiments on the lower arm of chromosome 5 involved in higher submergence tolerance in the parental accession Kas-1. For fine-mapping, we then constructed near isogenic lines (NILs) by backcrossing the CQD1 QTL region. We also analyzed QTL regions related to size, leaf number, flowering, or survival in darkness and none of the QTL related to these traits overlapped with CQD1. The submergence tolerance QTL, CQD1, region detected in this study includes genes that have potential to be novel candidates effecting submergence tolerance such as trehalose-6-phosphate phosphatase and respiratory burst oxidase protein D. Gene expression and functional analysis for these genes under submergence would reveal the significance of these novel candidates and provide new perspectives for understanding genetic basis of submergence tolerance.
Data from: Genetic dissection of a genomic region with pleiotropic effects on domestication traits in maize reveals multiple linked QTL
The domesticated crop maize and its wild progenitor, teosinte, have been used in numerous experiments to investigate the nature of divergent morphologies. This study examines a poorly understood region on the fifth chromosome of maize associated with a number of traits under selection during domestication using a QTL mapping population specific to the fifth chromosome. In contrast with other major domestication loci in maize where large effect, highly pleiotropic, single genes are responsible for phenotypic effects, our study found the region on chromosome five fractionates into multiple QTL regions, none with singularly large effects. The smallest 1.5 LOD support interval for a QTL contained 54 genes, one of which was a MADS MIKCC transcription factor, a family of proteins implicated in many developmental programs. We also used simulated trait datasets to investigate the power of our mapping population to identify QTL for which there is a single underlying causal gene. This analysis showed that while QTL for traits controlled by single genes can be accurately mapped, our population design can detect no more than ~4.5 QTL per trait even when there are 100 causal genes. Thus when a trait is controlled by 5 or more genes in the simulated data, the number of detected QTL can represent a simplification of the underlying causative factors. Our results show how a QTL region with effects on several domestication traits may be due to multiple linked QTL of small effect as opposed to a single gene with large and pleiotropic effects.
Data from: Identification of multiple QTL hotspots in sockeye salmon (Oncorhynchus nerka) using genotyping-by-sequencing and a dense linkage map
Understanding the genetic architecture of phenotypic traits can provide important information about the mechanisms and genomic regions involved in local adaptation and speciation. Here, we used genotyping-by-sequencing and a combination of previously published and newly generated data to construct sex-specific linkage maps for sockeye salmon (Oncorhynchus nerka). We then used the denser female linkage map to conduct quantitative trait locus (QTL) analysis for 4 phenotypic traits in 3 families. The female linkage map consisted of 6322 loci distributed across 29 linkage groups and was 4082 cM long, and the male map contained 2179 loci found on 28 linkage groups and was 2291 cM long. We found 26 QTL: 6 for thermotolerance, 5 for length, 9 for weight, and 6 for condition factor. QTL were distributed nonrandomly across the genome and were often found in hotspots containing multiple QTL for a variety of phenotypic traits. These hotspots may represent adaptively important regions and are excellent candidates for future research. Comparing our results with studies in other salmonids revealed several regions with overlapping QTL for the same phenotypic trait, indicating these regions may be adaptively important across multiple species. Altogether, our study demonstrates the utility of genomic data for investigating the genetic basis of important phenotypic traits. Additionally, the linkage map created here will enable future research on the genetic basis of phenotypic traits in salmon.
Data from: QTL and quantitative genetic analysis of beak morphology reveals patterns of standing genetic variation in an Estrildid finch
The intra- and interspecific diversity of avian beak morphologies is one of the most compelling examples for the power of natural selection acting on a morphological trait. The development and diversification of the beak has also become a textbook example for evolutionary developmental biology, and variation in expression levels of several genes is known to causally affect beak shape. However, until now no genomic polymorphisms have been identified that are related to beak morphology in birds. QTL mapping does reveal the location of causal polymorphisms, albeit with poor spatial resolution. Here we estimate heritability and genetic correlations for beak length, depth and width and perform a QTL linkage analysis for these traits based on 1,404 informative single nucleotide polymorphisms genotyped in a four generation pedigree of 992 captive zebra finches (Taeniopygia guttata). Beak size, relative to body size, was sexually dimorphic (larger in males). Heritability estimates ranged from 0.47 for beak length to 0.74 for beak width. QTL mapping revealed four to five regions of significant or suggestive genome-wide linkage for each of the three beak dimensions (nine different regions in total). Eight out of eleven genes known to influence beak morphology are located in these nine peak regions. Five QTL do not cover known candidates demonstrating that yet unknown genes or regulatory elements may influence beak morphology in the zebra finch.
Data from: High fidelity detection of crop biomass QTL from low-cost imaging in the field
Field-based, rapid, and non-destructive techniques for assessing plant productivity are needed to accelerate the discovery of genotype-to-phenotype relationships in next-generation biomass grass crops. The use of hemispherical imaging and light attenuation modeling was evaluated against destructive harvest measures with respect to their ability to accurately capture phenotypic and genotypic relationships in a field-grown grass crop. Plant area index (PAI) estimated from below-canopy hemispherical images, as well as a suite of thirteen traits assessed by manual destructive harvests, were measured in a Setaria recombinant inbred line mapping population segregating for aboveground productivity and architecture. A significant correlation was observed between PAI and biomass production across the population at maturity (r2 = 0.60), as well as for select diverse genotypes sampled repeatedly over the growing season (r2 = 0.79). Twenty-seven quantitative trait loci (QTL) were detected for manually collected traits associated with biomass production. Of these, twenty-one were found in four clusters of co-localized QTL. Analysis of image-based estimates of PAI successfully identified all four QTL hotspots for biomass production. QTL for PAI had greater overlap with those detected for traits associated with biomass production than with those for plant architecture and biomass partitioning. Hemispherical imaging is an affordable and scalable method, which demonstrates how high-throughput phenotyping can identify QTL related to biomass production of field trials in place of destructive harvests that are labor, time, and material intensive.
Petal size in rapeseed: novel QTL and candidate genes detected through genome-wide association study and transcriptome comparison
<p>Petal size determines the value of ornamental plants, and thus their economic worth. However, the molecular mechanisms controlling petal size remain unclear in most non-model species. To identify quantitative trait loci and candidate genes regulating petal size in rapeseed (<i>Brassica napus</i>), we performed a genome-wide association study (GWAS) using data from 588 accessions over three consecutive years. We detected 17 significant single nucleotide polymorphisms (SNPs) associated with petal size, with the most significant SNPs located on chromosomes A05 and C06. A combination of GWAS and transcriptomic sequencing based on two accessions with extreme differences in petal size identified 11 differentially expressed genes (DEGs) that may control petal size variation in rapeseed. In particular, <i>BnaA05</i><i>.</i><i>RAP2.2</i> homologous to <i>RAP2.2</i> in rapeseed may be a critical gene negatively influencing petal size through the ethylene signaling pathway. In addition, a comparison of petal epidermal cells indicated that petal size differences between the two extreme accessions were determined mainly by cell number differences. Finally, we propose a preliminary model for the control of petal size in rapeseed. Our results provide insights into the genetic mechanisms regulating petal size, and also lay the foundation for a better understanding of petal development in plants.</p>
Genome-wide association analysis reveals QTL and candidate mutations involved in white spotting in cattle
<p><b>Background</b></p> <p>White spotting of the coat is a characteristic trait of various domestic species including cattle and other mammals. It is a hallmark of Holstein-Friesian cattle, and several previous studies have detected genetic loci with major effects for white spotting in animals with Holstein-Friesian ancestry. Here, our aim was to better understand the underlying genetic and molecular mechanisms of white spotting, by conducting the largest mapping study for this trait in cattle, to date.</p> <p><b>Results</b></p> <p>Using imputed whole-genome sequence data, we conducted a genome-wide association analysis in 2,973 mixed-breed cows and bulls. Highly significant quantitative trait loci (QTL) were found on chromosomes 6 and 22, highlighting the well-established coat color genes <i>KIT</i> and <i>MITF</i> as likely responsible for these effects. These results are in broad agreement with previous studies, although we also report a third significant QTL on chromosome 2 that appears to be novel. This signal maps immediately adjacent to the <i>PAX3</i> gene, which encodes a known transcription factor that controls <i>MITF </i>expression and is the causal locus for white spotting in horses. More detailed examination of these loci revealed a candidate causal mutation in <i>PAX3</i> (p.Thr424Met), and another candidate mutation (rs209784468) within a conserved element in intron 2 of <i>MITF</i> transcripts expressed in the skin. These analyses also revealed a mechanistic ambiguity at the chromosome 6 locus, where highly dispersed association signals suggested multiple or multiallelic QTL involving <i>KIT </i>and/or other genes in this region.</p> <p><b>Conclusions</b></p> <p>Our findings extend those of previous studies that reported <i>KIT</i> as a likely causal gene for white spotting, and report novel associations between candidate causal mutations in both the <i>MITF</i> and <i>PAX3</i> genes. The sizes of the effects of these QTL are substantial, and could be used to select animals with darker, or conversely whiter, coats depending on the desired characteristics.</p>
Data from: X-chromosome meiotic drive in Drosophila simulans: a QTL approach reveals the complex polygenic determinism of Paris drive suppression
Meiotic drivers are selfish genetic elements that promote their own transmission into the gametes, which results in intragenomic conflicts. In the Paris sex-ratio system of Drosophila simulans, drivers located on the X chromosome prevent the segregation of the heterochromatic Y chromosome during meiosis II, and hence the production of Y-bearing sperm. The resulting sex-ratio bias strongly impacts population dynamics and evolution. Natural selection, which tends to restore an equal sex ratio, favors the emergence of resistant Y chromosomes and autosomal suppressors. This is the case in the Paris sex-ratio system where the drivers became cryptic in most of the natural populations of D. simulans. Here, we used a Quantitative Trait Locus (QTL) mapping approach based on the analysis of 152 highly recombinant inbred lines (RILs) to investigate the genetic determinism of autosomal suppression. The RILs were derived from an advanced intercross between two parental lines, one showing complete autosomal suppression while the other one was sensitive to drive. The confrontation of RIL autosomes with a reference XSR chromosome allowed us to identify two QTLs on chromosome 2 and three on chromosome 3, with strong epistatic interactions. Our findings highlight the multiplicity of actors involved in this intragenomic battle over the sex ratio.
Data from: Mapping QTL contributing to variation in posterior lobe morphology between strains of Drosophila melanogaster
Closely-related, and otherwise morphologically similar insect species frequently show striking divergence in the shape and/or size of male genital structures, a phenomenon thought to be driven by sexual selection. Comparative interspecific studies can help elucidate the evolutionary forces acting on genital structures to drive this rapid differentiation. However, genetic dissection of sexual trait divergence between species is frequently hampered by the difficulty generating interspecific recombinants. Intraspecific variation can be leveraged to investigate the genetics of rapidly-evolving sexual traits, and here we carry out a genetic analysis of variation in the posterior lobe within D. melanogaster. The lobe is a male-specific process emerging from the genital arch of D. melanogaster and three closely-related species, is essential for copulation, and shows radical divergence in form across species. There is also abundant variation within species in the shape and size of the lobe, and while this variation is considerably more subtle than that seen among species, it nonetheless provides the raw material for QTL mapping. We created an advanced intercross population from a pair of phenotypically-different inbred strains, and after phenotyping and genotyping-by-sequencing the recombinants, mapped several QTL contributing to various measures of lobe morphology. The additional generations of crossing over in our mapping population led to QTL intervals that are smaller than is typical for an F2 mapping design. The intervals we map overlap with a pair of lobe QTL we previously identified in an independent mapping cross, potentially suggesting a level of shared genetic control of trait variation. Our QTL additionally implicate a suite of genes that have been shown to contribute to the development of the posterior lobe. These loci are strong candidates to harbor naturally-segregating sites contributing to phenotypic variation within D. melanogaster, and may also be those contributing to divergence in lobe morphology between species.
Data from: Estimating parent-specific QTL effects through cumulating linked identity-by-state SNP effects in multiparental populations
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Data from: Mapping and validation of a major QTL affecting resistance to pancreas disease (salmonid alphavirus) in Atlantic salmon (Salmo salar)
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Data from: A dense linkage map of Lake Victoria cichlids improved the Pundamilia genome assembly and revealed a major QTL for sex-determination
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Data from: X-chromosome meiotic drive in Drosophila simulans: a QTL approach reveals the complex polygenic determinism of Paris drive suppression
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Data from: QTL linkage mapping of wing length in zebra finch using genome-wide single nucleotide polymorphisms markers
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Data from: Identification of multiple QTL hotspots in sockeye salmon (Oncorhynchus nerka) using genotyping-by-sequencing and a dense linkage map
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Data from: QTL analysis of behavior in nine-spined sticklebacks (Pungitius pungitius)
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Data from: Genetic dissection of a genomic region with pleiotropic effects on domestication traits in maize reveals multiple linked QTL
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