Search bioRxiv⌕ Search

SEARCH · Search bioRxiv

Results for “Genetics”

Search indexed bioRxiv preprints in genomics, neuroscience, cell biology and bioinformatics. Read source abstracts and check manuscript versions; preprints are not peer reviewed.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,711 records · Page 95Linked to original sources

Genome-wide association mapping and systems-level analysis reveal genetic architecture and physiological mechanisms linked with tolerance to flooding during germination in rice

Rice is the staple food of more than half of the worlds population; yet, it faces numerous challenges to meet the rising food demands and worsening climates. An urgent global imperative is to address imminent food shortages through intensive and sustainable agri-food systems and steady genetic gains. Intensification of rice production through direct-seeded rice (DSR) has been progressively practiced but is hindered by poor germination of existing high-yielding varieties in flooded soils. Identifying donors of anaerobic germination (AG) tolerance in rice will expedite the development of varieties suitable for DSR and will lead to enhanced and sustained agricultural productivity. This study aims to dissect the genetic architecture and physiological mechanisms of AG tolerance using systems biology and omics approaches. A Rice Diversity Panel (343 accessions) consisting of 5 subpopulations was screened for AG tolerance under greenhouse conditions, mapped through genome-wide association study (GWAS), and profiled for metabolites. Analyses revealed that most of the AG-tolerant varieties are japonicas with few indicas) and aus. Tolerant japonicas employed better root growth or rapid shoot extension, while tolerant indicas exhibited only the latter. A total of 51 significant GWAS peaks were detected across the genome, some of which were co-localized with known quantitative trait loci while others were novel, more so tolerance was found to involve different genetic controls across subpopulations. AG stress causes distinct biochemical signatures for tolerant genotypes and the profiles contrast among subpopulations implicating divergent metabolic adjustments, including shifts in sugars, intermediates, amino acids, antioxidants, and hormones. This study provides a systems-level approach for underpinning physiological mechanisms of AG tolerance; elucidating phenotypic heterogeneity, genetic architecture, transcriptomic networks, and metabolic landscapes from a genome-wide perspective. ONE SENTENCE SUMMARYThe integration of GWA mapping, gene network analysis and, non-targeted metabolite profiling elucidates genetic architecture and physiological mechanisms of tolerance to germination and early seedling growth under anaerobic conditions in rice.

plant biology↗

Genetic diversity and population structure of cowpea accessions from Togo using SSR Markers

Cowpea [Vigna unguiculata (L.) Walp.] is a crop with significant agronomic and nutritional potential. I is very appreciate by local people. It is the third food habit in Togo after maize and rice. However, several accessions of cowpea cultivated in Togo are now prone to extinction, creating a risk of genetic erosion. It is therefore urgent to assess the genetic diversity of accessions in order to set up a good conservation program. To achieve this, genetic diversity and phylogenetic relationships among 70 accessions of cowpea collected in the five (5) administrative regions of Togo were assessed using Simple Sequence Repeat (SSR) molecular markers. Twenty-eight out of the thirty-two (32) primer pairs screened for polymorphism were polymorphic, and a total of 164 alleles were detected for the 28 loci with an average of 5.82 alleles per locus. Polymorphic Information Content (PIC) values ranged from 0.18 to 0.895, with an average value of 0.67. Population structure analysis using model-based revealed that the cowpea germplasm was grouped into two subpopulations. The analysis of molecular variance (AMOVA) revealed that 85% of genetic variation existed among individuals within regions. The fixation index (Fst) value, which was 0.018, was low, indicating relatively low population differentiation. The Togolese cowpea germplasm collection was grouped into four groups independently of theirs origins. This study provides a foundation for a Togolese cowpea germplasm conservation program and can serve for the selection of parental material for further studies aimed at the genetic improvement of local germplasm.

molecular biology↗

Crossing design shapes patterns of genetic variation in synthetic recombinant populations of Saccharomyces cerevisiae

"Synthetic recombinant" populations have emerged as a useful tool for dissecting the genetics of complex traits. They can be used to derive inbred lines for fine QTL mapping, or the populations themselves can be sampled for experimental evolution. In latter application, investigators generally value maximizing genetic variation in constructed populations. This is because in evolution experiments initiated from such populations, adaptation is primarily fueled by standing genetic variation. Despite this reality, little has been done to systematically evaluate how different methods of constructing synthetic populations shape initial patterns of variation. Here we seek to address this issue by comparing outcomes in synthetic recombinant Saccharomyces cerevisiae populations created using one of two strategies: pairwise crossing of isogenic strains or simple mixing of strains in equal proportion. We also explore the impact of the varying the number of parental strains. We find that more genetic variation is initially present and maintained when population construction includes a round of pairwise crossing. As perhaps expected, we also observe that increasing the number of parental strains typically increases genetic diversity. In summary, we suggest that when constructing populations for use in evolution experiments, simply mixing founder strains in equal proportion may limit the adaptive potential.

genomics↗

Predicting Composition of Genetic Circuits with Resource Competition: Demand and Sensitivity

The design of genetic circuits typically relies on characterization of constituent modules in isolation to predict the behavior of modules composition. However, it has been shown that the behavior of a genetic module changes when other modules are in the cell due to competition for shared resources. In order to engineer multi-module circuits that behave as intended, it is thus necessary to predict changes in the behavior of a genetic module when other modules load cellular resources. Here, we introduce two characteristics of circuit modules: the demand for cellular resources and the sensitivity to resource loading. When both are known for every genetic module in a circuit library, they can be used to predict any modules behavior upon addition of any other module to the cell. We develop an experimental approach to measure both characteristics for any circuit module using a resource sensor module. Using the measured resource demand and sensitivity for each module in a library, the outputs of the modules can be accurately predicted when they are inserted in the cell in arbitrary combinations. These resource competition characteristics may be used to inform the design of genetic circuits that perform as predicted despite resource competition.

synthetic biology↗

A Biologically Interpretable Graph Convolutional Network to Link Genetic Risk Pathways and Neuroimaging Phenotypes of Disease

AO_SCPLOWBSTRACTC_SCPLOWWe propose a novel end-to-end framework for whole-brain and whole-genome imaging-genetics. Our genetics network uses hierarchical graph convolution and pooling operations to embed subject-level data onto a low-dimensional latent space. The hierarchical network implicitly tracks the convergence of genetic risk across well-established biological pathways, while an attention mechanism automatically identifies the salient edges of this network at the subject level. In parallel, our imaging network projects multimodal data onto a set of latent embeddings. For interpretability, we implement a Bayesian feature selection strategy to extract the discriminative imaging biomarkers; these feature weights are optimized alongside the other model parameters. We couple the imaging and genetic embeddings with a predictor network, to ensure that the learned representations are linked to phenotype. We evaluate our framework on a schizophrenia dataset that includes two functional MRI paradigms and gene scores derived from Single Nucleotide Polymorphism data. Using repeated 10-fold cross-validation, we show that our imaging-genetics fusion achieves the better classification performance than state-of-the-art baselines. In an exploratory analysis, we further show that the biomarkers identified by our model are reproducible and closely associated with deficits in schizophrenia.

bioinformatics↗

A marginal habitat, but not a sink: Ecological genetics reveal a diversification hotspot for marine invertebrates in the brackish Baltic Sea

AimEnvironmental gradients have emerged as important barriers structuring populations and species distributions. We set out to test whether a strong salinity gradient from marine to brackish, represented in a marginal northern European sea, should be considered a diversification hotspot or a population sink, and to identify life history traits that correlate with either evolutionary trajectory. LocationThe Baltic Sea, the North Sea and their transition zone. MethodsWe accumulated mitochondrial cytochrome oxidase subunit 1 sequence data and data on the distribution, salinity tolerance and life history for 28 species belonging to the Cnidaria, Crustacea, Echinodermata, Mollusca, Polychaeta and Gastrotricha, including seven non-native species. We calculated measures of genetic diversity and differentiation across the environmental gradient, coalescent times and migration rates between North and Baltic Sea populations, and analysed correlations between genetic and life history data. ResultsThe majority of investigated species is either genetically differentiated and/or is adapted to the lower salinity conditions of the Baltic Sea. Moreover, the species exhibiting population structure have a range of patterns of genetic diversity in comparison to the North Sea, from lower in the Baltic Sea to higher in the Baltic Sea, or equally diverse in North and Baltic Sea. Main conclusionsOur results indicate that the Baltic Sea should be considered a diversification hotspot: The diversity of genetic patterns points towards independent trajectories in the Baltic compared to the North Sea. At the same time, we found limited evidence for the traditional scenario of the Baltic Sea as a population sink with lower diversity and strong gene flow. The North Sea - Baltic Sea region provides a unique setting to study evolutionary adaptation during colonization processes at different stages by jointly considering native and non-native species.

evolutionary biology↗

The contribution of genetic and environmental effects to Bergmanns rule and Allens rule in house mice

Distinguishing between genetic, environmental, and genotype-by-environment effects is central to understanding geographic variation in phenotypic clines. Two of the best-documented phenotypic clines are Bergmanns rule and Allens rule, which describe larger body sizes and shortened extremities in colder climates, respectively. Although numerous studies have found inter- and intraspecific evidence for both ecogeographic patterns, we still have a poor understanding of the extent to which these patterns are driven by genetics, environment, or both. Here, we measured the genetic and environmental contributions to Bergmanns rule and Allens rule across introduced populations of house mice (Mus musculus domesticus) in the Americas. First, we documented clines for body mass, tail length, and ear length in natural populations, and found that these conform to both Bergmanns rule and Allens rule. We then raised descendants of wild-caught mice in the lab and showed that these differences persisted in a common environment and are heritable, indicating that they have a genetic basis. Finally, using a full-sib design, we reared mice under warm and cold conditions. We found very little plasticity associated with body size, suggesting that Bergmanns rule has been shaped by strong directional selection in house mice. However, extremities showed considerable plasticity, as both tails and ears grew shorter in cold environments. These results indicate that adaptive phenotypic plasticity as well as genetic changes underlie major patterns of clinal variation in house mice and likely facilitated their rapid expansion into new environments across the Americas.

evolutionary biology↗

Sex-Specific Plasticity Explains Genetic Variation in Sexual Size Dimorphism in Drosophila

The difference in body size between females and males, or sexual size dimorphism (SSD), is almost ubiquitous, and yet we have a remarkably poor understanding of the developmental-genetic mechanisms that generate it. Such an understanding is important if we are to distinguish between the many theoretical models of SSD evolution. One such model is the condition dependence hypothesis, which proposes that the body size of the larger sex is also more environmentally sensitive, a phenomenon called sex-specific plasticity (SSP). Because SSP generates differences in female and male body size, selection on plasticity may underlie the evolution of sexual size dimorphism. To test this hypothesis, however, we need to know the genetic architecture of both SSD and SSP, which is challenging because both are characteristics of populations not individuals. Here, we overcome this challenge by using isogenic lineages of Drosophila to measure both SSD and SSP for a genotype. We demonstrate extensive genetic variation for SSD among genotypes that is tightly correlated with variation in SSP, indicating that the same developmental-genetic mechanisms regulate both phenomena. These data support the condition dependence hypothesis and suggest that the observed SSD is a consequence of selection on the developmental-genetic mechanisms that regulate SSP.

evolutionary biology↗

Introgression of type-IV glandular trichomes from Solanum galapagense to cultivated tomato reveals genetic complexity for the development of acylsugar-based insect resistance

Glandular trichomes are involved in the production of food- and medicine-relevant chemicals in plants, besides being associated with pest resistance. In some wild Solanum species closely related to the cultivated tomato (S. lycopersicum), the presence of type-IV glandular trichomes leads to the production of high levels of insecticide acylsugars (AS). Conversely, low AS production observed in the cultivated tomato is attributed to its incapacity to develop type-IV trichomes in adult organs. Therefore, we hypothesized that cultivated tomatoes engineered to harbor type-IV trichomes on the leaves of mature plants can be pest resistant. We introgressed into the tomato cultivar Micro-Tom (MT) the capability of S. galapagense to maintain the development of type-IV trichomes throughout all plant stages, thus creating a line named "Galapagos enhanced trichomes" (MT-Get). Mapping-by-sequencing of MT-Get revealed that five chromosomal regions of S. galapagense were present in MT-Get. Further mapping reveled that S. galapagense alleles on chromosomes 1, 2 and 3 are sufficient for the presence of type-IV trichomes, but in lower densities. GC-MS, LC-MS, and gene expression analyses demonstrated that the increased density of type-IV trichomes was not accompanied by high AS production and exudation in MT-Get. Moreover, MT-Get did not differ from MT in its susceptibility to whitefly (Bemisia tabaci). Our findings demonstrates that type-IV glandular trichome development along with AS production and exudation are partially uncoupled at the genetic level. The MT-Get genotype represents a valuable resource for further studies involving the biochemical manipulation of type-IV trichome content through either genetic introgression or transgenic approaches. Significance StatementThis work identified loci in the tomato genome that control the heterochronic development of type-IV glandular trichomes and uncoupled the genetic control of this type of trichome ontogeny from acylsugar biosynthesis and accumulation, revealing a higher than anticipated genetic complexity of acylsugar-based insect resistance. The findings reported herein will contribute to further dissect the genetics of trichome development in tomato as well as to introgress broad and durable insect resistance in tomato and other Solanaceae.

plant biology↗

Genetic diversity in chimpanzee transcriptomics does not represent wild populations

Chimpanzees (Pan troglodytes) are a genetically diverse species, consisting of 4 highly distinct subspecies. As humans closest living relative they have been a key model organism in the study of human evolution, and comparisons of human and chimpanzee transcriptomes have been widely used to characterise differences in gene expression levels that could underlie the phenotypic differences between the two species. However, the subspecies from which these transcriptomic datasets have been derived is not recorded in metadata available in the public NCBI Sequence Read Archive (SRA). Furthermore, labelling of RNA-seq samples is for the most part inconsistent across studies, and the true number of individuals from whom transcriptomic data is available is difficult to ascertain. Thus we have evaluated genetic diversity at the subspecies and individual level in 486 public RNA-seq samples available in the SRA, spanning the vast majority of public chimpanzee transcriptomic data. Using multiple population genetics approaches we find that nearly all samples (96.6%) have some degree of Western chimpanzee ancestry. At the individual donor level, we identify multiple samples that have been repeatedly analysed across different studies, and identify a total of 135 genetically distinct individuals within our data, a number that falls to 89 when we exclude likely first and second-degree relatives. Altogether, our results show that current transcriptomic data from chimpanzees is capturing low levels of genetic diversity relative to what exists in wild chimpanzee populations. These findings provide important context to current comparative transcriptomics research involving chimpanzees.

genomics↗

Identification of genetic markers and wood properties that predict wood biorefinery potential in aspen bioenergy feedstock (Populus tremula).

BackgroundWood represents the majority of the biomass on land and constitutes a renewable source of biofuels and other bioproducts. However, wood is recalcitrant to bioconversion, raising a need for feedstock improvement in production of, for instance, biofuels. We investigated the properties of wood that affect bioconversion, as well as the underlying genetics, to help identify superior tree feedstocks for biorefining. ResultsWe recorded 65 wood-related and growth traits in a population of 113 natural aspen genotypes from Sweden. These traits included three growth and field performance traits, 20 traits for wood chemical composition, 17 traits for wood anatomy and structure, and 25 wood saccharification traits as indicators of bioconversion potential. Glucose release after saccharification with acidic pretreatment correlated positively with tree stem height and diameter and the carbohydrate content of the wood, and negatively with the content of lignin and the hemicellulose sugar units. Most of these traits displayed extensive natural variation within the aspen population and high broad-sense heritability, supporting their potential in genetic improvement of feedstocks towards improved bioconversion. Finally, a genome wide association study (GWAS) revealed 13 genetic loci for saccharification yield (on a whole tree biomass basis), with six of them intersecting with associations for either height or stem diameter of the trees. ConclusionsThe simple growth traits of stem height and diameter were identified as good predictors of wood saccharification yield in aspen trees. GWAS elucidated the underlying genetics, revealing putative genetic markers for bioconversion of bioenergy tree feedstocks.

plant biology↗

Genetic slippage after sex maintains diversity for parasite resistance in a natural host population

Although parasite-mediated selection is thought to be a major driver of host evolution, its influence on genetic variation for parasite resistance is not yet well understood. We monitored a large population of the planktonic crustacean Daphnia magna over eight years, as it underwent yearly epidemics of the bacterial pathogen Pasteuria ramosa. We observed a cyclical pattern of resistance evolution: resistant phenotypes increased in frequency throughout the epidemics, but susceptibility was restored each spring when hosts hatched from sexual resting stages, a phenomenon described as genetic slippage in response to sex. Collecting and hatching D. magna resting stages across multiple seasons showed that largely resistant host populations can produce susceptible offspring through recombination. Resting stages produced throughout the planktonic season accurately represent the hatching population cohort of the following spring. A genetic model of resistance developed for this host-parasite system, based on multiple loci and strong epistasis, is in partial agreement with these findings. Our results reveal that, despite strong selection for resistance in a natural host population, genetic slippage after sexual reproduction has the potential to maintain genetic diversity of host resistance.

evolutionary biology↗

Limitations of lymphoblastoid cell lines for establishing genetic reference datasets in the immunoglobulin loci

Lymphoblastoid cell lines (LCLs) have been critical to establishing genetic resources for biomedical science. They have been used extensively to study human genetic diversity, genome function, and inform the development of tools and methodologies for augmenting disease genetics research. While the validity of variant callsets from LCLs has been demonstrated for most of the genome, previous work has shown that DNA extracted from LCLs is modified by V(D)J recombination within the immunoglobulin (IG) loci, regions that harbor antibody genes critical to immune system function. However, the impacts of V(D)J on data generated from LCLs has not been extensively investigated. In this study, we used LCL-derived short read sequencing data from the 1000 Genomes Project (n=2,504) to identify signatures of V(D)J recombination. Our analyses revealed sample-level impacts of V(D)J recombination that varied depending on the degree of inferred monoclonality. We showed that V(D)J associated somatic deletions impacted genotyping accuracy, leading to adulterated population-level estimates of allele frequency and linkage disequilibrium. These findings illuminate limitations of using LCLs for building genetic resources in the IG loci, with implications for interpreting previous disease association studies in these regions. Author summaryLymphoblastoid cell lines (LCLs) are cells that have been manipulated to proliferate indefinitely in order to provide a replenishable source of DNA. However, because these cell lines are derived from B cells which have undergone V(D)J recombination they contain somatic deletions within regions of the genome that encode antibody genes. Although several large collaborative projects have utilized DNA from LCLs to generate invaluable genomic resources for the scientific community, the negative impacts of cell line artifacts in these regions of the genome have not been fully appreciated. In this study, we used newly released sequencing data from a large collection of LCLs to determine that the non-inherited artificial deletions within the antibody gene loci can have detrimental effects on downstream genetic analyses.

genomics↗

Phenotypic plasticity and genetic control in colorectal cancer evolution

Cancer evolution is driven by natural selection acting upon phenotypic trait variation. However, the extent to which phenotypic variation within a tumour is a consequence of intra-tumour genetic heterogeneity remains undetermined. Here we show that colorectal cancer cells frequently have highly plastic phenotypic traits in vivo in patient tumours. We measured the degree to which trait variation reflects genetic ancestry by quantifying the phylogenetic signal of gene expression across 297 samples with multi-region paired whole genome and transcriptome sequencing collected from 27 primary colorectal cancers. Within-tumour phylogenetic signal for genes and pathways was detected only infrequently, suggesting that the majority of intra-tumour variation in gene expression programmes was not strongly heritable. Expression quantitative trait loci analyses (eQTL) identified a small number of putative mechanisms of genetic control of gene expression due to the cis-acting coding, non-coding and structural genetic alteration, but most gene expression variation was not explained by our genetic analysis. Leveraging matched chromatin-accessibility sequencing data, enhancer mutations with cis regulatory effects on gene expression were associated with a change in chromatin accessibility, indicating that non-coding variation can have phenotypic consequence through modulation of the 3D architecture of the genome. This study maps the evolution of transcriptional variation during cancer evolution, highlighting that intra-tumour phenotypic plasticity is pervasive in colorectal malignancies, and may play key roles in further tumour evolution, from metastasis to therapy resistance.

cancer biology↗

Modeling the C. elegans Germline Stem Cell Genetic Network using Automated Reasoning

Computational methods and tools are a powerful complementary approach to experimental work for studying regulatory interactions in living cells and systems. We demonstrate the use of formal reasoning methods as applied to the Caenorhabditis elegans germ line, which is an accessible model system for stem cell research. The dynamics of the underlying genetic networks and their potential regulatory interactions are key for understanding mechanisms that control cellular decision-making between stem cells and differentiation. We model the "stem cell fate" versus entry into the "meiotic development" pathway decision circuit in the young adult germ line based on an extensive study of published experimental data and known/hypothesized genetic interactions. We apply a formal reasoning framework to derive predictive networks for control of differentiation. Using this approach we simultaneously specify many possible scenarios and experiments together with potential genetic interactions, and synthesize genetic networks consistent with all encoded experimental observations. In silico analysis of knock-down and overexpression experiments within our model recapitulate published phenotypes of mutant animals and can be applied to make predictions on cellular decision-making. This work lays a foundation for developing realistic whole tissue models of the C. elegans germ line where each cell in the model will execute a synthesized genetic network.

systems biology↗

Multi view based imaging genetics analysis on Parkinson disease

Longitudinal studies integrating imaging and genetic data have recently become widespread among bioinformatics researchers. Combining such heterogeneous data allows a better understanding of complex diseases origins and causes. Through a multi-view based workflow proposal, we show the common steps and tools used in imaging genetics analysis, interpolating genotyping, neuroimaging and transcriptomic data. We describe the advantages of existing methods to analyze heterogeneous datasets, using Parkinsons Disease (PD) as a case study. Parkinsons disease is associated with both genetic and neuroimaging factors, however such imaging genetics associations are at an early investigation stage. Therefore it is desirable to have a free and open source workflow that integrates different analysis flows in order to recover potential genetic biomarkers in PD, as in other complex diseases.

bioinformatics↗

Harbor porpoise losing its edges: genetic time series suggests a rapid population decline in Iberian waters over the last 30 years

Impact of climate changes on species is expected to be especially visible at the extremities of the species distribution, where they meet sub-optimal conditions. In Mauritania and Iberia, two genetically isolated populations of harbor porpoises form a distinct ecotype and are presumably locally adapted to the upwelling waters. By analyzing the evolution of mitochondrial genetic variation in the Iberian population between two temporal cohorts (1990-2002 vs. 2012-2015), we report a dramatic decrease in genetic diversity. Phylogenetic analyses including neighboring populations identified two porpoises in southern Iberia carrying a divergent haplotype close to the Mauritanian population, yet forming a distinctive lineage. This suggests that Iberian porpoises may not be as isolated as previously thought with immigration from Mauritania or an unknown population in between, but none from the northern ecotype. The rapid decline in the Iberian mitochondrial diversity may be driven by either genetic drift, or by a dramatic decline in census population size possibly resulting from environmental stochasticity, prey depletion, or acute fishery bycatches. These results illustrate the value of genetics time series to inform demographic trends and emphasize the urgent need for conservation measures to ensure the viability of this small harbor porpoise population in Iberia.

evolutionary biology↗

A gene-based capture assay for surveying patterns of genetic diversity and insecticide resistance in a worldwide group of invasive mosquitoes

Understanding patterns of diversification, genetic exchange, and pesticide resistance in insect species of human health concern is necessary for effective population reduction and management. With the broad availability of next-generation sequencing technologies, one of the best approaches for surveying such patterns involves the simultaneous genotyping of many samples for large numbers of genetic markers from across the known genome. To this end, the targeting of gene sequences of known function or inheritance can be a cost-effective strategy. One insect group of substantial health concern are the mosquito taxa that make up the Culex pipiens complex. Members of this complex transmit damaging arboviruses and filariae worms to humans, as well as other pathogens that are detrimental to endangered vertebrate species such as bird malaria. Here we describe our development of a targeted gene-based assay for surveying genetic diversity and population structure in this mosquito complex. To test the utility of this assay, we examined taxonomic divergence among samples from several members of the complex, as well as distinct populations of the relatively under-studied Culex quinquefasciatus, an urban pantropical species. We also examined the presence of known insecticide-resistance conferring alleles. Broadly, our developed gene-based assay proved effective for examining patterns of taxonomic and geographic clustering within the species complex, as well as for surveying genetic variants that have been associated with insecticide resistance. This assay will be useful for future studies that aim to understand the genetic mechanisms underlying the evolution of ubiquitous and increasingly damaging disease vectors.

genomics↗