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Träfflista för sökning "WFRF:(Jakobsson Mattias) ;pers:(Blum Michael G. B.)"

Sökning: WFRF:(Jakobsson Mattias) > Blum Michael G. B.

  • Resultat 1-9 av 9
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1.
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2.
  • Blum, Michael G. B., et al. (författare)
  • Deep Divergences of Human Gene Trees and Models of Human Origins
  • 2011
  • Ingår i: Molecular biology and evolution. - : Oxford University Press (OUP). - 0737-4038 .- 1537-1719. ; 28:2, s. 889-898
  • Tidskriftsartikel (refereegranskat)abstract
    • Two competing hypotheses are at the forefront of the debate on modern human origins. In the first scenario, known as the recent Out-of-Africa hypothesis, modern humans arose in Africa about 100,000-200,000 years ago and spread throughout the world by replacing the local archaic human populations. By contrast, the second hypothesis posits substantial gene flow between archaic and emerging modern humans. In the last two decades, the young time estimates-between 100,000 and 200,000 years-of the most recent common ancestors for the mitochondrion and the Y chromosome provided evidence in favor of a recent African origin of modern humans. However, the presence of very old lineages for autosonnal and X-linked genes has often been claimed to be incompatible with a simple, single origin of modern humans. Through the analysis of a public DNA sequence database, we find, similar to previous estimates, that the common ancestors of autosomal and X-linked genes are indeed very old, living, on average, respectively, 1,500,000 and 1,000,000 years ago. However, contrary to previous conclusions, we find that these deep gene genealogies are consistent with the Out-of-Africa scenario provided that the ancestral effective population size was approximately 14,000 individuals. We show that an ancient bottleneck in the Middle Pleistocene, possibly arising from an ancestral structured population, can reconcile the contradictory findings from the mitochondrion on the one hand, with the autosomes and the X chromosome on the other hand.
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3.
  • Duforet-Frebourg, Nicolas, et al. (författare)
  • HaploPOP : a software that improves population assignment by combining markers into haplotypes
  • 2015
  • Ingår i: BMC Bioinformatics. - : Springer Science and Business Media LLC. - 1471-2105. ; 16
  • Tidskriftsartikel (refereegranskat)abstract
    • Background: In ecology and forensics, some population assignment techniques use molecular markers to assign individuals to known groups. However, assigning individuals to known populations can be difficult if the level of genetic differentiation among populations is small. Most assignment studies handle independent markers, often by pruning markers in Linkage Disequilibrium (LD), ignoring the information contained in the correlation among markers due to LD. Results: To improve the accuracy of population assignment, we present an algorithm, implemented in the HaploPOP software, that combines markers into haplotypes, without requiring independence. The algorithm is based on the Gain of Informativeness for Assignment that provides a measure to decide if a pair of markers should be combined into haplotypes, or not, in order to improve assignment. Because complete exploration of all possible solutions for constructing haplotypes is computationally prohibitive, our approach uses a greedy algorithm based on windows of fixed sizes. We evaluate the performance of HaploPOP to assign individuals to populations using a split-validation approach. We investigate both simulated SNPs data and dense genotype data from individuals from Spain and Portugal. Conclusions: Our results show that constructing haplotypes with HaploPOP can substantially reduce assignment error. The HaploPOP software is freely available as a command-line software at www.ieg.uu.se/Jakobsson/software/HaploPOP/.
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4.
  • Francois, Olivier, et al. (författare)
  • Demographic history of European populations of Arabidopsis thaliana
  • 2008
  • Ingår i: PLoS Genetics. - : Public Library of Science (PLoS). - 1553-7390 .- 1553-7404. ; 4:5, s. e1000075-
  • Tidskriftsartikel (refereegranskat)abstract
    • The model plant species Arabidopsis thaliana is successful at colonizing land that has recently undergone human-mediated disturbance. To investigate the prehistoric spread of A. thaliana, we applied approximate Bayesian computation and explicit spatial modeling to 76 European accessions sequenced at 876 nuclear loci. We find evidence that a major migration wave occurred from east to west, affecting most of the sampled individuals. The longitudinal gradient appears to result from the plant having spread in Europe from the east ~10,000 years ago, with a rate of westward spread of ~0.9 km/year. This wave-of-advance model is consistent with a natural colonization from an eastern glacial refugium that overwhelmed ancient western lineages. However, the speed and time frame of the model also suggest that the migration of A. thaliana into Europe may have accompanied the spread of agriculture during the Neolithic transition.
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5.
  • Jay, Flora, et al. (författare)
  • Anisotropic Isolation by Distance : The Main Orientations of Human Genetic Differentiation
  • 2013
  • Ingår i: Molecular biology and evolution. - : Oxford University Press (OUP). - 0737-4038 .- 1537-1719. ; 30:3, s. 513-525
  • Tidskriftsartikel (refereegranskat)abstract
    • Genetic differentiation among human populations is greatly influenced by geography due to the accumulation of local allele frequency differences. However, little is known about the possibly different increment of genetic differentiation along the different geographical axes (north-south, east-west, etc.). Here, we provide new methods to examine the asymmetrical patterns of genetic differentiation. We analyzed genome-wide polymorphism data from populations in Africa (n = 29), Asia (n = 26), America (n = 9), and Europe (n = 38), and we found that the major orientations of genetic differentiation are north-south in Europe and Africa, and east-west in Asia, but no preferential orientation was found in the Americas. Additionally, we showed that the localization of the individual geographic origins based on single nucleotide polymorphism data was not equally precise along all orientations. Confirming our findings, we obtained that, in each continent, the orientation along which the precision is maximal corresponds to the orientation of maximum differentiation. Our results have implications for interpreting human genetic variation in terms of isolation by distance and spatial range expansion processes. In Europe, for instance, the precise northnorthwest-southsoutheast axis of main European differentiation cannot be explained by a simple Neolithic demic diffusion model without admixture with the local populations because in that case the orientation of greatest differentiation should be perpendicular to the direction of expansion. In addition to humans, anisotropic analyses can guide the description of genetic differentiation for other organisms and provide information on expansions of invasive species or the processes of plant dispersal.
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6.
  • Schlebusch, Carina M., et al. (författare)
  • Genomic Variation in Seven Khoe-San Groups Reveals Adaptation and Complex African History
  • 2012
  • Ingår i: Science. - : American Association for the Advancement of Science (AAAS). - 0036-8075 .- 1095-9203. ; 338:6105, s. 374-379
  • Tidskriftsartikel (refereegranskat)abstract
    • The history of click-speaking Khoe-San, and African populations in general, remains poorly understood. We genotyped ∼2.3 million SNPs in 220 southern Africans and found that the Khoe-San diverged from other populations ≥100,000 years ago, but structure within the Khoe-San dated back to about 35,000 years ago. Genetic variation in various sub-Saharan populations did not localize the origin of modern humans to a single geographic region within Africa; instead, it indicated a history of admixture and stratification. We found evidence of adaptation targeting muscle function and immune response, potential adaptive introgression of UV-light protection, and selection predating modern human diversification involving skeletal and neurological development. These new findings illustrate the importance of African genomic diversity in understanding human evolutionary history.
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7.
  • Sjödin, Per, et al. (författare)
  • Resequencing Data Provide No Evidence for a Human Bottleneck in Africa during the Penultimate Glacial Period
  • 2012
  • Ingår i: Molecular biology and evolution. - : Oxford University Press (OUP). - 0737-4038 .- 1537-1719. ; 29:7, s. 1851-1860
  • Tidskriftsartikel (refereegranskat)abstract
    • Based on the accumulation of genetic, climatic, and fossil evidence, a central theory in paleoanthropology stipulates that a demographic bottleneck coincided with the origin of our species Homo Sapiens. This theory proposes that anatomically modern humans-which were only present in Africa at the time-experienced a drastic bottleneck during the penultimate glacial age (130-190 kya) when a cold and dry climate prevailed. Two scenarios have been proposed to describe the bottleneck, which involve either a fragmentation of the range occupied by humans or the survival of one small group of humans. Here, we analyze DNA sequence data from 61 nuclear loci sequenced in three African populations using Approximate Bayesian Computation and numerical simulations. In contrast to the bottleneck theory, we show that a simple model without any bottleneck during the penultimate ice age has the greatest statistical support compared with bottleneck models. Although the proposed bottleneck is ancient, occurring at least 130 kya, we can discard the possibility that it did not leave detectable footprints in the DNA sequence data except if the bottleneck involves a less than a 3-fold reduction in population size. Finally, we confirm that a simple model without a bottleneck is able to reproduce the main features of the observed patterns of genetic variation. We conclude that models of Pleistocene refugium for modern human origins now require substantial revision.
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8.
  • Sjöstrand, Agnès E. (författare)
  • Origins and Adaptation in Humans : A Case Study of Taste and Lifestyle
  • 2015
  • Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • In this thesis, I use population genetics and statistical approaches to investigate early human demography, infer local adaptation in diverse sets of populations, and study the genetic basis for taste perception.In the first paper, I examine the genomic evidence for a severe bottleneck, which has been suggested based on paleontological and climate studies to coincide with the emergence of anatomically modern humans. Using a Bayesian approach, I evaluate the genetic evidence of a bottleneck between 190,000 and 130,000 years ago and find that the data is in favor of a model without bottleneck at this time point.I further develop a method to detect local adaptation based on frequencies of private haplotypes. I first show, using simulated data, that this method can detect local adaption. Applied to large-scale human genotype data, this method detects known signals of positive selection in human data such as the positive selection around the lactase gene in Europeans and East Africans. Also, this method permits to improve knowledge on potential adaptation events in humans as it finds several regions potentially selected that were not previously described. I further investigate patterns of adaptation in whole genome data based on a diverse set of African populations. The results from the regions potentially selected show that diet and pathogens are the common driving forces of adaptation in all studied populations.There is evidence that taste perception have evolved in concert with diet, environment, and the organismal needs in humans. For this reason, I study taste perception in populations differing on lifestyle (hunter-gatherers, farmers and nomad herders). I present taste perception phenotypes for all tastes (sweet, bitter, sour, salty and umami) and relate them to high density genotype data. I show that taste and taste-involved genes have evolved with lifestyle. By performing an association study, I also show that variation in taste perception involves more genes than only the taste receptors genes.In this thesis, by analyzing human genetic data with a population genetics approaches, I covered several topics of human ancient demography and adaptation and show the utility of using large-scale genetic data to better understand human history.
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9.
  • Sjöstrand, Agnès E., et al. (författare)
  • Taste perception and lifestyle : insights from phenotype and genome data among Africans and Asians
  • 2021
  • Ingår i: European Journal of Human Genetics. - : Springer Nature. - 1018-4813 .- 1476-5438. ; 29, s. 325-337
  • Tidskriftsartikel (refereegranskat)abstract
    • Taste is essential for the interaction of animals with their food and has co-evolved with diet. Humans have peopled a large range of environments and present a wide range of diets, but little is known about the diversity and evolution of human taste perception. We measured taste recognition thresholds across populations differing in lifestyles (hunter gatherers and farmers from Central Africa, nomad herders, and farmers from Central Asia). We also generated genome-wide genotype data and performed association studies and selection scans in order to link the phenotypic variation in taste sensitivity with genetic variation. We found that hunter gatherers have lower overall sensitivity as well as lower sensitivity to quinine and fructose than their farming neighbors. In parallel, there is strong population divergence in genes associated with tongue morphogenesis and genes involved in the transduction pathway of taste signals in the African populations. We find signals of recent selection in bitter taste-receptor genes for all four populations. Enrichment analysis on association scans for the various tastes confirmed already documented associations and revealed novel GO terms that are good candidates for being involved in taste perception. Our framework permitted us to gain insight into the genetic basis of taste sensitivity variation across populations and lifestyles.
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