RESUMEN
Gibbons are small arboreal apes that display an accelerated rate of evolutionary chromosomal rearrangement and occupy a key node in the primate phylogeny between Old World monkeys and great apes. Here we present the assembly and analysis of a northern white-cheeked gibbon (Nomascus leucogenys) genome. We describe the propensity for a gibbon-specific retrotransposon (LAVA) to insert into chromosome segregation genes and alter transcription by providing a premature termination site, suggesting a possible molecular mechanism for the genome plasticity of the gibbon lineage. We further show that the gibbon genera (Nomascus, Hylobates, Hoolock and Symphalangus) experienced a near-instantaneous radiation â¼5 million years ago, coincident with major geographical changes in southeast Asia that caused cycles of habitat compression and expansion. Finally, we identify signatures of positive selection in genes important for forelimb development (TBX5) and connective tissues (COL1A1) that may have been involved in the adaptation of gibbons to their arboreal habitat.
Asunto(s)
Genoma/genética , Hylobates/clasificación , Hylobates/genética , Cariotipo , Filogenia , Animales , Evolución Molecular , Hominidae/clasificación , Hominidae/genética , Humanos , Datos de Secuencia Molecular , Retroelementos/genética , Selección Genética , Terminación de la Transcripción GenéticaRESUMEN
Cichlid fishes are famous for large, diverse and replicated adaptive radiations in the Great Lakes of East Africa. To understand the molecular mechanisms underlying cichlid phenotypic diversity, we sequenced the genomes and transcriptomes of five lineages of African cichlids: the Nile tilapia (Oreochromis niloticus), an ancestral lineage with low diversity; and four members of the East African lineage: Neolamprologus brichardi/pulcher (older radiation, Lake Tanganyika), Metriaclima zebra (recent radiation, Lake Malawi), Pundamilia nyererei (very recent radiation, Lake Victoria), and Astatotilapia burtoni (riverine species around Lake Tanganyika). We found an excess of gene duplications in the East African lineage compared to tilapia and other teleosts, an abundance of non-coding element divergence, accelerated coding sequence evolution, expression divergence associated with transposable element insertions, and regulation by novel microRNAs. In addition, we analysed sequence data from sixty individuals representing six closely related species from Lake Victoria, and show genome-wide diversifying selection on coding and regulatory variants, some of which were recruited from ancient polymorphisms. We conclude that a number of molecular mechanisms shaped East African cichlid genomes, and that amassing of standing variation during periods of relaxed purifying selection may have been important in facilitating subsequent evolutionary diversification.
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Cíclidos/clasificación , Cíclidos/genética , Evolución Molecular , Especiación Genética , Genoma/genética , África Oriental , Animales , Elementos Transponibles de ADN/genética , Duplicación de Gen/genética , Regulación de la Expresión Génica/genética , Genómica , Lagos , MicroARNs/genética , Filogenia , Polimorfismo Genético/genéticaRESUMEN
The discovery of a living coelacanth specimen in 1938 was remarkable, as this lineage of lobe-finned fish was thought to have become extinct 70 million years ago. The modern coelacanth looks remarkably similar to many of its ancient relatives, and its evolutionary proximity to our own fish ancestors provides a glimpse of the fish that first walked on land. Here we report the genome sequence of the African coelacanth, Latimeria chalumnae. Through a phylogenomic analysis, we conclude that the lungfish, and not the coelacanth, is the closest living relative of tetrapods. Coelacanth protein-coding genes are significantly more slowly evolving than those of tetrapods, unlike other genomic features. Analyses of changes in genes and regulatory elements during the vertebrate adaptation to land highlight genes involved in immunity, nitrogen excretion and the development of fins, tail, ear, eye, brain and olfaction. Functional assays of enhancers involved in the fin-to-limb transition and in the emergence of extra-embryonic tissues show the importance of the coelacanth genome as a blueprint for understanding tetrapod evolution.
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Evolución Biológica , Peces/clasificación , Peces/genética , Genoma/genética , Animales , Animales Modificados Genéticamente , Embrión de Pollo , Secuencia Conservada/genética , Elementos de Facilitación Genéticos/genética , Evolución Molecular , Extremidades/anatomía & histología , Extremidades/crecimiento & desarrollo , Peces/anatomía & histología , Peces/fisiología , Genes Homeobox/genética , Genómica , Inmunoglobulina M/genética , Ratones , Anotación de Secuencia Molecular , Datos de Secuencia Molecular , Filogenia , Alineación de Secuencia , Análisis de Secuencia de ADN , Vertebrados/anatomía & histología , Vertebrados/genética , Vertebrados/fisiologíaRESUMEN
The comparison of related genomes has emerged as a powerful lens for genome interpretation. Here we report the sequencing and comparative analysis of 29 eutherian genomes. We confirm that at least 5.5% of the human genome has undergone purifying selection, and locate constrained elements covering â¼4.2% of the genome. We use evolutionary signatures and comparisons with experimental data sets to suggest candidate functions for â¼60% of constrained bases. These elements reveal a small number of new coding exons, candidate stop codon readthrough events and over 10,000 regions of overlapping synonymous constraint within protein-coding exons. We find 220 candidate RNA structural families, and nearly a million elements overlapping potential promoter, enhancer and insulator regions. We report specific amino acid residues that have undergone positive selection, 280,000 non-coding elements exapted from mobile elements and more than 1,000 primate- and human-accelerated elements. Overlap with disease-associated variants indicates that our findings will be relevant for studies of human biology, health and disease.
Asunto(s)
Evolución Molecular , Genoma Humano/genética , Genoma/genética , Mamíferos/genética , Animales , Enfermedad , Exones/genética , Genómica , Salud , Humanos , Anotación de Secuencia Molecular , Filogenia , ARN/clasificación , ARN/genética , Selección Genética/genética , Alineación de Secuencia , Análisis de Secuencia de ADNRESUMEN
Genetic variation allows the malaria parasite Plasmodium falciparum to overcome chemotherapeutic agents, vaccines and vector control strategies and remain a leading cause of global morbidity and mortality. Here we describe an initial survey of genetic variation across the P. falciparum genome. We performed extensive sequencing of 16 geographically diverse parasites and identified 46,937 SNPs, demonstrating rich diversity among P. falciparum parasites (pi = 1.16 x 10(-3)) and strong correlation with gene function. We identified multiple regions with signatures of selective sweeps in drug-resistant parasites, including a previously unidentified 160-kb region with extremely low polymorphism in pyrimethamine-resistant parasites. We further characterized 54 worldwide isolates by genotyping SNPs across 20 genomic regions. These data begin to define population structure among African, Asian and American groups and illustrate the degree of linkage disequilibrium, which extends over relatively short distances in African parasites but over longer distances in Asian parasites. We provide an initial map of genetic diversity in P. falciparum and demonstrate its potential utility in identifying genes subject to recent natural selection and in understanding the population genetics of this parasite.
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Mapeo Cromosómico/métodos , Variación Genética , Genoma de Protozoos , Plasmodium falciparum/genética , África , Animales , Asia , América Central , Genotipo , Humanos , Filogenia , Polimorfismo de Nucleótido Simple , América del SurRESUMEN
Exceptionally accurate genome reference sequences have proven to be of great value to microbial researchers. Thus, to date, about 1800 bacterial genome assemblies have been "finished" at great expense with the aid of manual laboratory and computational processes that typically iterate over a period of months or even years. By applying a new laboratory design and new assembly algorithm to 16 samples, we demonstrate that assemblies exceeding finished quality can be obtained from whole-genome shotgun data and automated computation. Cost and time requirements are thus dramatically reduced.
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Bacterias/genética , Genoma Bacteriano , Biblioteca Genómica , Análisis de Secuencia de ADN/métodos , AlgoritmosRESUMEN
Phytophthora infestans is the most destructive pathogen of potato and a model organism for the oomycetes, a distinct lineage of fungus-like eukaryotes that are related to organisms such as brown algae and diatoms. As the agent of the Irish potato famine in the mid-nineteenth century, P. infestans has had a tremendous effect on human history, resulting in famine and population displacement. To this day, it affects world agriculture by causing the most destructive disease of potato, the fourth largest food crop and a critical alternative to the major cereal crops for feeding the world's population. Current annual worldwide potato crop losses due to late blight are conservatively estimated at $6.7 billion. Management of this devastating pathogen is challenged by its remarkable speed of adaptation to control strategies such as genetically resistant cultivars. Here we report the sequence of the P. infestans genome, which at approximately 240 megabases (Mb) is by far the largest and most complex genome sequenced so far in the chromalveolates. Its expansion results from a proliferation of repetitive DNA accounting for approximately 74% of the genome. Comparison with two other Phytophthora genomes showed rapid turnover and extensive expansion of specific families of secreted disease effector proteins, including many genes that are induced during infection or are predicted to have activities that alter host physiology. These fast-evolving effector genes are localized to highly dynamic and expanded regions of the P. infestans genome. This probably plays a crucial part in the rapid adaptability of the pathogen to host plants and underpins its evolutionary potential.
Asunto(s)
Genoma/genética , Phytophthora infestans/genética , Enfermedades de las Plantas/microbiología , Solanum tuberosum/microbiología , Proteínas Algáceas/genética , Elementos Transponibles de ADN/genética , ADN Intergénico/genética , Evolución Molecular , Interacciones Huésped-Patógeno/genética , Humanos , Irlanda , Datos de Secuencia Molecular , Necrosis , Fenotipo , Phytophthora infestans/patogenicidad , Enfermedades de las Plantas/inmunología , Solanum tuberosum/inmunología , InaniciónRESUMEN
Deep sequencing technologies have the potential to transform the study of highly variable viral pathogens by providing a rapid and cost-effective approach to sensitively characterize rapidly evolving viral quasispecies. Here, we report on a high-throughput whole HIV-1 genome deep sequencing platform that combines 454 pyrosequencing with novel assembly and variant detection algorithms. In one subject we combined these genetic data with detailed immunological analyses to comprehensively evaluate viral evolution and immune escape during the acute phase of HIV-1 infection. The majority of early, low frequency mutations represented viral adaptation to host CD8+ T cell responses, evidence of strong immune selection pressure occurring during the early decline from peak viremia. CD8+ T cell responses capable of recognizing these low frequency escape variants coincided with the selection and evolution of more effective secondary HLA-anchor escape mutations. Frequent, and in some cases rapid, reversion of transmitted mutations was also observed across the viral genome. When located within restricted CD8 epitopes these low frequency reverting mutations were sufficient to prime de novo responses to these epitopes, again illustrating the capacity of the immune response to recognize and respond to low frequency variants. More importantly, rapid viral escape from the most immunodominant CD8+ T cell responses coincided with plateauing of the initial viral load decline in this subject, suggestive of a potential link between maintenance of effective, dominant CD8 responses and the degree of early viremia reduction. We conclude that the early control of HIV-1 replication by immunodominant CD8+ T cell responses may be substantially influenced by rapid, low frequency viral adaptations not detected by conventional sequencing approaches, which warrants further investigation. These data support the critical need for vaccine-induced CD8+ T cell responses to target more highly constrained regions of the virus in order to ensure the maintenance of immunodominant CD8 responses and the sustained decline of early viremia.
Asunto(s)
Genoma Viral/genética , Estudio de Asociación del Genoma Completo , Infecciones por VIH/virología , VIH-1/genética , Evasión Inmune/inmunología , Linfocitos T CD8-positivos/inmunología , Variación Genética , Variación Estructural del Genoma , Infecciones por VIH/inmunología , Infecciones por VIH/prevención & control , VIH-1/inmunología , VIH-1/patogenicidad , Humanos , Evasión Inmune/genética , Análisis de Secuencia por Matrices de Oligonucleótidos , ARN Viral/análisis , Análisis de Secuencia de ARN , Vacunas Virales/inmunologíaRESUMEN
Massively parallel DNA sequencing technologies are revolutionizing genomics by making it possible to generate billions of relatively short (~100-base) sequence reads at very low cost. Whereas such data can be readily used for a wide range of biomedical applications, it has proven difficult to use them to generate high-quality de novo genome assemblies of large, repeat-rich vertebrate genomes. To date, the genome assemblies generated from such data have fallen far short of those obtained with the older (but much more expensive) capillary-based sequencing approach. Here, we report the development of an algorithm for genome assembly, ALLPATHS-LG, and its application to massively parallel DNA sequence data from the human and mouse genomes, generated on the Illumina platform. The resulting draft genome assemblies have good accuracy, short-range contiguity, long-range connectivity, and coverage of the genome. In particular, the base accuracy is high (≥99.95%) and the scaffold sizes (N50 size = 11.5 Mb for human and 7.2 Mb for mouse) approach those obtained with capillary-based sequencing. The combination of improved sequencing technology and improved computational methods should now make it possible to increase dramatically the de novo sequencing of large genomes. The ALLPATHS-LG program is available at http://www.broadinstitute.org/science/programs/genome-biology/crd.
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Algoritmos , Genómica/métodos , Análisis de Secuencia de ADN/métodos , Programas Informáticos , Animales , Genoma/genética , Humanos , Internet , Ratones , Reproducibilidad de los ResultadosRESUMEN
BACKGROUND: Extensive genetic diversity in viral populations within infected hosts and the divergence of variants from existing reference genomes impede the analysis of deep viral sequencing data. A de novo population consensus assembly is valuable both as a single linear representation of the population and as a backbone on which intra-host variants can be accurately mapped. The availability of consensus assemblies and robustly mapped variants are crucial to the genetic study of viral disease progression, transmission dynamics, and viral evolution. Existing de novo assembly techniques fail to robustly assemble ultra-deep sequence data from genetically heterogeneous populations such as viruses into full-length genomes due to the presence of extensive genetic variability, contaminants, and variable sequence coverage. RESULTS: We present VICUNA, a de novo assembly algorithm suitable for generating consensus assemblies from genetically heterogeneous populations. We demonstrate its effectiveness on Dengue, Human Immunodeficiency and West Nile viral populations, representing a range of intra-host diversity. Compared to state-of-the-art assemblers designed for haploid or diploid systems, VICUNA recovers full-length consensus and captures insertion/deletion polymorphisms in diverse samples. Final assemblies maintain a high base calling accuracy. VICUNA program is publicly available at: http://www.broadinstitute.org/scientific-community/science/projects/viral-genomics/ viral-genomics-analysis-software. CONCLUSIONS: We developed VICUNA, a publicly available software tool, that enables consensus assembly of ultra-deep sequence derived from diverse viral populations. While VICUNA was developed for the analysis of viral populations, its application to other heterogeneous sequence data sets such as metagenomic or tumor cell population samples may prove beneficial in these fields of research.
Asunto(s)
Genoma Viral/genética , Programas Informáticos , Algoritmos , Biología ComputacionalRESUMEN
The genetic divergence time between two species varies substantially across the genome, conveying important information about the timing and process of speciation. Here we develop a framework for studying this variation and apply it to about 20 million base pairs of aligned sequence from humans, chimpanzees, gorillas and more distantly related primates. Human-chimpanzee genetic divergence varies from less than 84% to more than 147% of the average, a range of more than 4 million years. Our analysis also shows that human-chimpanzee speciation occurred less than 6.3 million years ago and probably more recently, conflicting with some interpretations of ancient fossils. Most strikingly, chromosome X shows an extremely young genetic divergence time, close to the genome minimum along nearly its entire length. These unexpected features would be explained if the human and chimpanzee lineages initially diverged, then later exchanged genes before separating permanently.
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Especiación Genética , Pan troglodytes/genética , Animales , Evolución Molecular , Genoma , Genómica , Humanos , Hibridación Genética , Modelos Genéticos , Primates/genética , Factores de Tiempo , Cromosoma X/genéticaRESUMEN
Chromosome 17 is unusual among the human chromosomes in many respects. It is the largest human autosome with orthology to only a single mouse chromosome, mapping entirely to the distal half of mouse chromosome 11. Chromosome 17 is rich in protein-coding genes, having the second highest gene density in the genome. It is also enriched in segmental duplications, ranking third in density among the autosomes. Here we report a finished sequence for human chromosome 17, as well as a structural comparison with the finished sequence for mouse chromosome 11, the first finished mouse chromosome. Comparison of the orthologous regions reveals striking differences. In contrast to the typical pattern seen in mammalian evolution, the human sequence has undergone extensive intrachromosomal rearrangement, whereas the mouse sequence has been remarkably stable. Moreover, although the human sequence has a high density of segmental duplication, the mouse sequence has a very low density. Notably, these segmental duplications correspond closely to the sites of structural rearrangement, demonstrating a link between duplication and rearrangement. Examination of the main classes of duplicated segments provides insight into the dynamics underlying expansion of chromosome-specific, low-copy repeats in the human genome.
Asunto(s)
Cromosomas Humanos Par 17/genética , Evolución Molecular , Animales , Composición de Base , Duplicación de Gen , Humanos , Elementos de Nucleótido Esparcido Largo/genética , Ratones , Análisis de Secuencia de ADN , Elementos de Nucleótido Esparcido Corto/genética , Sintenía/genéticaRESUMEN
Here we report a high-quality draft genome sequence of the domestic dog (Canis familiaris), together with a dense map of single nucleotide polymorphisms (SNPs) across breeds. The dog is of particular interest because it provides important evolutionary information and because existing breeds show great phenotypic diversity for morphological, physiological and behavioural traits. We use sequence comparison with the primate and rodent lineages to shed light on the structure and evolution of genomes and genes. Notably, the majority of the most highly conserved non-coding sequences in mammalian genomes are clustered near a small subset of genes with important roles in development. Analysis of SNPs reveals long-range haplotypes across the entire dog genome, and defines the nature of genetic diversity within and across breeds. The current SNP map now makes it possible for genome-wide association studies to identify genes responsible for diseases and traits, with important consequences for human and companion animal health.
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Perros/genética , Evolución Molecular , Genoma/genética , Genómica , Haplotipos/genética , Animales , Secuencia Conservada/genética , Enfermedades de los Perros/genética , Perros/clasificación , Femenino , Humanos , Hibridación Genética , Masculino , Ratones , Mutagénesis/genética , Polimorfismo de Nucleótido Simple/genética , Ratas , Elementos de Nucleótido Esparcido Corto/genética , Sintenía/genéticaRESUMEN
Population geneticists often study small numbers of carefully chosen loci, but it has become possible to obtain orders of magnitude for more data from overlaps of genome sequences. Here, we generate tens of millions of base pairs of multiple sequence alignments from combinations of three western chimpanzees, three central chimpanzees, an eastern chimpanzee, a bonobo, a human, an orangutan, and a macaque. Analysis provides a more precise understanding of demographic history than was previously available. We show that bonobos and common chimpanzees were separated approximately 1,290,000 years ago, western and other common chimpanzees approximately 510,000 years ago, and eastern and central chimpanzees at least 50,000 years ago. We infer that the central chimpanzee population size increased by at least a factor of 4 since its separation from western chimpanzees, while the western chimpanzee effective population size decreased. Surprisingly, in about one percent of the genome, the genetic relationships between humans, chimpanzees, and bonobos appear to be different from the species relationships. We used PCR-based resequencing to confirm 11 regions where chimpanzees and bonobos are not most closely related. Study of such loci should provide information about the period of time 5-7 million years ago when the ancestors of humans separated from those of the chimpanzees.
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Evolución Molecular , Genética de Población , Genoma , Pan troglodytes/genética , Animales , Variación Genética , Genoma Humano , Genómica , Humanos , Pan paniscus/genética , Alineación de SecuenciaRESUMEN
Accurate identification of tumor-derived somatic variants in plasma circulating cell-free DNA (cfDNA) requires understanding of the various biological compartments contributing to the cfDNA pool. We sought to define the technical feasibility of a high-intensity sequencing assay of cfDNA and matched white blood cell DNA covering a large genomic region (508 genes; 2 megabases; >60,000× raw depth) in a prospective study of 124 patients with metastatic cancer, with contemporaneous matched tumor tissue biopsies, and 47 controls without cancer. The assay displayed high sensitivity and specificity, allowing for de novo detection of tumor-derived mutations and inference of tumor mutational burden, microsatellite instability, mutational signatures and sources of somatic mutations identified in cfDNA. The vast majority of cfDNA mutations (81.6% in controls and 53.2% in patients with cancer) had features consistent with clonal hematopoiesis. This cfDNA sequencing approach revealed that clonal hematopoiesis constitutes a pervasive biological phenomenon, emphasizing the importance of matched cfDNA-white blood cell sequencing for accurate variant interpretation.
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Ácidos Nucleicos Libres de Células/sangre , ADN Tumoral Circulante/sangre , Genómica , Neoplasias/sangre , Adulto , Biomarcadores de Tumor/sangre , ADN Tumoral Circulante/genética , Análisis Mutacional de ADN , ADN de Neoplasias/sangre , Femenino , Regulación Neoplásica de la Expresión Génica , Secuenciación de Nucleótidos de Alto Rendimiento , Humanos , Masculino , Inestabilidad de Microsatélites , Persona de Mediana Edad , Mutación , Neoplasias/genética , Neoplasias/patologíaRESUMEN
Purpose: Tumor-derived cell-free DNA (cfDNA) in plasma can be used for molecular testing and provide an attractive alternative to tumor tissue. Commonly used PCR-based technologies can test for limited number of alterations at the time. Therefore, novel ultrasensitive technologies capable of testing for a broad spectrum of molecular alterations are needed to further personalized cancer therapy.Experimental Design: We developed a highly sensitive ultradeep next-generation sequencing (NGS) assay using reagents from TruSeqNano library preparation and NexteraRapid Capture target enrichment kits to generate plasma cfDNA sequencing libraries for mutational analysis in 61 cancer-related genes using common bioinformatics tools. The results were retrospectively compared with molecular testing of archival primary or metastatic tumor tissue obtained at different points of clinical care.Results: In a study of 55 patients with advanced cancer, the ultradeep NGS assay detected 82% (complete detection) to 87% (complete and partial detection) of the aberrations identified in discordantly collected corresponding archival tumor tissue. Patients with a low variant allele frequency (VAF) of mutant cfDNA survived longer than those with a high VAF did (P = 0.018). In patients undergoing systemic therapy, radiological response was positively associated with changes in cfDNA VAF (P = 0.02), and compared with unchanged/increased mutant cfDNA VAF, decreased cfDNA VAF was associated with longer time to treatment failure (TTF; P = 0.03).Conclusions: Ultradeep NGS assay has good sensitivity compared with conventional clinical mutation testing of archival specimens. A high VAF in mutant cfDNA corresponded with shorter survival. Changes in VAF of mutated cfDNA were associated with TTF. Clin Cancer Res; 23(18); 5648-56. ©2017 AACR.
Asunto(s)
Biomarcadores de Tumor , ADN Tumoral Circulante , Secuenciación de Nucleótidos de Alto Rendimiento , Neoplasias/diagnóstico , Neoplasias/genética , Adulto , Anciano , Anciano de 80 o más Años , Femenino , Pruebas Genéticas , Secuenciación de Nucleótidos de Alto Rendimiento/métodos , Secuenciación de Nucleótidos de Alto Rendimiento/normas , Humanos , Masculino , Persona de Mediana Edad , Mutación , Neoplasias/mortalidad , Pronóstico , Reproducibilidad de los Resultados , Sensibilidad y EspecificidadRESUMEN
BACKGROUND: The process of generating raw genome sequence data continues to become cheaper, faster, and more accurate. However, assembly of such data into high-quality, finished genome sequences remains challenging. Many genome assembly tools are available, but they differ greatly in terms of their performance (speed, scalability, hardware requirements, acceptance of newer read technologies) and in their final output (composition of assembled sequence). More importantly, it remains largely unclear how to best assess the quality of assembled genome sequences. The Assemblathon competitions are intended to assess current state-of-the-art methods in genome assembly. RESULTS: In Assemblathon 2, we provided a variety of sequence data to be assembled for three vertebrate species (a bird, a fish, and snake). This resulted in a total of 43 submitted assemblies from 21 participating teams. We evaluated these assemblies using a combination of optical map data, Fosmid sequences, and several statistical methods. From over 100 different metrics, we chose ten key measures by which to assess the overall quality of the assemblies. CONCLUSIONS: Many current genome assemblers produced useful assemblies, containing a significant representation of their genes and overall genome structure. However, the high degree of variability between the entries suggests that there is still much room for improvement in the field of genome assembly and that approaches which work well in assembling the genome of one species may not necessarily work well for another.
RESUMEN
Mutations are the raw material of evolution but have been difficult to study directly. We report the largest study of new mutations to date, comprising 2,058 germline changes discovered by analyzing 85,289 Icelanders at 2,477 microsatellites. The paternal-to-maternal mutation rate ratio is 3.3, and the rate in fathers doubles from age 20 to 58, whereas there is no association with age in mothers. Longer microsatellite alleles are more mutagenic and tend to decrease in length, whereas the opposite is seen for shorter alleles. We use these empirical observations to build a model that we apply to individuals for whom we have both genome sequence and microsatellite data, allowing us to estimate key parameters of evolution without calibration to the fossil record. We infer that the sequence mutation rate is 1.4-2.3×10(-8) mutations per base pair per generation (90% credible interval) and that human-chimpanzee speciation occurred 3.7-6.6 million years ago.
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Genoma Humano , Mutación de Línea Germinal , Repeticiones de Microsatélite , Teorema de Bayes , Evolución Molecular , Femenino , Especiación Genética , Humanos , Masculino , Cadenas de Markov , Modelos Genéticos , Método de Montecarlo , LinajeRESUMEN
Several studies have found evidence for more positive selection on the chimpanzee lineage compared with the human lineage since the two species split. A potential concern, however, is that these findings may simply reflect artifacts of the data: inaccuracies in the underlying chimpanzee genome sequence, which is of lower quality than human. To test this hypothesis, we generated de novo genome assemblies of chimpanzee and macaque and aligned them with human. We also implemented a novel bioinformatic procedure for producing alignments of closely related species that uses synteny information to remove misassembled and misaligned regions, and sequence quality scores to remove nucleotides that are less reliable. We applied this procedure to re-examine 59 genes recently identified as candidates for positive selection in chimpanzees. The great majority of these signals disappear after application of our new bioinformatic procedure. We also carried out laboratory-based resequencing of 10 of the regions in multiple chimpanzees and humans, and found that our alignments were correct wherever there was a conflict with the published results. These findings throw into question previous findings that there has been more positive selection in chimpanzees than in humans since the two species diverged. Our study also highlights the challenges of searching the extreme tails of distributions for signals of natural selection. Inaccuracies in the genome sequence at even a tiny fraction of genes can produce false-positive signals, which make it difficult to identify loci that have genuinely been targets of selection.
Asunto(s)
Genoma , Selección Genética , Análisis de Secuencia de ADN , Animales , Secuencia de Bases , Evolución Molecular , Genómica , Humanos , Datos de Secuencia Molecular , Pan troglodytes/genética , Alineación de Secuencia , SinteníaRESUMEN
We describe a new assembly algorithm, where a genome assembly with low sequence coverage, either throughout the genome or locally, due to cloning bias, is considerably improved through an assisting process via a related genome. We show that the information provided by aligning the whole-genome shotgun reads of the target against a reference genome can be used to substantially improve the quality of the resulting assembly.