Genome Graphs

Mapping Intimacies ◽

10.1101/101378 ◽

2017 ◽

Cited By ~ 34

Author(s):

Adam M. Novak ◽

Glenn Hickey ◽

Erik Garrison ◽

Sean Blum ◽

Abram Connelly ◽

...

Keyword(s):

Reference Genome ◽

Human Genetics ◽

De Novo ◽

Variant Calling ◽

Reference Structure ◽

Read Mapping ◽

Human Reference Genome ◽

A Genome ◽

Universal Reference ◽

Genome Graph

AbstractThere is increasing recognition that a single, monoploid reference genome is a poor universal reference structure for human genetics, because it represents only a tiny fraction of human variation. Adding this missing variation results in a structure that can be described as a mathematical graph: a genome graph. We demonstrate that, in comparison to the existing reference genome (GRCh38), genome graphs can substantially improve the fractions of reads that map uniquely and perfectly. Furthermore, we show that this fundamental simplification of read mapping transforms the variant calling problem from one in which many non-reference variants must be discovered de-novo to one in which the vast majority of variants are simply re-identified within the graph. Using standard benchmarks as well as a novel reference-free evaluation, we show that a simplistic variant calling procedure on a genome graph can already call variants at least as well as, and in many cases better than, a state-of-the-art method on the linear human reference genome. We anticipate that graph-based references will supplant linear references in humans and in other applications where cohorts of sequenced individuals are available.

Genome Graphs and the Evolution of Genome Inference

10.1101/101816 ◽

2017 ◽

Cited By ~ 2

Author(s):

Benedict Paten ◽

Adam M. Novak ◽

Jordan M. Eizenga ◽

Garrison Erik

Keyword(s):

Reference Genome ◽

Variant Calling ◽

Modern Human ◽

Human Biology ◽

Scientific Achievement ◽

Read Mapping ◽

Human Genomics ◽

Human Reference Genome ◽

Human Genomes ◽

Reference Bias

AbstractThe human reference genome is part of the foundation of modern human biology, and a monumental scientific achievement. However, because it excludes a great deal of common human variation, it introduces a pervasive reference bias into the field of human genomics. To reduce this bias, it makes sense to draw on representative collections of human genomes, brought together into reference cohorts. There are a number of techniques to represent and organize data gleaned from these cohorts, many using ideas implicitly or explicitly borrowed from graph based models. Here, we survey various projects underway to build and apply these graph based structures—which we collectively refer to as genome graphs—and discuss the improvements in read mapping, variant calling, and haplotype determination that genome graphs are expected to produce.

Enabling multiscale variation analysis with genome graphs

10.1101/2021.02.03.429603 ◽

2021 ◽

Author(s):

Brice Letcher ◽

Martin Hunt ◽

Zamin Iqbal

Keyword(s):

Genetic Variation ◽

Directed Acyclic Graph ◽

Structural Variation ◽

Reference Genome ◽

Multiple Scales ◽

State Of The Art ◽

Variant Calling ◽

Variation Analysis ◽

New Algorithms ◽

Genome Graph

AbstractBackgroundStandard approaches to characterising genetic variation revolve around mapping reads to a reference genome and describing variants in terms of differences from the reference; this is based on the assumption that these differences will be small and provides a simple coordinate system. However this fails, and the coordinates break down, when there are diverged haplotypes at a locus (e.g. one haplotype contains a multi-kilobase deletion, a second contains a few SNPs, and a third is highly diverged with hundreds of SNPs). To handle these, we need to model genetic variation that occurs at different length-scales (SNPs to large structural variants) and that occurs on alternate backgrounds. We refer to these together as multiscale variation.ResultsWe model the genome as a directed acyclic graph consisting of successive hierarchical subgraphs (“sites”) that naturally incorporate multiscale variation, and introduce an algorithm for genotyping, implemented in the software gramtools. This enables variant calling on different sequence backgrounds. In addition to producing regular VCF files, we introduce a JSON file format based on VCF, which records variant site relationships and alternate sequence backgrounds.We show two applications. First, we benchmark gramtools against existing state-of-the-art methods in joint-genotyping 17 M. tuberculosis samples at long deletions and the overlapping small variants that segregate in a cohort of 1,017 genomes. Second, in 706 African and SE Asian P. falciparum genomes, we analyse a dimorphic surface antigen gene which possesses variation on two diverged backgrounds which appeared to not recombine. This generates the first map of variation on both backgrounds, revealing patterns of recombination that were previously unknown.ConclusionsWe need new approaches to be able to jointly analyse SNP and structural variation in cohorts, and even more to handle variants on different genetic backgrounds. We have demonstrated that by modelling with a directed, acyclic and locally hierarchical genome graph, we can apply new algorithms to accurately genotype dense variation at multiple scales. We also propose a generalisation of VCF for accessing multiscale variation in genome graphs, which we hope will be of wide utility.

Genome assembly of the JD17 soybean provides a new reference genome for Comparative genomics

10.1101/2021.11.23.469778 ◽

2021 ◽

Author(s):

Xinxin Yi ◽

Jing Liu ◽

Shengcai Chen ◽

Hao Wu ◽

Min Liu ◽

...

Keyword(s):

Nitrogen Fixation ◽

Genome Assembly ◽

Reference Genome ◽

De Novo ◽

Genomic Analysis ◽

Comparative Genomic ◽

High Quality ◽

Genome Wide ◽

A Genome ◽

Cultivated Soybean

Cultivated soybean (Glycine max) is an important source for protein and oil. Many elite cultivars with different traits have been developed for different conditions. Each soybean strain has its own genetic diversity, and the availability of more high-quality soybean genomes can enhance comparative genomic analysis for identifying genetic underpinnings for its unique traits. In this study, we constructed a high-quality de novo assembly of an elite soybean cultivar Jidou 17 (JD17) with chromsome contiguity and high accuracy. We annotated 52,840 gene models and reconstructed 74,054 high-quality full-length transcripts. We performed a genome-wide comparative analysis based on the reference genome of JD17 with three published soybeans (WM82, ZH13 and W05) , which identified five large inversions and two large translocations specific to JD17, 20,984 - 46,912 PAVs spanning 13.1 - 46.9 Mb in size, and 5 - 53 large PAV clusters larger than 500kb. 1,695,741 - 3,664,629 SNPs and 446,689 - 800,489 Indels were identified and annotated between JD17 and them. Symbiotic nitrogen fixation (SNF) genes were identified and the effects from these variants were further evaluated. It was found that the coding sequences of 9 nitrogen fixation-related genes were greatly affected. The high-quality genome assembly of JD17 can serve as a valuable reference for soybean functional genomics research.

Highly Contiguous Nanopore Genome Assembly of Chlamydomonas reinhardtii CC-1690

Microbiology Resource Announcements ◽

10.1128/mra.00726-20 ◽

2020 ◽

Vol 9 (37) ◽

Author(s):

Samuel O’Donnell ◽

Frederic Chaux ◽

Gilles Fischer

Keyword(s):

Chlamydomonas Reinhardtii ◽

Genome Size ◽

Genome Assembly ◽

Reference Genome ◽

De Novo ◽

Content Type ◽

Oxford Nanopore ◽

A Genome ◽

Reference Quality

ABSTRACT The current Chlamydomonas reinhardtii reference genome remains fragmented due to gaps stemming from large repetitive regions. To overcome the vast majority of these gaps, publicly available Oxford Nanopore Technology data were used to create a new reference-quality de novo genome assembly containing only 21 contigs, 30/34 telomeric ends, and a genome size of 111 Mb.

Recovery of non-reference sequences missing from the human reference genome

BMC Genomics ◽

10.1186/s12864-019-6107-1 ◽

2019 ◽

Vol 20 (1) ◽

Cited By ~ 3

Author(s):

Ran Li ◽

Xiaomeng Tian ◽

Peng Yang ◽

Yingzhi Fan ◽

Ming Li ◽

...

Keyword(s):

Human Genome ◽

Tandem Repeats ◽

Reference Genome ◽

De Novo ◽

Precise Location ◽

Protein Coding ◽

Human Reference Genome ◽

Mhc Haplotype ◽

Reference Sequences ◽

Flanking Regions

Abstract Background The non-reference sequences (NRS) represent structure variations in human genome with potential functional significance. However, besides the known insertions, it is currently unknown whether other types of structure variations with NRS exist. Results Here, we compared 31 human de novo assemblies with the current reference genome to identify the NRS and their location. We resolved the precise location of 6113 NRS adding up to 12.8 Mb. Besides 1571 insertions, we detected 3041 alternate alleles, which were defined as having less than 90% (or none) identity with the reference alleles. These alternate alleles overlapped with 1143 protein-coding genes including a putative novel MHC haplotype. Further, we demonstrated that the alternate alleles and their flanking regions had high content of tandem repeats, indicating that their origin was associated with tandem repeats. Conclusions Our study detected a large number of NRS including many alternate alleles which are previously uncharacterized. We suggested that the origin of alternate alleles was associated with tandem repeats. Our results enriched the spectrum of genetic variations in human genome.

Closing Human Reference Genome Gaps: Identifying and Characterizing Gap-Closing Sequences

G3 Genes|Genome|Genetics ◽

10.1534/g3.120.401280 ◽

2020 ◽

Vol 10 (8) ◽

pp. 2801-2809 ◽

Cited By ~ 1

Author(s):

Tingting Zhao ◽

Zhongqu Duan ◽

Georgi Z. Genchev ◽

Hui Lu

Keyword(s):

Reference Genome ◽

De Novo ◽

Sequence Length ◽

Sequencing Data ◽

Human Reference Genome ◽

Satellite Sequences ◽

Long Read ◽

Data Gap ◽

Simple Repeats ◽

Gap Closing

Despite continuous updates of the human reference genome, there are still hundreds of unresolved gaps which account for about 5% of the total sequence length. Given the availability of whole genome de novo assemblies, especially those derived from long-read sequencing data, gap-closing sequences can be determined. By comparing 17 de novo long-read sequencing assemblies with the human reference genome, we identified a total of 1,125 gap-closing sequences for 132 (16.9% of 783) gaps and added up to 2.2 Mb novel sequences to the human reference genome. More than 90% of the non-redundant sequences could be verified by unmapped reads from the Simons Genome Diversity Project dataset. In addition, 15.6% of the non-reference sequences were found in at least one of four non-human primate genomes. We further demonstrated that the non-redundant sequences had high content of simple repeats and satellite sequences. Moreover, 43 (32.6%) of the 132 closed gaps were shown to be polymorphic; such sequences may play an important biological role and can be useful in the investigation of human genetic diversity.

Minos: variant adjudication and joint genotyping of cohorts of bacterial genomes

10.1101/2021.09.15.460475 ◽

2021 ◽

Author(s):

Martin Hunt ◽

Brice Letcher ◽

Kerri M Malone ◽

Giang Nguyen ◽

Michael B Hall ◽

...

Keyword(s):

Current Knowledge ◽

Variant Calling ◽

Rifampicin Resistance ◽

Bacterial Genomes ◽

Single Nucleotide ◽

A Genome ◽

Bacterial Genomics ◽

Single Nucleotide Polymorphism Variation ◽

Reference Genomes ◽

Genome Graph

Short-read variant calling for bacterial genomics is a mature field, and there are many widely-used software tools. Different underlying approaches (eg pileup, local or global assembly, paired-read use, haplotype use) lend each tool different strengths, especially when considering non-SNP (single nucleotide polymorphism) variation or potentially distant reference genomes. It would therefore be valuable to be able to integrate the results from multiple variant callers, using a robust statistical approach to "adjudicate" at loci where there is disagreement between callers. To this end, we present a tool, Minos, for variant adjudication by mapping reads to a genome graph of variant calls. Minos allows users to combine output from multiple variant callers without loss of precision. Minos also addresses a second problem of joint genotyping SNPs and indels in bacterial cohorts, which can also be framed as an adjudication problem. We benchmark on 62 samples from 3 species (Mycobacterium tuberculosis, Staphylococcus aureus, Klebsiella pneumoniae) and an outbreak of 385 M. tuberculosis samples. Finally, we joint genotype a large M. tuberculosis cohort (N≈15k) for which the rifampicin phenotype is known. We build a map of non-synonymous variants in the RRDR (rifampicin resistance determining region) of the rpoB gene and extend current knowledge relating RRDR SNPs to heterogeneity in rifampicin resistance levels. We replicate this finding in a second M. tuberculosis cohort (N≈13k). Minos is released under the MIT license, available at https://github.com/iqbal-lab-org/minos.

Recovery of non-reference sequences missing from the human reference genome

10.21203/rs.2.11742/v2 ◽

2019 ◽

Author(s):

Ran Li ◽

Xiaomeng Tian ◽

Peng Yang ◽

Yingzhi Fan ◽

Ming Li ◽

...

Keyword(s):

Human Genome ◽

Tandem Repeats ◽

Reference Genome ◽

De Novo ◽

Precise Location ◽

Protein Coding ◽

Human Reference Genome ◽

Mhc Haplotype ◽

Reference Sequences ◽

Flanking Regions

Abstract Background The non-reference sequences (NRS) represent structure variations in human genome with potential functional significance. However, besides the known insertions, it is currently unknown whether other types of structure variations with NRS exist. Results Here, we compared 31 human de novo assemblies with the current reference genome to identify the NRS and their location. We resolved the precise location of 6,113 NRS adding up to 12.8 Mb. Besides 1,571 insertions, we detected 3,041 alternate alleles, which were defined as having less than 90% (or none) identity with the reference alleles. These alternate alleles overlapped with 1,143 protein-coding genes including a putative novel MHC haplotype. Further, we demonstrated that the alternate alleles and their flanking regions had high content of tandem repeats, indicating that their origin was associated with tandem repeats. Conclusions Our study detected a large number of NRS including many alternate alleles which are previously uncharacterized. We suggested that the origin of alternate alleles was associated with tandem repeats. Our results enriched the spectrum of genetic variations in human genome.

NovoGraph: Human genome graph construction from multiple long-read de novo assemblies

F1000Research ◽

10.12688/f1000research.15895.2 ◽

2018 ◽

Vol 7 ◽

pp. 1391

Author(s):

Evan Biederstedt ◽

Jeffrey C. Oliver ◽

Nancy F. Hansen ◽

Aarti Jajoo ◽

Nathan Dunn ◽

...

Keyword(s):

Human Genome ◽

De Novo ◽

Wide Spectrum ◽

Third Party ◽

Sequencing Data ◽

Multiple Sequence ◽

Human Genomes ◽

A Genome ◽

Long Read ◽

Genome Graph

Genome graphs are emerging as an important novel approach to the analysis of high-throughput human sequencing data. By explicitly representing genetic variants and alternative haplotypes in a mappable data structure, they can enable the improved analysis of structurally variable and hyperpolymorphic regions of the genome. In most existing approaches, graphs are constructed from variant call sets derived from short-read sequencing. As long-read sequencing becomes more cost-effective and enables de novo assembly for increasing numbers of whole genomes, a method for the direct construction of a genome graph from sets of assembled human genomes would be desirable. Such assembly-based genome graphs would encompass the wide spectrum of genetic variation accessible to long-read-based de novo assembly, including large structural variants and divergent haplotypes. Here we present NovoGraph, a method for the construction of a human genome graph directly from a set of de novo assemblies. NovoGraph constructs a genome-wide multiple sequence alignment of all input contigs and creates a graph by merging the input sequences at positions that are both homologous and sequence-identical. NovoGraph outputs resulting graphs in VCF format that can be loaded into third-party genome graph toolkits. To demonstrate NovoGraph, we construct a genome graph with 23,478,835 variant sites and 30,582,795 variant alleles from de novo assemblies of seven ethnically diverse human genomes (AK1, CHM1, CHM13, HG003, HG004, HX1, NA19240). Initial evaluations show that mapping against the constructed graph reduces the average mismatch rate of reads from sample NA12878 by approximately 0.2%, albeit at a slightly increased rate of reads that remain unmapped.

Recovery of non-reference sequences missing from the human reference genome

10.21203/rs.2.11742/v1 ◽

2019 ◽

Author(s):

Ran Li ◽

Xiaomeng Tian ◽

Peng Yang ◽

Yingzhi Fan ◽

Ming Li ◽

...

Keyword(s):

Tandem Repeats ◽

Reference Genome ◽

De Novo ◽

Precise Location ◽

Protein Coding ◽

Human Reference Genome ◽

Protein Coding Genes ◽

Mhc Haplotype ◽

Reference Sequences ◽

Flanking Regions

Abstract The non-reference sequences (NRS) represent structure variations in human genome with potential functional significance. However, besides the known insertions, it is currently unknown whether other types of structure variations with NRS exist. Here, we compared 31 human de novo assemblies with the current reference genome to identify the NRS and their location. We resolved the precise location of 6,113 NRS adding up to 12.8 Mb. Besides 1,571 insertions, we detected 3,041 alternate alleles, which were defined as having less than 90% (or none) identity with the reference alleles. These alternate alleles overlapped with 1,143 protein-coding genes including a putative novel MHC haplotype. Further, we demonstrated that the alternate alleles and their flanking regions had high content of tandem repeats, indicating that their origin was associated with tandem repeats. Our study enriched the spectrum of human genetic variations.