While the identification of individual SNPs has been readily available for some time, the ability to accurately phase SNPs and structural variation across a haplotype has been a challenge. With individual reads of an average length of 9 kb (P5-C3), and individual reads beyond 30 kb in length, SMRT Sequencing technology allows the identification of mutation combinations such as microdeletions, insertions, and substitutions without any predetermined reference sequence. Long- amplicon analysis is a novel protocol that identifies and reports the abundance of differing clusters of sequencing reads within a single library. Graphs generated via hierarchical clustering of individual sequencing reads…
Third generation single molecule sequencing technology from Pacific Biosciences, Moleculo, Oxford Nanopore, and other companies are revolutionizing genomics by enabling the sequencing of long, individual molecules of DNA and RNA. One major advantage of these technologies over current short read sequencing is the ability to sequence much longer molecules, thousands or tens of thousands of nucleotides instead of mere hundreds. This capacity gives researchers substantially greater power to probe into microbial, plant, and animal genomes, but it remains unknown on how to best use these data. To answer this, we systematically evaluated the human genome and 25 other important genomes…
Second-generation sequencing has brought about tremendous insights into the genetic underpinnings of biology. However, there are many functionally important and medically relevant regions of genomes that are currently difficult or impossible to sequence, resulting in incomplete and fragmented views of genomes. Two main causes are (i) limitations to read DNA of extreme sequence content (GC-rich or AT-rich regions, low complexity sequence contexts) and (ii) insufficient read lengths which leave various forms of structural variation unresolved and result in mapping ambiguities.
2015 SMRT Informatics Developers Conference Presentation Slides: Ali Bashir of Mount Sinai School of Medicine discussed methods for characterizing structural variation in human genomes across a variety of coverage levels.
The free-living flatworm, Macrostomum lignano, much like its better known planarian relative, Schmidtea mediterranea, has an impressive regenerative capacity. Following injury, this species has the ability to regenerate almost an entirely new organism. This is attributable to the presence of an abundant somatic stem cell population, the neoblasts. These cells are also essential for the ongoing maintenance of most tissues, as their loss leads to irreversible degeneration of the animal. This set of unique properties makes a subset of flatworms attractive organisms for studying the evolution of pathways involved in tissue self-renewal, cell fate specification, and regeneration. The use of…
Sequence-based estimation of genetic diversity of Plasmodium falciparum, the most lethal malarial parasite, has proved challenging due to a lack of a complete genomic assembly. The skewed AT-richness (~80.6% (A+T)) of its genome and the lack of technology to assemble highly polymorphic sub-telomeric regions that contain clonally variant, multigene virulence families (i.e. var and rifin) have confounded attempts using short-read NGS technologies. Using single molecule, real-time (SMRT) sequencing, we successfully compiled all 14 nuclear chromosomes of the P. falciparum genome from telomere-to-telomere in single contigs. Specifically, amplification-free sequencing generated reads of average length 12 kb, with =50% of the reads…
Each human genome has thousands of structural variants compared to the reference assembly, up to 85% of which are difficult or impossible to detect with Illumina short reads and are only visible with long, multi-kilobase reads. The PacBio RS II and Sequel single molecule, real-time (SMRT) sequencing platforms have made it practical to generate long reads at high throughput. These platforms enable the discovery of structural variants just as short-read platforms did for single nucleotide variants. Numerous software algorithms call structural variants effectively from PacBio long reads, but algorithm sensitivity is lower for insertion variants and all heterozygous variants. Furthermore,…
Despite amazing progress over the past quarter century in the technology to detect genetic variants, intermediate-sized structural variants (50 bp to 50 kb) have remained difficult to identify. Such variants are too small to detect with array comparative genomic hybridization, but too large to reliably discover with short-read DNA sequencing. Recent de novo assemblies of human genomes have demonstrated the power of PacBio Single Molecule, Real-Time (SMRT) Sequencing to fill this technology gap and sensitively identify structural variants in the human genome. While de novo assembly is the ideal method to identify variants in a genome, it requires high depth…
Though a role for structural variants in human disease has long been recognized, it has remained difficult to identify intermediate-sized variants (50 bp to 5 kb), which are too small to detect with array comparative genomic hybridization, but too large to reliably discover with short-read DNA sequencing. Recent studies have demonstrated that PacBio Single Molecule, Real-Time (SMRT) sequencing fills this technology gap. SMRT sequencing detects tens of thousands of structural variants in the human genome, approximately five times the sensitivity of short-read DNA sequencing.
Structural variants (genomic differences =50 base pairs) contribute to the evolution of organisms traits and human disease. Most structural variants (SVs) are too small to detect with array comparative genomic hybridization but too large to reliably discover with short-read DNA sequencing. Recent studies in human genomes show that PacBio SMRT Sequencing sensitively detects structural variants.
The kakapo (Strigops habroptila) is a large, flightless parrot endemic to New Zealand. It is highly endangered with only ~150 individuals remaining, and intensive conservation efforts are underway to save this iconic species from extinction. These include genetic studies to understand critical genes relevant to fertility, adaptation and disease resistance, and genetic diversity across the remaining population for future breeding program decisions. To aid with these efforts, we have generated a high-quality de novo genome assembly using PacBio long-read sequencing. Using the new diploid-aware FALCON-Unzip assembler, the resulting genome of 1.06 Gb has a contig N50 of 5.6 Mb (largest…
Structural variants (SVs) – genomic differences =50 base pairs – are few by count compared to single nucleotide variants (SNVs) and indels but include most of the base pairs that differ between two humans.
Fast and effective variant calling algorithms have been crucial to the successful application of DNA sequencing in human genetics. In particular, joint calling – in which reads from multiple individuals are pooled to increase power for shared variants – is an important tool for population surveys of variation. Joint calling was applied by the 1000 Genomes Project to identify variants across many individuals each sequenced to low coverage (about 5-fold). This approach successfully found common small variants, but broadly missed structural variants and large indels for which short-read sequencing has limited sensitivity. To support use of large variants in rare…
Genomics studies have shown that the insertions, deletions, duplications, translocations, inversions, and tandem repeat expansions in the structural variant (SV) size range (>50 bp) contribute to the evolution of traits and often have significant associations with agronomically important phenotypes. However, most SVs are too small to detect with array comparative genomic hybridization and too large to reliably discover with short-read DNA sequencing. While de novo assembly is the most comprehensive way to identify variants in a genome, recent studies in human genomes show that PacBio SMRT Sequencing sensitively detects structural variants at low coverage. Here we present SV characterization in…
Bipolar disorder (BD) is a phenotypically and genetically complex neurological disorder that affects 1% of the worldwide population. There is compelling evidence from family, twin and adoption studies supporting the involvement of a genetic predisposition with estimated heritability up to ~ 80%. The risk in first-degree relatives is ten times higher than in the general population. Linkage and association studies have implicated multiple putative chromosomal loci for BD susceptibility, however no disease genes have yet to be identified. Here, we have fully characterized a ~12 Mb significantly linked (lod score=3.54) genomic region on chromosome Xq24-q27 in an extended family from…