1,898 research outputs found
Hardness of Covering Alignment : Phase Transition in Post-Sequence Genomics
Covering alignment problems arise from recent developments in genomics; so called pan-genome graphs are replacing reference genomes, and advances in haplotyping enable full content of diploid genomes to be used as basis of sequence analysis. In this paper, we show that the computational complexity will change for natural extensions of alignments to pan-genome representations and to diploid genomes. More broadly, our approach can also be seen as a minimal extension of sequence alignment to labelled directed acyclic graphs (labeled DAGs). Namely, we show that finding a covering alignment of two labeled DAGs is NP-hard even on binary alphabets. A covering alignment asks for two paths R-1 (red) and G(1) (green) in DAG D-1 and two paths R-2 (red) and G(2) (green) in DAG D-2 that cover the nodes of the graphs and maximize the sum of the global alignment scores: asosp(R-1), sp(R-2)) + asosp(G(1)), sp(G(2))), where sp(P) is the concatenation of labels on the path P. Pair-wise alignment of haplotype sequences forming a diploid chromosome can be converted to a two-path coverable labelled DAG, and then the covering alignment models the similarity of two diploids over arbitrary recombinations. We also give a reduction to the other direction, to show that such a recombination-oblivious diploid alignment is NP-hard on alphabets of size 3.Peer reviewe
Genomic resource development for a diploid mint: Mentha longifolia
This research project aimed to develop genomic resources needed to enable construction of a genetic linkage map of the diploid mint species Mentha longifolia. Such a map would facilitate identification of plant genes involved in resistance to Verticillium fungal infection. For this purpose, a small genomic library was constructed from germplasm accession CMEN 585, 279 genomic inserts were sequenced and annotated and 19 PCR primer pairs were designed and tested on two resistant and two susceptible accessions. The Cleaved Modified Polymorphic Sequence (CAPS) method of molecular marker genotyping was found to detect little variation between crossing parents CMEN 585 (resistant) and CMEN 584 (susceptible). Comparative sequencing of PCR products from two European and two South African accessions revealed greater diversity between than within geographic locations. Future efforts should focus on assessing more sensitive genotyping methods, and developing a mapping population from a cross between European and South African accessions
Learning Character Strings via Mastermind Queries, with a Case Study Involving mtDNA
We study the degree to which a character string, , leaks details about
itself any time it engages in comparison protocols with a strings provided by a
querier, Bob, even if those protocols are cryptographically guaranteed to
produce no additional information other than the scores that assess the degree
to which matches strings offered by Bob. We show that such scenarios allow
Bob to play variants of the game of Mastermind with so as to learn the
complete identity of . We show that there are a number of efficient
implementations for Bob to employ in these Mastermind attacks, depending on
knowledge he has about the structure of , which show how quickly he can
determine . Indeed, we show that Bob can discover using a number of
rounds of test comparisons that is much smaller than the length of , under
reasonable assumptions regarding the types of scores that are returned by the
cryptographic protocols and whether he can use knowledge about the distribution
that comes from. We also provide the results of a case study we performed
on a database of mitochondrial DNA, showing the vulnerability of existing
real-world DNA data to the Mastermind attack.Comment: Full version of related paper appearing in IEEE Symposium on Security
and Privacy 2009, "The Mastermind Attack on Genomic Data." This version
corrects the proofs of what are now Theorems 2 and 4
Towards Better Understanding of Artifacts in Variant Calling from High-Coverage Samples
Motivation: Whole-genome high-coverage sequencing has been widely used for
personal and cancer genomics as well as in various research areas. However, in
the lack of an unbiased whole-genome truth set, the global error rate of
variant calls and the leading causal artifacts still remain unclear even given
the great efforts in the evaluation of variant calling methods.
Results: We made ten SNP and INDEL call sets with two read mappers and five
variant callers, both on a haploid human genome and a diploid genome at a
similar coverage. By investigating false heterozygous calls in the haploid
genome, we identified the erroneous realignment in low-complexity regions and
the incomplete reference genome with respect to the sample as the two major
sources of errors, which press for continued improvements in these two areas.
We estimated that the error rate of raw genotype calls is as high as 1 in
10-15kb, but the error rate of post-filtered calls is reduced to 1 in 100-200kb
without significant compromise on the sensitivity.
Availability: BWA-MEM alignment: http://bit.ly/1g8XqRt; Scripts:
https://github.com/lh3/varcmp; Additional data:
https://figshare.com/articles/Towards_better_understanding_of_artifacts_in_variating_calling_from_high_coverage_samples/981073Comment: Published versio
Next Generation Cluster Editing
This work aims at improving the quality of structural variant prediction from
the mapped reads of a sequenced genome. We suggest a new model based on cluster
editing in weighted graphs and introduce a new heuristic algorithm that allows
to solve this problem quickly and with a good approximation on the huge graphs
that arise from biological datasets
Next-generation VariationHunter: combinatorial algorithms for transposon insertion discovery
Recent years have witnessed an increase in research activity for the detection of structural variants (SVs) and their association to human disease. The advent of next-generation sequencing technologies make it possible to extend the scope of structural variation studies to a point previously unimaginable as exemplified by the 1000 Genomes Project. Although various computational methods have been described for the detection of SVs, no such algorithm is yet fully capable of discovering transposon insertions, a very important class of SVs to the study of human evolution and disease. In this article, we provide a complete and novel formulation to discover both loci and classes of transposons inserted into genomes sequenced with high-throughput sequencing technologies. In addition, we also present âconflict resolutionâ improvements to our earlier combinatorial SV detection algorithm (VariationHunter) by taking the diploid nature of the human genome into consideration. We test our algorithms with simulated data from the Venter genome (HuRef) and are able to discover >85% of transposon insertion events with precision of >90%. We also demonstrate that our conflict resolution algorithm (denoted as VariationHunter-CR) outperforms current state of the art (such as original VariationHunter, BreakDancer and MoDIL) algorithms when tested on the genome of the Yoruba African individual (NA18507)
Minimum error correction-based haplotype assembly: considerations for long read data
The single nucleotide polymorphism (SNP) is the most widely studied type of
genetic variation. A haplotype is defined as the sequence of alleles at SNP
sites on each haploid chromosome. Haplotype information is essential in
unravelling the genome-phenotype association. Haplotype assembly is a
well-known approach for reconstructing haplotypes, exploiting reads generated
by DNA sequencing devices. The Minimum Error Correction (MEC) metric is often
used for reconstruction of haplotypes from reads. However, problems with the
MEC metric have been reported. Here, we investigate the MEC approach to
demonstrate that it may result in incorrectly reconstructed haplotypes for
devices that produce error-prone long reads. Specifically, we evaluate this
approach for devices developed by Illumina, Pacific BioSciences and Oxford
Nanopore Technologies. We show that imprecise haplotypes may be reconstructed
with a lower MEC than that of the exact haplotype. The performance of MEC is
explored for different coverage levels and error rates of data. Our simulation
results reveal that in order to avoid incorrect MEC-based haplotypes, a
coverage of 25 is needed for reads generated by Pacific BioSciences RS systems.Comment: 17 pages, 6 figure
Detecting Transcriptomic Structural Variants in Heterogeneous Contexts via the Multiple Compatible Arrangements Problem
Transcriptomic structural variants (TSVs) - large-scale transcriptome sequence change due to structural variation - are common, especially in cancer. Detecting TSVs is a challenging computational problem. Sample heterogeneity (including differences between alleles in diploid organisms) is a critical confounding factor when identifying TSVs. To improve TSV detection in heterogeneous RNA-seq samples, we introduce the Multiple Compatible Arrangement Problem (MCAP), which seeks k genome rearrangements to maximize the number of reads that are concordant with at least one rearrangement. This directly models the situation of a heterogeneous or diploid sample. We prove that MCAP is NP-hard and provide a 1/4-approximation algorithm for k=1 and a 3/4-approximation algorithm for the diploid case (k=2) assuming an oracle for k=1. Combining these, we obtain a 3/16-approximation algorithm for MCAP when k=2 (without an oracle). We also present an integer linear programming formulation for general k. We characterize the graph structures that require k>1 to satisfy all edges and show such structures are prevalent in cancer samples. We evaluate our algorithms on 381 TCGA samples and 2 cancer cell lines and show improved performance compared to the state-of-the-art TSV-calling tool, SQUID
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