Questions tagged [sequence-alignment]

A computational technique to compare two nucleotide or protein sequences. There are two basic types of sequence alignment i.e. local alignment (local comparison of subsequences) or global alignment (end to end comparison of the entire sequences).

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483 views

What tool to use to map reads (samtools, sequencher,...)?

I am a beginner in Bioinformatics. I have 4 files: 2 fastq files (aln1.fastq and aln2.fastq) 2 bam files (aln.bam and aln.bam.bai) I know that: the raw file is aligned to hg19 human genome. The ...
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Question about SAM CIGAR string

My question is about the CIGAR specification. The documentation states: M 0 alignment match (can be a sequence match or mismatch) ...
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How to search for a protein sequence of an specific taxa in NCBI?

My example: Sequence of HBB (Hemoglobin Beta) in Fishes. How can I do a good search to obtain above sequences in NCBI? (I know hot to download them into a FASTA file)
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Do the BLAST scores have any relation between them?

Is there any relation among the BLAST scores (E-value, similarity, identity, gap, bit score)? Is the e-value score for an alignment proportional to other scores, such as similarity score (i.e. the ...
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171 views

How is the probability of a sequence occuring with BLAST calculated?

What is the probability that a given nucleotide/amino acid sequence will occur in the whole database program BLAST searches in? How this probability is calculated?
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Blosum matrix computation with X%

Why does the answers to the problem found in the referenced pdf, differ from my calculation below? I am trying to understand the math from this pdf from an online tutorial I am reading and my own math ...
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1answer
67 views

In DNA sequencing, is "mate pairs" synonymous with "paired ends"? If not, how do they differ?

By just looking at Roach et al's paper I get the impression that they are the same thing, and the Wikipedia URL for the former is a redirect to the latter. However, I suspect they are not exactly the ...
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150 views

How is output of DNA assembler measured?

I developed own DNA assembly pipeline. Input is set of reads and output is set of contigs. Many papers measure own algorithms and compare it against each other. There are basic metrics like: N50, N70....
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276 views

How to Determine the Most Conserved Sequence from BLAST Result?

I used BLAST to find the best aligned DNA sequence to my query sequence. The BLAST result shows a number of sequences that it calculated to be the best aligned sequences to the query sequence that I ...
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129 views

How do I run each individual record in a multi-fasta file against a database using PSI-Blast?

I'm new to standalone blast+ and the linux terminal. I set the bash-profile to load the PATH and BLASTDB for my blast already, but I don't know how to use psi-blast yet. How can I do the search ...
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What is the difference between sequence alignment and sequence assembly?

I read the wikipedia page about sequence alignment and sequence assembly but I have not been able to find any difference between the two. What is the difference between sequence alignment and sequence ...
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How to do multiple sequence alignment?

I have a DNA sequence that makes protein 1. but now I have asked to: compare the amino acid sequence of protein 1 with nine homologous proteins and make a multi sequence alignment (MSA) of the ...
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Do the bacterial species X, Y, Z code for proteins A, B, C?

My PI has assigned me a task to gather evidence to determine whether or not a list of particular species of Campylobacter and Helicobacter code for a list of several proteins. To put it simply I’ve ...
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607 views

blastn: What substitution matrix is used?

I'm currently working aligning sequences, and I need to compute similarity between pairs of DNA 'words' of a particular length. For amino acids I am able to use the substitution matrices in Biopython ...
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327 views

Determining the percentage of the query of an alignment from a BLAST output

Given this BLAST output, how can I determine the percentage of the query sequence in the alignment? I know that it's also referred to as 'query cover' but I can't seem to find anything online that ...
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How to get only perfect matches with blastn? [closed]

I have installed Blast locally and I've configured the nucleotide database to use. I want to search some sequences (from a .fastafile) in this genome. So I used blastn: ...
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How can I align more than 2 sequences locally?

ClustalW and Omega of EBI and Blast of NCBI, both globally align sequences. Smith waterman of EBI aligns sequences locally, but works with just two sequences. How can I align more than 2 sequences ...
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EMBOSS matcher and supermatcher - incongruent results?

I am trying to align a sequence to the mouse genome. I know a priori that part of my sequence should align to chromosome 9, but not all of it. I gathered that EMBOSS' ...
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What is the meaning of dots and dashes in clustalw?

I am converting outputs in stockholm format to clustalw using ...
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107 views

Is using Hidden Markov Models to find homologues sensible in abstract, short sequences?

HMM alignment tools like hhpred excel at finding subtle homologues of folded proteins that simpler scoring techniques (such those used in BLAST algorithms) would miss. I am only looking at a small (...
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800 views

How to do whole genome sequence alignment in R or Ruby/C++, any good language? [closed]

I need to perform tuberculosis mutation analysis. First step I need to do is to align sequences in fasta format against one reference file. i tried CLC genomics workstation --- it hangs on 60 000 ...
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233 views

Whole genome sequence analysis software

Please help to choose Bioconductor R packages and other software for the whole genome sequence data analysis and, in particlular, the goals of false discovery mutation rate, mutations exclusion, ...
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Aligning multiple sequences in heterogeneous group

I have a list of ~200 DNA sequences, representing probably 50 different genomic regions but they're all mixed up. For example, if I have seq1, seq2.... seq10, ...
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Bowtie: cannot read fasta file?

I am trying to use bowtie2 to analyze my data in FASTA format, but it seems that this version can't read properly my data. My command line is as follows: ...
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365 views

Where to find the corrected BLOSUM matrices?

I was looking at this paper which talks about the miscalculations in the BLOSUM matrices and how the "wrong" BLOSUM62 matrix performs better than the corrected version. I was trying to find the ...
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97 views

Applying Constraint Programming to sequence alignment/analysis

My Masters program is focused on formal methods such as SAT solving and constraint programming. I am interested in applying such techniques to problems in sequence alignment and sequence analysis, ...
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86 views

How is the GenBank used in typical biological research? [closed]

How is the GenBank used in typical biological research? According to the GenBank statistics, the database contains about 100 million sequences. I find it difficult to understand why is all that data ...
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1answer
200 views

Datasets of aligned nucleotide sequences [closed]

Where can I find some datasets of aligned nucleotide sequences? And what should I assume about the accuracy of the alignments there? (I would like to use such datasets for training the alignment ...
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687 views

Standard datasets for testing new multiple sequence alignment algorithms?

Are there any open and freely distributed standard datasets for testing new algorithms for multiple sequence alignment?
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641 views

What is the state-of-the-art algorithm for multiple sequence alignment?

Which algorithm or algorithms are considered the standard or state-of-the-art for multiple sequence alignment? How big is the need for better algorithms? How many sequences need to be alignment in a ...
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What E-value BLAST cut-off is best?

What is the best cut-off for e-value in BLAST? Some say 0.01 ,others 0.0001? Even BLAST tutorials don't give a very clear idea about which cutoff suits which purpose? Could some experts give me a ...
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1answer
750 views

Blosum matrix with probabilities instead of the positive and negative scores

I am trying to find a version of the BLOSUM matrix that has the frequencies instead of the scaled log-odds. i.e. instead of the common version that tells us that the score LEU/ASP is -4, I would like ...
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1answer
170 views

Converting Ensembl Compara gene tree DNA alignment to corresponding amino acid alignment

I have Ensembl compara gene tree alignments (Compara.gene_trees.57.fasta.gz downloaded from ftp://ftp.ensembl.org/pub/release-57/emf/ensembl-compara/homologies/) in nucleotide format. According to ...
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181 views

Sequence alignment scoring

The following table is from Deonier's text Computational Gene Analysis at p. 152. This is an exercise in global sequence alignment and scoring of alternative sequences. The text proposed a solution (...
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2k views

What is happening in each iteration of PSI-BLAST?

I understand that the first BLAST yields almost the same results as blastp. The second time the iterated blast generates different results as it uses different matrix based on our first result. But I ...
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1answer
740 views

Codon alignment via Python? [closed]

I have pairs of coding DNA sequences which I wish to perform pairwise codon alignments via Python, I have "half completed" the process. So far.. I retrive pairs of orthologous DNA sequences from ...
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577 views

what does sequences overlap indicate

what does it mean if different protein sequences overlap upon multiple alignment, are they the same, do they have a common ancestor, are they recombinants of each other and how does one go on to ...
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What is the difference between local and global sequence alignments?

There are a bunch of different alignment tools out there, and I don't want to get bogged down in the maths behind them as this not only between software but varies from software version to version. ...

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