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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17 views

Calculating sequence divergence score for a protein from identity or similarity score?

I have % identity and % similarity scores for ~50K protein alignments, that I fetched from Ensembl Compara database. The issue ...
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85 views

What does genetically tractable strain mean?

I want to study the properties of Pyrococcus Furiosus in surving to gamma irradiation by exploiting the analysis of DNA sequencing data as a bioinformatics study. Before learning how to analyse this ...
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1answer
42 views

Using BLAST for molecular replacement in structural biology

This is my first time trying to do molecular replacement to solve a protein structure. I am using the NCBI blastp program to find suitable search models. When choosing a search model, I understand ...
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41 views

Expected number of mismatches between two alleles of a gene in a population?

I can't find any article about the expected number of mismatches in alignment of two alleles of an assumed gene. Any reference or information about allele mismatch ratio (in a species or higher taxa) ...
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61 views

How to reduce the number of sequences in a Multiple Sequence Alignment?

I have a Multiple Sequence Alignment, where there are around 5000 sequences. There also exists many sequences where, there are so much of non-sequenced regions (for instance, AU----CGGGCA--NNNNNNNNNN)....
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47 views

in order to align genome multi-fasta files, do you ignore the chromosome sections?

I want to test my implementation of Needleman-Wunsch on two fasta files downloaded from https://hgdownload.soe.ucsc.edu/. However, fasta files on this site are multi-fasta and therefore are split into ...
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1answer
48 views

Why do I get cytosine to guanine/adenine transitions in bisulphite treated sequences?

I got my sequencing results (bisulphite treated and non treated sequences of same species Allium cepa) and now I have to do analysis in Cymate online tool. I prepared all sequences as it is written in ...
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1answer
34 views

Available Protein sequence alignment dataset and HMM model

I am new to biology and I find my algorithm may be used in the Protein sequence alignment, since it is a henced HMM model. I find that people use HMM to generate noisy copies of the consensus sequence ...
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61 views

Different BLOSUM matrices [duplicate]

What is the difference between different variants of BLOSUM matrices? e.g What is the difference between BLOSUM 30 and BLOSUM 62?
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6k views

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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1answer
93 views

Webtool to design guide RNA (gRNA) for use with CRISPR-AsCpf1?

My goals are to use a free webtool to: Identify guide RNAs (direct-repeat sequence followed by the targeting sequence) appropriate for use with AsCpf1 in order to target a specific segment of genomic ...
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176 views

What tool can I use to align multiple protein sequences to one reference sequence?

I have a protein of interest which is ~300 amino acids in length. I also have around 40 short sequences (all 9 amino acids in length); these are all very different from each other. I would like to ...
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857 views

What is the relationship between the e value reported by HMMER and BLAST? (Are they equivalent?)

Both HMMER and BLAST report an e value for alignments. Is it calculated in the same way and - assuming that default settings are used - can they be compared directly (are the equivalent)? If not ...
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303 views

How to interpret different results from Clustal Omega and Multalin?

I have been working on aptamers, which are nucleotide sequences. They bind to various targets, in my case a particular cell surface receptor. The people associated with the project performed SELEX and ...
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1answer
56 views

How evolutionarily conserved are UTRs?

Coding sequences of genes have a certain degree of evolutionary conservation, so that comparisons based on sequences (BLAST, HMMER etc) can be informative. Generally speaking, the more two species are ...
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42 views

Which database has the ready made 16S rRNA Multiple Sequence Alignment File that I can download directly from?

In my case, I need the ready made 16S rRNA Multiple Sequence Alignment File for E.coli and use it to generate the phylogenetic tree file in Newick format. I've tried using the one from utexas website, ...
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693 views

Details of Needleman–Wunsch algorithm

I try to understand details of the Needleman–Wunsch algorithm and use an example from the book [Nello Cristianini, Matthew W. Hahn. Introduction to Computational Genomics. A Case Studies Approach, www....
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85k views

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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1answer
49 views

Sequencing inaccurate at the primer site

The times I have sent a sample to sequence, both the forward and the reverse primer sites, show high inaccuracy while the rest of the gene is correctly sequenced. Because of this, the sequences of my ...
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90 views

Consensus symbols in multiple sequence alignment [closed]

I was using multAlin for multiple aligning a set of sequences. The output I and came across included the following documentation (English corrected): Consensus symbols: ! is any of IV $ is any ...
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1answer
3k views

Why does BLAST reduce word size for short proteins?

I'm using BLAST to identify a short protein (BLASTp). If I check the short query then the word size reduces from 3 to 2. However the search will then be less ...
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1answer
46 views

Confusion about a gene's description

I have a very basic biology question. I am reading the description of gene FAM166A here, and I have no idea what "sequence similarity 166" means. What does 166 stand for, what is this gene's sequence "...
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15k views

How to convert bwa mem output to BAM format without saving SAM file

I want to go straight from bwa mem alignment to BAM format as I don't need the SAM file and it takes up too much space. How do I achieve this?
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377 views

Designing degenerate primers using alignment of protein sequences from other species

I am trying to design a PCR primer for a gene whose sequence is not known. Even the whole transcriptome sequencing done in our lab did not identify that particular gene. Hence, I guess I am left with ...
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1answer
436 views

How to pipe Bwa-mem output without saving SAM file

I'm trying to find circular ARN using the program CIRI2. CIRI2 takes as input SAM file from BWA-mem, but I would like to go straight to CIRI2 output without saving SAM file. Is there a way to achieve ...
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5answers
33k views

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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336 views

What is the best alignment definition for the Multiple Sequence Alignment (MSA) problem?

For simplicity, suppose that I am penalising mismatches and gaps with -1 and adding a score +100 for each match. Does the optimum alignment of the three DNA sequences ...
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8k views

What is the meaning of “E-value” in the BLAST search?

After reading many pages, I still do not understand the definition. Can someone use simple words to explain me that? https://en.wikipedia.org/wiki/BLAST This expectation or expect value "E" (often ...
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2answers
510 views

What does chrUn mean in the output from a Bowtie run on human sequences?

After having performed an alignment using bowtie2 and GRCh38 as a reference sequence, I got inusual matches on chrUn. Here a small part of the SAM file: ...
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236 views

What is the difference between contig- and read-based sequence alignment?

I am trying to understand the difference between read based and contig based alignment. Is contig based alignment refer to de novo assembly and then it is align to a reference genome. I am confused ...
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1answer
432 views

Identity and similarity for Multiple Sequence Alignment (MSA) of proteins

I have to do homology modeling for a transmembrane protein (sodium channel) and right now I am in the process of aligning the sequences of the template with the homologous proteins I have found. I am ...
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2answers
407 views

How to detect Single Nucleotide Variants (SNVs)?

This image is obtained from this paper. The description of this image is as follows:- DNA-sequence reads from a tumor sample are aligned to a reference genome (shown in gray). Single-nucleotide ...
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329 views

Is setting high mismatch and gap penalties sufficient to distinguish perfectly mapping reads?

I have a fat pile of 125bp whole genome shotgun reads that have undergone quality control, and I would like to pull out just those reads that do not map perfectly to the genome. When I set extremely ...
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278 views

Difference of coverage between amplicons

I have 2 fastq files and I generated BAM file (indexed and sorted) of some reads. I aligned them to a reference genome (hg19). I am working with different primers. ...
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1answer
1k views

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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1answer
671 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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10k views

How to interpret Percent identity matrix created by Clustal Omega?

I did a multiple sequence alignment using Clustal omega. checked similarity for 3 protein sequences : aspartyl aminopeptidase [Homo sapiens], aminopeptidase P (APP) [Plasmodium falciparum 3D7], yeast ...
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38 views

Creating BLAST database with nucleotide “place holder”

I have a set of nucleotide sequences that contain some special characters with multiple meanings: H -> C, A or T K -> G or T M -> C or A R -> G or A S -> C or G W -> A or T Y -> c or T I would like ...
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56 views

Are there any examples of weighted edit distance genome alignments?

It has been said that weighted edit distance is a preferred way to compare/align genomes in practice, e.g., when identifying genetically similar patients. I wonder if there are some concrete examples ...
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69 views

What factors should I consider when selecting a reference genome for mapping?

I am under the impression that the most recent reference genome is typically the best case. What other things should I consider when selecting a reference genome? For example, is there any particular ...
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2answers
506 views

What is a good multiple alignment of large genome sequences when working with limited hardware?

I need to align bacterial genomes (namely mycobacteria, over 4 Mb in length), and my choice would have been either 'muscle' or 'clustalW'; however these algorithms are too memory demanding for such ...
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66 views

Phylogenetic tree with tagging

I'm working for a software company. For one of our projects, we need software to cluster nodes in a phylogenetic tree by a certain kind of similarity and give them a user-defined tag. Preferably, the ...
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3answers
735 views

Do all multiple sequence alignments employ global alignment algorithms?

Multiple sequence alignments are usually done between sequences of similar length, which resembles best a global alignment. However, I'm not sure at all what the algorithmic background would be in ...
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Finding diploid neanderthal alignment data, looking for ambiguity codes

I'm using Neanderthal alignment data from here: http://www.eva.mpg.de/neandertal/draft-neandertal-genome/data.html Specifically, the .bam files. I would like to find alignments for neanderthal ...
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2answers
345 views

How to compare Smith–Waterman algorithm implementations?

Assume that you have two implementations of the Smith–Waterman algorithm (with what ever heuristic they apply to speed up) for local sequence alignment of genomic sequences. I would like to know if ...
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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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3answers
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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How does one apply Bayesian inference to quantify a read the deeper you sequence?

For NGS sequencing technology, the "deeper" you sequence given fragments, the more certain you are of what is being sequenced. This sounds like a simple application of Bayes's Rule. What is the ...
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598 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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164 views

why does the score matrix influence the E value (BLAST)

When I align two HBB protein sequences wich have 80% identity, I used two kind of score matrices: Blosum62 and PAM30, to figure out the impact on my results. I noticed that the bit score is higher ...