31
votes
Accepted
Why do some assemblers require an odd-length kmer for the construction of de Bruijn graphs?
From the manual of Velvet:
it must be an odd number, to avoid palindromes. If you put in an even
number, Velvet will just decrement it and proceed.
the palindromes in biology are defined as ...
- 5,632
14
votes
Why do some assemblers require an odd-length kmer for the construction of de Bruijn graphs?
To expand on the answer above, in case it isn't clear, we show:
Why palindromic sequences must be even in length
Why palindromic sequences induce self-loops in a de Bruijn graph
Why self loops in a ...
- 243
8
votes
How to get fasta alignment file from SAM/BAM file?
I am not sure what you mean by "fasta alignment file". If you mean a multi-sequence alignment (MSA) in the fasta format, you can't get that because SAM keeps pairwise alignments only and doesn't align ...
- 6,575
7
votes
How to make a distinction between the "classical" de Bruijn graph and the one described in NGS papers?
Several papers have made this distinction, and a few indeed use different terms to distinguish between them. For example, Kazaux et al. (2016) acknowledge that:
These constraints favour the use of ...
- 669
7
votes
Accepted
How can I improve a long-read assembly with a repetitive genome?
"A few" 100kb reads won't help much. You need to apply the ultra-long protocol, which is different from the standard protocol.
You can't resolve 20kb near identical repeats/segdups with 10kb ...
- 6,575
6
votes
Accepted
Cufflinks Error: sort order of reads in BAMs must be the same
Just add --dta-cufflinks to your Hisat2 command, so that the output alignment file provides the attributes needed by Cufflinks (XS flags). This should do the job.
...
- 2,706
6
votes
Accepted
Is there a standard definition for "assembly polishing"?
In long-read assembly, "polish" refers to the step to improve the base accuracy of contig sequences. I believe the terminology was originated from the HGAP paper:
The final consensus–calling ...
- 6,575
5
votes
Reordering scaffolds according to a reference without a genetic map
Have you tried Mauve alignment? Its pretty easy once you become familiar and has a GUI for further ease of use. Additionally there are a few online tutorials on how to re-order contigs/ scaffolds ...
- 965
5
votes
Is there a standard definition for "assembly polishing"?
Disclaimer, this answer is based on feeling I got from talks and papers, but I do not have any hard reference supporting it.
I believe that genome polishing is a technique that was introduced for ...
- 5,632
5
votes
Accepted
estimate genome size: kmer-based approach from PacBio reads
I don't think there is a method that would estimate a genome size using raw long reads.
The genome size estimates based on raw reads are done by fitting a model to kmer spectra (for instance ...
- 5,632
5
votes
Accepted
Authoritative source on human cytogenetic regions?
Do you mean cytoband coordinates? For the human genome you can find them for example at UCSC.
hgdownload.cse.ucsc.edu/goldenPath/hg38/database/cytoBand.txt.gz
- 3,591
5
votes
Accepted
PacBio long-reads impact in transcriptome de novo assembly?
A few comments:
Never use N50 as a metric especially for transcriptomes. It has some semblance of relevance for genome assembly, but all that is void for a transcriptome with inherently dynamic ...
5
votes
Contamination on genome assembly
This could be organism-specific. We don't have a lot of info so far, so I would check a few more things:
Run something like FRC_align. Check if there's a clear signal between regions flagged as ...
5
votes
Accepted
How to solve Nextflow error: "Trace file already exists"?
Rotation of report files (trace, execution, timeline etc) was removed recently (since version 22.10.0 in a762ed5). To overwrite the existing trace file you will ...
- 3,148
4
votes
Accepted
How to calculate overall reference coverage with MUMmer?
I believe all you need to do is to run dnadiff from MUMmer. That will run a comparison and output a number of useful metrics.
- 156
4
votes
How to make a distinction between the "classical" de Bruijn graph and the one described in NGS papers?
In addition to the regular De Bruijn graph as depicted on the wikipedia, some implementations in bioinformatics feature additional processing. I guess the main reason figure 1 in the paper you linked (...
- 445
4
votes
Accepted
Improve a reference genome with sequencing data
Depending on the coverage of your data and the complexity of the genome, you could either reassemble the genome de novo or run a reference guided (or reference assisted) assembly. It sounds like you'...
- 5,090
4
votes
Improve a reference genome with sequencing data
One approach to this is to use whatever data you have to iteratively update the reference genome. You can keep chain files along the way so you can convert coordinates (e.g. in gff files) from the ...
- 972
4
votes
How to deal with heterozygosity during polishing of genome assembly based on long reads?
A few possibilities:
Falcon
Try falcon and falcon-unzip. These are designed exactly for your problem and your data: https://github.com/PacificBiosciences/FALCON
Not Falcon
If you think you have ...
- 972
4
votes
Accepted
Why can using more reads lead to a lower quality assembly?
The more reads you add the more errors you add into the assembly. This is because additional duplicate reads don't add nodes/edges to the de Bruijn graph, but those with errors do. By preselecting ...
- 19.8k
4
votes
Accepted
Why isn't there a standard method to convert GFA to JSON?
Short answer: no, there isn't a "standard" method, and there won't be.
Long answer: like TAB-delimited and XML, JSON alone is not a specific format. You have to define a schema to give meanings to ...
- 6,575
4
votes
Accepted
Separation of mixed plasmid DNA sequences post whole-plasmid sequencing
You would expect to have high coverage, given the plasmids are short, so de novo assembly would be likely very easy. Given that each plasmid is present in different multiples, you would expect ...
- 1,012
4
votes
Viral genome assembly using broad viral ngs pipeline?
Since you are already using the Broad Tools sets you can use Picard FastqToSam to make the conversion
As far a clipDb I am unfamiliar with that and a quick google search and look at the trimmomatic ...
- 2,584
4
votes
Difference between genome assembly and genome sequence alignment to a reference to find structural variants
the first being what the 1KGP and SDGP did and sequence the whole
genome, align the reads to the reference genome and end up with a BAM
file.
If you have a well defined reference genome (e.g. human, ...
- 3,958
4
votes
Accepted
Genome assembly of SRR12196449 with SPAdes
Update 2:
I looked into this a little more, with the various data sources.
This is related in part to the answer submitted by OP juanjo75es, in addition to discussion on chat. I don't entirely ...
- 4,212
4
votes
Accepted
Difference between paired-end, mate-pair and long read
They are all very different in separate regards, but they all refer to different wet-lab and sequencing protocols/technologies.
First, PE (paired end) reads are typically short (50-300) reads, most ...
4
votes
Accepted
Extract sequence context of high-degree nodes in assembly graphs
I don't have a recommendation of specific tools, but we might be able to use the GFA file itself to get at this with just bash commands.
For these examples I use the linked GFA here, which is a ...
- 4,212
4
votes
How to display novel genome assemblies or uncommon genome assemblies using the UCSC Genome Browser?
I found two methods:
You want to visit this page for instructions for novel assemblies: http://genomewiki.ucsc.edu/index.php/Assembly_Hubs .
However, before doing that I highly recommend that you ...
- 636
4
votes
Accepted
Velvet Optimizer automatically changes to hash-length 31
If a value for MAXKMERLENGTH was not set when compiling velveth, VelvetOptimizer just uses the default ...
- 3,148
3
votes
Difference between de novo transcriptome assembly methods
It's really a misnomer to call StringTie's non-reference based mode 'de-novo.' It's still using the reference genome sequence to guide the transcript assembly, it's just not using the reference ...
- 1,816
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