Question: How To Find The Locations Of A Short Specific Sequence In A Genome With 1 Or 2 Mismatches Allowed?
gravatar for William
5.1 years ago by
William4.3k wrote:

We have a 23 nucleotide CRISPR target sequence of which I would like to find out if it also present in other locations in the genome.

The sequences directs a CRISPR RNA construct to introduce a indel mutation in the genome and we would like to make sure that there is only one target loci. There is also one N in the nucleotide sequence.

Let's say the 23 nucleotide sequence is :


How do I find all the loci in a genome were this sequence matches, exactly (well 1 mismatch one the N), or with say an edit distance of 2 or 3?

I tried BWA aln with a short sequence of 23 bp from the human genome with parameters -l 23 -k 2 but it didn't find back the location of the 23 bp. Does bwa work with sequences of this lenght?

I tried blast but I get back a lot of results and I can't control the max edit distance.

sequence bwa blast • 3.2k views
ADD COMMENTlink modified 17 months ago by Biostar ♦♦ 20 • written 5.1 years ago by William4.3k

PatMatch allows controlling the number of mismatches and whether that includes insertions, deletions, and/or substitutions. There is a stand-alone version of the software available as posted about here in response to a related question. (In fact, at the referenced resource you can run it right in your browser right now via Jupyter environment served by As far as I can tell, it cannot fine-tune specifying how to break down that number further to say 2 substitutions and 1 deletion max.

ADD REPLYlink written 4 months ago by Wayne240

but it looks like PatMatch only works for Arabidopsis

ADD REPLYlink written 23 days ago by chahat_u50

@chahat_u PatMatch definitely isn't limited to Arabidopsis. Look at the other post I pointed at here. There are several web sites offering PatMatch working as a web tool for quite a few organisms beyond Arabidopsis. I list the ones I could find here. Additionally, as long as you have the sequence and go to and launch a binder session there, you can follow along with the example I set up and use another genome.

ADD REPLYlink written 9 days ago by Wayne240
gravatar for Maximilian Haeussler
3.6 years ago by
Maximilian Haeussler1.3k wrote:

Yes, bwa will find it, but you need to change the parameters. Do not use the seeded mode, use the slower -N mode:

bwa aln -n 4 -o 0 -k 4 -N

The sanger CRISPR site uses more or less these parameters.

ADD COMMENTlink written 3.6 years ago by Maximilian Haeussler1.3k

Hi, I tried your method to find the genomic location of a DNA sequence in the hg19 genome, and I ran the following command -

bwa aln -n 4 -o 0 -k 4 -N hg19.fasta testmotif.fq > out.sai

But the out.sai file seemed to only have illegible stuff in it -

SAI  ÄÑÄø ˇˇˇ

Do you have some idea as to what could be going wrong?

ADD REPLYlink written 22 days ago by chahat_u50
gravatar for Jeremy Leipzig
5.1 years ago by
Philadelphia, PA
Jeremy Leipzig17k wrote:

vmatch is an excellent general aligner

The Vmatch large scale sequence analysis software

ADD COMMENTlink modified 5.1 years ago by Istvan Albert ♦♦ 77k • written 5.1 years ago by Jeremy Leipzig17k
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