blastn with short sequences gives no results in the corresponding genome
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Entering edit mode
20 months ago
A_heath ▴ 100

Hi all,

I've designed primers to identify a strain of interest.

Just to be sure that the primers matche only the genome of this strain and no other genomes, I am using blastn analysis.

My input file is :

>Seq_1
ATGTGCTAGCTATGGCG
>Seq_2
GTCGGTAATCGATTCGA


And my database is a multifasta file containing several genomes including the genome of my strain of interest.

My command line is the following :

> blastn -query Sequences.fasta -db genomes.fasta -out Results_blastn.txt -outfmt 6 -evalue 0.1


The results file is blank.

I do not understand how I've got no results even on the genome of my strain of interest ...

Do someone have an idea on how I should proceed to fix this issue?

Thank you so much in advance for your much appreciated help!

Audrey

blastn output primers • 510 views
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Entering edit mode

You might want to take a look specifically at PrimerBlast (https://www.ncbi.nlm.nih.gov/tools/primer-blast/) which is designed specifically for this.

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Entering edit mode
20 months ago

Just add -task blastn-short to your command. By default, blastn uses megablast (optimized for highly similar long sequences).

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Entering edit mode

Indeed, it works better now ... Thank you so much for your help a.zielezinski!