BLAST

(Altschul et al. 1990 & 1997)

Basic Local Alignment Search Tool (BLAST)

BLAST is a software tool for searching similarity in nucleotide sequences (DNA) and/or amino acid (protein) sequences.

• • similarity search of nucleotide or amino acid sequences

  • allows gaps (deletions and insertions)

  • local alignment: detect regions (subsequences) that are similar between two compared sequences

  • homology search of gene or protein sequences. For short read mapping see bowtie2 or BWA.

BLAST homepage

https://blast.ncbi.nlm.nih.gov/

Blast online webtools

https://blast.ncbi.nlm.nih.gov/BlastSearch → help.pdf → guide

https://www.ebi.ac.uk/Tools/sss/ncbiblast/nucleotide.html

http://www.genome.jp/tools/blast/

https://genome.jgi.doe.gov/

→ Install Blast locally

Blast FAQ

https://blast.ncbi.nlm.nih.gov/blast/FAQ

Options

→ E-Value & Bit-score

→ Word-size

Blast results

blastn -query genes.fasta -subject genome.fasta -outfmt 6

→ BLASTn output format 6

Blast database

makeblastdb -in ecoli.fasta -parse_seqids -dbtype nucl

→ Create BLAST database

Alternative tools

→ Bowtie2 to map short reads (shotgun sequencing) against reference genomes

→ FastANI to compare (draft) genomes by Average Nucleotide Identity (ANI)

read more

Altschul et al. 1990

Altschul et al. 1997