BLAST is a sequence similarity search program that compares biological sequences like protein or DNA sequences to sequence databases. It was developed by researchers at the National Institutes of Health and published in 1990. BLAST uses substitution matrices to find short matches between sequences and detect both local and global alignments. There are different BLAST programs that compare nucleotide or protein queries against nucleotide or protein databases. BLAST is useful for identifying species, establishing phylogeny, DNA mapping, and locating domains in protein sequences.

1. BLAST
Kishan Sharma
M.Sc. 2nd Year
Biotechnology
Manipal University
Jaipur

2. BLAST
 Basic Local Alignment Search Tool
 It is a sequence similarity search program for comparing
biological sequences such as amino acid sequence of
different proteins or the nucleotides of DNA sequences with
sequence database or library sequences.

3. BLAST
 BLAST was designed by Eugene Myers , Samuel Karlin ,
Stephen Altschul, Warren Gish, David J. Lipman and Webb
Miller at the National Institute of Health and was published in
Journal of Molecular Biology in 1990.
 It was originally developed & controlled by NCBI .
 Link: http://www.ncbi.nlm.nih.gov/BLAST/

4. BLAST
 Sequence alignments provide a powerful way to compare
sequences with previously characterized genes.
 Both functional and evolutionary information can be inferred from
well designed queries and alignments.
 The BLAST detects local as well as global alignments and regions
of similarity in unrelated proteins can be detected.

5. BLAST

6. BLAST types
 Blastp : compares protein query against proteins sequence
database.
 tBlastn : Compares a protein query sequence against a
nucleotide sequence database.
 Blastn : compares nucleotide query against nucleotide
sequence database.

7. BLAST types
 Blastx : Compares a nucleotide query sequence translated in
all reading frames against a protein sequence database.
 This option may be used to find potential translation
products of an unknown nucleotide sequence.
 tBlastx : compares nucleotide query against translated
nucleotide sequence database.

8. BLAST
 All BLAST programs use a substitution scoring matrix (BLOSUM or
PAM), determines pair-wise alignment scores.
 BLAST finds homologous sequences , not by comparing either
sequences in its entirety, but rather by locating short matches
between the two sequences.

9. NCBI Home page

10. NCBI-BLAST Home Page

11. Applications of BLAST
 Identifying Species: With the use of BLAST, you can possibly correctly
identify a species and/or find homologous species.
 This can be useful, for example, when one is working with a DNA
sequence from an unknown species.
 Establishing Phylogeny: Using the results received through BLAST,
one can create a phylogenetic tree using the BLAST web-page.

12. Applications of BLAST
 DNA Mapping: When working with a known species, and looking to
sequence a gene at an unknown location, BLAST can compare the
chromosomal position of the sequence of interest, to relevant sequences
in the database.
 Locating Domains: When working with a protein sequence you can
input it into BLAST, to locate known domains within the sequence of
interest.
 Comparison: When working with genes, BLAST can locate common
genes in two related species, and can be used to map annotations from
one organism to another.

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