BLAST Tutorial

Learn how to perform sequence similarity searches using BLAST

Introduction

BLAST (Basic Local Alignment Search Tool) is one of the most widely used bioinformatics tools for sequence similarity searching. This tutorial will guide you through the process of using BLAST to find similar sequences in databases.

Prerequisites: Basic understanding of molecular biology and sequence analysis concepts.

Step 1: Accessing BLAST

To start using BLAST, visit the NCBI BLAST website at https://blast.ncbi.nlm.nih.gov.

Key Points:

  • Choose the appropriate BLAST program for your sequence type
  • Prepare your query sequence in FASTA format
  • Select the appropriate database for your search

Step 2: Preparing Your Query

Your query sequence should be in FASTA format. Here's an example:

>Query_sequence
ATGCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCGATCG

Make sure your sequence is properly formatted and free of any special characters or spaces.

Step 3: Configuring BLAST Parameters

BLAST offers several parameters that you can adjust to optimize your search:

Basic Parameters

  • E-value threshold
  • Word size
  • Scoring matrix

Advanced Parameters

  • Gap costs
  • Filtering options
  • Output format

Step 4: Interpreting Results

BLAST results include several important components:

Graphical Overview

Visual representation of sequence alignments

Descriptions

List of significant matches with scores and E-values

Alignments

Detailed pairwise alignments of query and subject sequences

Additional Resources

Video Tutorials

Step-by-step video guides for using BLAST

Watch tutorials →

Practice Exercises

Hands-on exercises to improve your BLAST skills

Start exercises →

Related Tutorials

Other tutorials that might interest you

Related Software

  • ClustalW

    Multiple sequence alignment

  • MUSCLE

    Multiple sequence alignment

  • MAFFT

    Multiple sequence alignment