 Dear students, in this module, I'll be introducing you to BLAST. BLAST is the most commonly used software by bioinformations all around the world. BLAST is essentially a tool to compare biological sequences. As you would already know, you can perform local and global alignments using algorithms such as Needleman Munch and Smith Waterman. However, in real life, you need to do this very fast and several times. So it is a bit difficult to do Smith Waterman or Needleman Munch every time. So here is this tool, BLAST, that is available online free of any cost and it was developed and made available by National Center for Biotechnology Information or simply NCBI in 1990. The acronym BLAST comes from the basic local alignment search tool. So towards the background, you need to be able to search biological sequences in a brisk manner. For instance, if you have hundreds of sequences that you want to compare quickly, then you cannot go about running Smith Waterman or Needleman Munch using a pen and paper and doing it over a hundred times. So here is this tool that can help you do all of that in a very short amount of time. More so, it can help you to look at the translational products that come from the genes that is the nucleotide sequences. The online link for this tool is provided here and you can follow this link and look at the user interface for BLAST. If you go to this link, this is how it will look like. So here is the software's name BLAST and you can BLAST or compare sequences from multiple organisms that are listed here. At this point, I would like to indicate to you that when I say BLAST the sequences, it essentially means compare the sequences or align the sequences. So BLASTing is a commonly used term by the bioinformaticians which essentially means comparing the sequences. So if you scroll down this page, you will find that there are several types of BLAST such as nucleotide BLAST that is mentioned here or after nucleotide BLAST, protein BLAST, BLASTX, TBLASTN, TBLASTX. So you need to be in a position to select which kind of BLAST algorithm you want to use. So each one of them has a specific purpose. So let's take a look. For the nucleotide BLAST, you simply search for nucleotides. So you have a query nucleotide. So query is the sequence that you are trying to search within the database. So here is your database DB simply. So you search for query sequence in the database. So in case of nucleotide BLAST, your query sequence is a nucleotide. Sequence and your DB is a nucleotide DB. For protein BLAST, your query is a protein sequence and your database is a protein database. Moreover, there are other types of BLAST such as BLASTX which have a protein database as I just mentioned and the query is a nucleotide sequence. So you are searching for a nucleotide sequence in a protein database. That sounds weird. So we translate this nucleotide sequence into the protein sequence first and then search it in the protein DB. You also have TBLASTN in which you have a translated nucleotide database and your query sequence is a protein. And you have TBLASTX which means you have a translated nucleotide database just like the previous case but your query is a translated nucleotide sequence. So given these multiple types of BLAST, you can easily search for nucleotide or amino acid sequences in the available sequence databases. To start with, if you click on BLASTN, this is the nucleotide BLAST, then you will arrive at this user interface. Here you can list the FASTA sequence, the IDs or the accession numbers of the nucleotide sequences you want to search and it will search in the database that you want to search in. You also have the protein BLAST or BLASTP by clicking here on this tab and you can input your protein IDs here and specify the protein database and go for the search. So in conclusion, BLAST is a software tool that you can employ to compare nucleotide or protein sequences with databases that have nucleotide or amino acid sequences. BLAST helps you to perform this task in a short amount of time and therefore is a commonly used tool by the bioinformaticians. More so, it is available online and free of cost.