NCBI BLAST is like google for bioinformatics. It helps in quickly comparing any nucleotide or protein sequence with various databases stored at NCBI.
# Often used databases 1. Human genome + transcriptome - relevant for blastn 2. Mouse genome + transcriptome - relevant for blastn 3. NR/NT - non-redundant set of nucleotides - relevant for blastn 4. Assembled genomes - relevant for blastn 5. NR - non-redundant set of proteins - relevant for blastp
# You can include or exclude a class of organisms.