BLAST stands for Basic Local Alignment Search Tool (Altschul et al 1990). It allows you to query a sequence database with a sequence in order to find entries in the database that contain similar sequences. When “BLAST-ing”, you are able to specify either nucleotide or protein sequences and nucleotide sequences can be either DNA or RNA sequences. Sequences can be BLAST-ed against databases held at NCBI (see NCBI BLAST), or contained within your local Geneious database (Custom BLAST).