Question

Which of the following is not a variant of BLAST?

• A. BLASTX
• B. TBLASTNX
• C. BLASTP
• D. BLASTN

Hint:

• Common BLAST programs:
  • blastn Nucleotide query vs. nucleotide database.
  • blastp Protein query vs. protein database.
  • blastx Translated nucleotide query vs. protein database.
  • tblastn Protein query vs. translated nucleotide database.
  • tblastx Translated nucleotide query vs. translated nucleotide database.

Answer 1

The Correct Option is B

BLAST (Basic Local Alignment Search Tool) is a suite of programs used to compare biological sequence information (DNA or protein sequences) against sequence databases to find regions of local similarity. Different BLAST programs are designed for different types of query and database sequences:

• BLASTN (Option d): Compares a nucleotide query sequence against a nucleotide sequence database.
• BLASTP (Option c): Compares an amino acid (protein) query sequence against a protein sequence database.
• BLASTX (Option a): Translates a nucleotide query sequence in all six possible reading frames and compares these translated protein sequences against a protein sequence database. (Nucleotide query vs. Protein database).
• TBLASTN: Translates a protein query sequence against a nucleotide sequence database (where database sequences are translated in all six reading frames). (Protein query vs. Nucleotide database).
• TBLASTX: Translates both the nucleotide query sequence and the nucleotide database sequences in all six reading frames, and then compares the resulting protein sequences. (Translated Nucleotide query vs. Translated Nucleotide database).

Let's analyze the options: (a) BLASTX: A standard BLAST variant (Nucleotide query translated \(\rightarrow\) Protein DB). (b) TBLASTNX: This is an unusual concatenation. Standard variants are TBLASTN and TBLASTX. If "TBLASTNX" is meant to be "TBLASTX", it is a valid variant. If it's a typo for "TBLASTN", that's also valid. However, "TBLASTNX" as a single program name is not standard. (c) BLASTP: A standard BLAST variant (Protein query \(\rightarrow\) Protein DB). (d) BLASTN: A standard BLAST variant (Nucleotide query \(\rightarrow\) Nucleotide DB). The question asks which is "not a variant". TBLASTNX is not a standard name for a BLAST program. The components TBLASTN and TBLASTX are standard. It's likely that TBLASTNX as written is the intended "not a variant". If the options are to be taken literally, TBLASTNX is not a recognized BLAST program name. \[ \boxed{\text{TBLASTNX}} \]