Expressed Sequence Tag is defined as (A) a partial sequence of a codon randomly selected from cDNA library (B) the characteristic gene expressed in the cell (C) the protein coding DNA sequence of a gene (D) uncharacterized fragment of DNA present in the cell

Answer: (A) a partial sequence of a codon randomly selected from cDNA library
An Expressed Sequence Tag (EST) is a short, unique sequence of a cDNA clone that represents a part of the expressed gene. It is used to identify and catalog gene transcripts. The other options do not accurately describe ESTs.