Which of the following describes a triplet in DNA?

A triplet in DNA refers to a sequence of three nucleotide bases, and this sequence plays a crucial role in the genetic code. Each triplet, also known as a codon, corresponds to a specific amino acid during the process of protein synthesis. Therefore, the correct choice is that it codes for a single amino acid. This means that when the information contained in DNA is transcribed to RNA and then translated into proteins, the triplet sequences are read in sets of three, with each set specifying which amino acid should be added to the growing polypeptide chain.

Understanding the function of triplets is fundamental in molecular biology, as they directly link the genetic code stored in DNA to the physical characteristics and functions of living organisms. While the other options suggest either incorrect definitions of a triplet's structure or role in DNA, the designation of coding for a single amino acid highlights the triplet’s importance in translating genetic information into functional proteins.