Almost all organisms translate their genes into protein structures using an identical, universal codon dictionary in which each amino acid in the protein is represented by a combination of only three nucleotides. For example, the sequence AAA in a gene is transcribed into the sequence UUU in messenger RNA (mRNA) and is then translated as the amino acid phenylalanine. A group of several codons that, taken together, provide the code for an amino acid, is called a reading frame. There are no "spaces" in the mRNA to denote the end of one codon and the start of another. Instead, the reading frame, or group of triplets, is determined solely by initial position of the pattern-making machinery at the start of the translation. In order for correct translation to occur, this reading frame must be maintained throughout the transcription and translation process.

Any single or double base...