Final answer:
In a codon, the least important base is generally the third base due to the wobble effect, where changes at this position often result in the incorporation of the same amino acid into the protein. The answer is option B.
Step-by-step explanation:
The question addresses the importance of the positions within a codon, a group of three nitrogen bases in nucleic acids that make up a code "word" of the genetic code. While the first two bases in a codon are crucial for specifying an amino acid, the third base often varies without affecting the amino acid that is incorporated into the protein. This phenomenon is known as the "wobble" effect. Therefore, the least important base in a codon is generally considered to be the third base.
It's important to note that although the third base is often called the "wobble" base and may tolerate some variation, mutations at this position can sometimes still have effects, such as when they alter the efficiency of codon-anticodon pairing.