Final answer:
The GAU codon mutation to GAG represents a silent mutation, where the amino acid aspartic acid remains unchanged, likely resulting in a minimally altered protein function. option a is correct.
Step-by-step explanation:
The mutation of the codon GAU to a codon that would result in a protein with unaltered or minimally altered function is most likely GAG. This is because GAU codes for the amino acid aspartic acid (Asp), and GAG also codes for aspartic acid due to the redundancy of the genetic code. This type of mutation is known as synonymous or silent mutation, where the change in the nucleotide sequence does not result in a change in the amino acid sequence of the protein.
Mutations in the third base of a codon often have less drastic effects, sometimes still coding for the same amino acid due to the 'wobble' base phenomenon. However, when it comes to altering protein function, some mutations, like nonsense mutations or insertion mutations that change the reading frame, can have more severe consequences.
Nonsense mutations create a stop codon, leading to an incomplete protein that's often nonfunctional. Insertion mutations can cause a frame shift leading to completely different amino acids being incorporated downstream of the mutation or causing premature truncation of the protein.