Practice question

Due to degeneracy of genetic code, many third-position base changes leave amino acid unchanged because multiple codons encode same residue. Such synonymous substitutions maintain protein primary structure, so enzymatic activity and fold remain comparable, earning term neutral or silent mutation as selection pressure minimal. However synonymous sites are not universally neutral, as codon usage bias affects translation rate, mRNA folding, and exonic splicing enhancers, meaning phenotypic neutrality depends on context though amino acid sequence preservation remains true. This principle illustrates essential molecular mechanisms governing replication fidelity and mutation fixation relevant for exam interpretation.