How might a gene mutation be silent, with no observable affect on a cell or an organism?
A. Many proteins are superfluous to the function of a cell. A gene mutation in a gene that encodes an unnecessary protein would have no observable affect on the cell or the organism.
B. Codons are complementary to anti-codons in tRNA. A gene mutation that changes a codon to its anti-codon would have no observable effect on the cell or the organism.
C. Several codons are stop codons. A gene mutation that inserts a stop codon when only a few amino acids remain in the peptide sequence would have no observable effect on the cell or the organism.
D. Many amino acids are coded by multiple codons. A gene mutation that encodes the same amino acid would have no observable effect on the cell or the organism.

There is approximately 64 base combination of codons (3 bases sequences) that are possible from the four bases nucleotides that make up our DNA. Yet there are only approximately 20 types of amino acids in our bodies. This means that other than the 4 start and stop codons, there is a lot of redundancy in the coding of amino acids by codons. Therefore some mutations on codons will have no effect on the type of amino acid translated. These are the silent mutations.