Question

Examine the data showing the percent identity of the GAPDH gene and protein sequences between humans and the three species shown below.

Species	Gene Identity	Protein Identity
Chimpanzee	99.6%	100%
Fruit Fly	72.4%	76.7%
Roundworm	68.2%	74.3%

Provide a possible reason for why the percent identity between gene sequences is lower than the percent identity of protein sequences.

• A. Multiple codons code for the same amino acid.
• B. Introns are likely to have different sequences.
• C. Differences in DNA sequences are edited when the mRNA is transcribed.
• D. Amino acids cannot be substituted without consequence.

Answer 1

The correct option is A Multiple codons code for the same amino acid.

It is seen from the table that percent identity between gene sequences is lower than the percent identity of protein sequences. This is because multiple codons code for the same amino acid. Hence, the single protein can be made by different base sequences. This results in production of identical amino acids from different codons or sequences.

Thus, the correct answer is 'Multiple codons code for the same amino acid.'