SAT Subject Biology Practice Question 268: Answer and Explanation

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Question: 268

18. Scientists sequenced a portion of the aspartate transaminase enzyme from different species. The amino acid sequences are shown in the table. Each letter stands for an amino acid. Differences from the human sequence are indicated by bold letters. Missing amino acids are indicated by a dash (–).

Which pair of organisms is most similar in terms of the amino acid sequence shown?

A. Pig and horse
B. Chicken and rat
C. Human and pig
D. Alfalfa and yeast
E. Bacteria and yeast

Correct Answer: C


Humans and pigs have identical amino acids at all positions except two. All other pairs of species shown differ at three or more positions.

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