SAT Subject Biology Practice Question 251: Answer and Explanation

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Question: 251

1. The table shows the restriction enzyme recognition sites present on a circular piece of DNA 4.0 kilobases (1 kb = 1,000 bases) long.

Which pair of restriction enzymes, used together, would produce a band that travels the farthest on an electropheresis gel?

A. Nde I and Pst I
B. Nde I and Eco RI
C. Sac I and Bam HI
D. Eco RI and Hind III
E. Bam HI and Hind III

Correct Answer: D

Explanation:

Digesting the plasmid with Eco RI and Hind III produces DNA fragments of approximately 0.3, 1.8, 1.0, and 0.7 kb in length. The 0.3 kb fragment is the shortest resulting from any of the answer choices, and smaller DNA fragments travel farther in gel electrophoresis.

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