In DNA profiling, what determines the length of fragments produced by restriction enzymes?

• A. The enzyme used in the digestion
• B. The overall size of the genome
• C. The specific base sequences recognized by restriction enzymes
• D. The duration of the digestion

Answer: (C)

Restriction enzymes cut DNA at specific sequences, so the lengths of the fragments are determined by where those recognition sites occur along the DNA. The enzyme only cuts where its particular base sequence is found, so the distances between successive cut sites set the fragment sizes. Choosing a different enzyme changes which sites are cut and thus the pattern of fragment lengths, but it remains the arrangement of those recognition sequences in the genome that fixes the lengths. The overall genome size isn’t a direct determinant of fragment length, and digestion time mainly affects whether sites are fully cut rather than where they are cut.