DNA fingerprinting works because individuals (except identical twins) differ in the lengths and sequences of highly polymorphic regions of their DNA, which can be compared across samples. Which type of DNA variation is most commonly exploited in classic DNA fingerprinting?

• A. Differences in the universal genetic code that assign different amino acids to the same codons in different people
• B. Variable number tandem repeats (VNTRs) or short tandem repeats (STRs) that vary in repeat number among individuals
• C. Large differences in the number of chromosomes between unrelated individuals within a species
• D. Widespread variation in mitochondrial DNA inheritance such that mtDNA is inherited equally from both parents in most people

Answer: (B)