Which statement about VNTRs and STRs is true?

• A. VNTRs and STRs vary in number between individuals.
• B. VNTRs and STRs do not vary between individuals.
• C. VNTRs and STRs occur only in plants.
• D. VNTRs and STRs are not repeating sequences.

Answer: (A)

VNTRs and STRs are regions of DNA where a short sequence is repeated in tandem, and the number of repeats at a given location can differ from person to person. This copy-number variation across many loci makes these regions highly polymorphic, which is why they’re so useful for identity testing and forensic genetics. The statement that they vary in number between individuals is the true one because, unlike non-repeating sequences, their repeat counts differ among people. They are not restricted to plants, and they are indeed repeating sequences by definition. For completeness, VNTRs have longer repeat units than STRs, but both show variation in copy number.