VNTRs and STRs are examples of which type of polymorphism?

• A. Single nucleotide polymorphisms.
• B. Tandem repeat polymorphisms.
• C. Copy number variations.
• D. Insertion-deletion polymorphisms.

Answer: (B)

VNTRs and STRs form sequence repeats that occur one after another in the genome, and the polymorphism comes from how many repeat units each person has. This is classic tandem repeat polymorphism: the variable feature is the number of contiguous repeats, not a single base change, a large chunk being gained or lost, or a simple insertion/deletion without the repeating pattern. SNPs are single-base changes, CNVs are large stretches with altered copy number, and indels are insertions or deletions of sequence without the repeating unit concept. STRs (short units) and VNTRs (longer units) are both different-length repeats, so they’re grouped as tandem repeat polymorphisms.