Tandem repeat polymorphisms can contribute to phenotypic variation.

• A. They have no impact on phenotype.
• B. They are always detrimental to health.
• C. They can contribute to phenotypic variation among individuals.
• D. They occur only in exons.

Answer: (C)

Tandem repeat polymorphisms are different numbers of short DNA motifs repeated in a row at the same genomic location. Because the repeat count can vary between individuals, these loci mutate more often than many other sites, creating substantial allelic diversity. That variability can influence phenotype in multiple ways: changes in repeat length within coding regions can alter protein length or function; repeats in regulatory regions can affect how strongly a gene is expressed; repeats in noncoding regions can influence RNA processing, stability, or localization. All of this means that the number of repeats can contribute to differences in traits or disease susceptibility among people. They aren’t always harmful, and they aren’t limited to exons; they can occur in many genomic contexts. That’s why the statement that tandem repeat polymorphisms can contribute to phenotypic variation is correct.