tetranucleotide

A tetranucleotide is a sequence of four nucleotides, the basic building blocks of nucleic acids. In DNA, the four bases are adenine (A), cytosine (C), guanine (G), and thymine (T); in RNA, thymine is replaced by uracil (U). The term can refer to any contiguous four-nucleotide sequence, such as ATCG or GACA, and to longer constructs that are built from repeats of a four-nucleotide unit.

A tetranucleotide repeat, or tetra-nucleotide VNTR, is a tandemly repeated four-nucleotide motif. Individuals differ in the number of repeats at many loci, providing genetic polymorphism that is useful for analysis. Tetranucleotide repeats are a subset of short tandem repeats (STRs). They are favored in some forensic and paternity tests because they often yield clearer allele calls with less stutter than shorter dinucleotide repeats, enabling high-resolution, automated genotyping. Common tetra-nucleotide motifs used in typing panels include units such as GATA, AATG, or ACTG, though the specific unit depends on the locus.

Beyond human forensic use, tetranucleotide repeats are also studied in microbial typing (for example, multilocus VNTR analysis, MLVA) and population genetics to characterize genetic diversity. They provide a practical means to compare genetic similarity and trace lineage relationships across samples.

Historically, the term tetranucleotide relates to early notions about DNA composition, but modern genetics recognizes DNA as a polymer of four nucleotides whose function derives from sequence, not a fixed four-unit repeating pattern.