Tetranucleotides

Tetranucleotides are sequences consisting of four nucleotides found in DNA or RNA. In genetics, the term is frequently used to describe tetranucleotide short tandem repeats (STRs), a class of microsatellite markers in which a four-base motif is repeated in tandem. These four-base motifs can occur throughout the genome and provide a source of length polymorphism useful in genetic analysis and fingerprinting.

There are 4^4 = 256 possible four-base motifs. Because DNA is double-stranded and many analyses group motifs with their reverse complements, the number of unique tetranucleotide motif families is smaller, commonly cited as 136 when reverse complements are treated as the same. Tetranucleotide repeats arise through DNA polymerase slippage during replication and vary in repeat number among individuals. They typically produce cleaner PCR profiles than shorter repeats, making them attractive as genetic markers.

Applications of tetranucleotide STRs include forensic identification, paternity testing, and population genetics. In genomics and bioinformatics, tetranucleotide usage patterns have been used to study genome composition, detect contamination, and aid in binning metagenomic sequences. Overall, tetranucleotides are a basic unit of sequence analysis with both structural and analytical importance in modern genetics.