Various types of primers and probes are available from several suppliers for applications in molecular biology. Used in PCR-based amplification, oligonucleotide primers guide the activity of polymerases in order to amplify gene-specific sequences. Non-specific primers, such as random hexamers and oligo-dT primers, are used in the synthesis of cDNA and DNA hybridization probes. DNA and RNA probes are labeled oligonucleotides used in hybridization experiments, such as nucleic acid blotting, in situ hybridization and FISH.
Random primers are mixtures of oligonucleotides (usually hexamers or nonamers) that contain random nucleotides sequences. The mixture contains all possible combinations of nucleotides that can be used in initiating DNA synthesis for single-stranded DNA as well as RNA templates regardless of the presence of polyA tails. In addition to cDNA synthesis, random primers can be used to prepare DNA probes for hybridization.