1. Primer extension * This labelling technique uses random oligonucleotides (usually hexadeoxyribonucleotide molecules- sequences of six deoxynucleotides) to primer synthesis of a DNA strand by DNA polymerase. * The DNA to be labelled is denaturated by heating, and the oligonucleotide primer annealed to the single stranded DNAs.

2. The klenow fragment of DNA polymerase can synthesize a copy of the template, primed from the 3-hydroxyl group of the oligonucleotide. * If a labelled dNTP is incorported, DNA of very high specific activity is produced. (Fig 12)The klenow fragment of DNA polymerase can synthesize a copy of the template, primed from the 3-hydroxyl group of the oligonucleotide. * If a labelled dNTP is incorported, DNA of very high specific activity is produced. (Fig 12)

4. Nucleic acid hybridization The complementary feature of DNA base-pairing can be used to provide information a bout the sequence complexity of the DNA.The complementary feature of DNA base-pairing can be used to provide information a bout the sequence complexity of the DNA. If a DNA duplex is denaturated by heating until the strands separate, the complementary strands will be renaturated on cooling. (Fig 13)If a DNA duplex is denaturated by heating until the strands separate, the complementary strands will be renaturated on cooling. (Fig 13)