Afascinating property of DNA is the complementarity of the nucleotide bases in its two anti-parallel strands, with G always pairing with C and A always pairing with T. This does not involve strong covalent chemical bonds but weak hydrogen bonds. There are three hydrogen bonds between G-C pairs and two between A-T pairs, so strand separation is easier in AT-rich DNA than in GC-rich DNA. Mild heating breaks these hydrogen bonds and is one way to separate the two strands, called denaturation or dissociation. Reducing the temperature under the right salt conditions leads to renaturation (reassociation or reannealing) of the two strands by reconstitution of the hydrogen bonds. The rate of renaturation depends on the frequency of collision between complementary sequences, which depends on their concentration. The concentration and time required for renaturation determines the Cot value (concentration × time). If a high concentration of labeled probe DNA is used, hybridization to complementary nucleic acid sequences in the target preparation can be achieved in a reasonably short time. These properties of DNA are extremely important, because they make it possible to detect specific DNA sequences (such as genes) on a nitrocellulose filter (molecular hybridization) or in cytological preparations (in situ hybridization) by using labeled DNA or RNA probes.
KeywordsSorting DAPI Tral Photolysis Tritium
Unable to display preview. Download preview PDF.
- Chen Z, Grebe TA, Guan X-Y, et al. (1997) Maternal balanced translocation leading to partial duplication of 4q and partial deletion of 1p in a son: cytogenetic and FISH studies using band-specific painting probes generated by chromosome microdissection. Am J Med Genet 71: 160–166PubMedCrossRefGoogle Scholar
- DeCapoa A, Felli MP, Baldini A, et al. (1988) Relationship between the numbers and function of human ribosomal genes. Hum Genet 79:301–304Google Scholar
- Harper ME, Saunders GF (1984) Localization of single-copy genes on human chromosomes by in situ hybridization of 3H-probes and autoradiography. In: Sparkes RS, de la Cruz FF (eds) Research perspectives in cytogenetics. University Park Press, Baltimore, pp 117–133Google Scholar