Genetics Review
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Base Pair back to top

Source:  image from the National Human Genome Research Institute (NHGRI) Genetic Illustrations.

Definition back to top

A base pair refers to two bases which form a "rung of the DNA ladder." A DNA nucleotide is made of a molecule of sugar, a molecule of phosphoric acid, and a molecule called a base. The bases are the "letters" that spell out the genetic code. In DNA, the code letters are A, T, G, and C, which stand for the chemicals adenine, thymine, guanine, and cytosine, respectively. In base pairing, adenine always pairs with thymine, and guanine always pairs with cytosine.

Source:  definition from the National Human Genome Research Institute (NHGRI) Glossary of Genetic Terms.
More... back to top

Nucleotide Base Codes

In addition to the letters A, C, T, and G, a number of other abbreviations can be used to represent the nucleotide bases. Those abbreviations are provided by the IUPAC (International Union of Pure and Applied Chemistry) and are available in "Appendix V: Controlled Vocabularies" of the DDBJ/EMBL/GenBank Feature Table.

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  Revised September 29, 1999
Comments/questions to Renata Geer