Base Pair (Bp)
Definition
A complementary pairing of nitrogenous bases on opposite strands of double-stranded DNA: adenine with thymine (two hydrogen bonds) or guanine with cytosine (three hydrogen bonds). Fragment length in forensic analysis is measured in base pairs, and the number of repeating base pairs defines STR allele sizes.
- Unit of
- Double-stranded DNA length
- A-T bond
- 2 hydrogen bonds
- G-C bond
- 3 hydrogen bonds
- Forensic use
- Measures STR allele and fragment size
Common questions
Why is bp the standard unit in STR reports rather than a molecular weight?+
STR alleles differ from each other by whole repeat units, and repeat units are naturally counted in base pairs, so reporting fragment size in bp lets an examiner directly infer the number of repeats and therefore the allele call from capillary electrophoresis output.
What can cause a base pair size to be misread during analysis?+
Stutter artefacts from polymerase slippage, or non-template adenylation adding an extra base to some fragments, both shift the apparent size by roughly one bp and can be mistaken for a true allele if not accounted for in the analysis software's bin allocation.
Related terms
- Antiparallel Orientation
- The two strands of the DNA double helix run in opposite directions: one strand reads 5' to 3', its complement reads 3'...
- Complementarity
- The property by which each base pairs with only one specific partner (A with T, G with C). Complementarity allows a single...
- Denaturation
- The separation of double-stranded DNA into two single strands by disrupting the hydrogen bonds between base pairs. In PCR, denaturation is achieved...
- Nucleotide
- The monomer unit of nucleic acids. Each nucleotide consists of a five-carbon sugar (deoxyribose in DNA, ribose in RNA), a phosphate group,...
- Phosphodiester Bond
- The covalent linkage between consecutive nucleotides in a strand, formed between the phosphate group and the 3'-OH of the preceding sugar and...