New genes out of nothing

One key question in evolutionary biology is how novel genes arise and develop. Swedish researchers now show how new genes and functions that are advantageous to bacteria can be selected from random DNA sequences. The results ...

Oldest Scandinavian human DNA found in ancient chewing gum

The first humans who settled in Scandinavia more than 10,000 years ago left their DNA behind in ancient chewing gum, masticated lumps made from birch bark pitch. This is shown in a new study conducted at Stockholm University ...

Tiny light-up barcodes identify molecules by their twinkling

An imaging technique developed at Duke University could make it possible to peer inside cells and watch dozens of different molecules in action at once—by labeling them with short strands of light-up DNA that blink on and ...

Study: Some woodpeckers imitate a neighbor's plumage

In the first global test of the idea, scientists have found evidence that some woodpeckers can evolve to look like another species of woodpecker in the same neighborhood. The researchers say that this "plumage mimicry" isn't ...

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DNA sequence

A DNA sequence or genetic sequence is a succession of letters representing the primary structure of a real or hypothetical DNA molecule or strand, with the capacity to carry information as described by the central dogma of molecular biology.

The possible letters are A, C, G, and T, representing the four nucleotide bases of a DNA strand — adenine, cytosine, guanine, thymine — covalently linked to a phosphodiester backbone. In the typical case, the sequences are printed abutting one another without gaps, as in the sequence AAAGTCTGAC, read left to right in the 5' to 3' direction. Short sequences of nucleotides are referred to as oligonucleotides and are used in a range of laboratory applications in molecular biology. With regard to biological function, a DNA sequence may be considered sense or antisense, and either coding or noncoding. DNA sequences can also contain "junk DNA."

Sequences can be derived from the biological raw material through a process called DNA sequencing.

In some special cases, letters besides A, T, C, and G are present in a sequence. These letters represent ambiguity. Of all the molecules sampled, there is more than one kind of nucleotide at that position. The rules of the International Union of Pure and Applied Chemistry (IUPAC) are as follows:

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