DNA在转录RNA时，只有一条链会转录成RNA，与RNA串行直接拷贝的脱氧核苷酸串行（以U代替T）的DNA链则为有义链（编码链）。另一条链作RNA合成过程中核糖核苷酸碱基配对的模板，称为反义链（模板链）。

In genetics, a sense strand, or coding strand, is the segment within double-stranded DNA that runs from 5' to 3', and which is complementary to the antisense strand of DNA, which runs from 3' to 5'. The sense strand is the strand of DNA that has the same sequence as the mRNA, which takes the antisense strand as its template during transcription, and eventually undergoes (typically, not always) translation into a protein. The antisense strand is thus responsible for the RNA that is later translated to protein, while the sense strand possesses a nearly identical makeup to that of the mRNA. Note that for each segment of dsDNA, there will possibly be two sets of sense and antisense, depending on which direction one reads (since sense and antisense is relative to perspective). It is ultimately the gene product, or mRNA, that dictates which strand of one segment of dsDNA we call sense or antisense. But keep in mind that sometimes, such as in prokaryotes, overlapping genes on opposite strands means the sense for one mRNA can be the antisense for another mRNA.