Non-coding DNA (or "junk DNA") refers to a DNA sequence that does not contain instructions to make protein, or can only make RNA without translation ability. This DNA is the majority in the genome of eukaryotes. For a long time, scientists did not think of these non-coding effects, so these repeated DNA fragments were labeled as junk DNA. With the passage of time, scientists have gradually deepened their understanding of junk DNA, and gradually found that many non-coding DNA has its unique functions, and they play an important role in gene shearing.

The number of non-coding regions is closely related to the degree of biological evolution. In microorganisms, the non-coding region only accounts for 10%-20% of the whole genome sequence. However, in higher organisms and human genomes, non-coding sequences account for the vast majority of genome sequences.

For a long time, one of the main research directions of non-coding region is the research of regulatory elements. Because in the non-coding region, only a small part is proved to be a useful component, which can help genes turn on and off to regulate gene expression, that is, the famous regulatory DNA. Most non-coding DNA is still controversial, because their functions have not been recognized, so people don't know whether they should be regarded as garbage.