Much of this DNA has no known biological function and is sometimes referred to as "junk DNA". However, many types of noncoding DNA sequences do have known biological functions, including the transcriptional and translational regulation of protein-coding sequences. Other noncoding sequences have likely, but as-yet undetermined, functions (this is inferred from high levels of homology and conservation seen in sequences that do not encode proteins but, nonetheless, appear to be under heavy selective pressure). While this indicates that noncoding DNA should not be indiscriminately referred to as junk DNA, the lack of sequence conservation in a majority of noncoding DNA with no known function indicates that much of it may indeed be without function.
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