úrgangsefna

Urgangsefna, the Icelandic term commonly translated as junk DNA, refers to portions of an organism’s genome that do not code for proteins. The concept encompasses noncoding DNA, including introns within genes, regulatory sequences such as promoters and enhancers, repetitive elements, transposable elements, and pseudogenes. Historically, these regions were viewed as evolutionary leftovers with little function, hence the label junk.

Many regions once dismissed as junk have recognized roles. Some noncoding DNA contains regulatory elements that influence when and where genes are turned on or off. Noncoding RNAs produced from these regions, including microRNAs and long noncoding RNAs, participate in gene expression and RNA processing. Repetitive elements and transposons can shape genome structure and evolution, and in some cases contribute to new genes or regulatory networks.

Genome projects and comparative genomics show that the size and composition of noncoding DNA vary widely across species. While a large fraction of noncoding sequences remains functionally enigmatic, accumulating evidence indicates that a substantial portion is under selective constraint and contributes to genome organization and stability. The label junk DNA is used less in contemporary debate, with emphasis on noncoding DNA and its diverse roles.