Transposable elements are intriguing components of non-coding DNA that exhibit behavior similar to viruses by inserting their DNA into various locations within the genome. These elements are categorized into two main types: transposons and retrotransposons. Transposons utilize a DNA intermediate for insertion, while retrotransposons employ an RNA intermediate. A notable subtype of retrotransposons is the long interspersed nuclear element (LINE), which is unique because it encodes for the enzyme reverse transcriptase. This enzyme facilitates the conversion of RNA back into DNA, allowing the LINE to integrate its sequence into the genome effectively.

In the structure of a LINE, there are genes responsible for transposition, which enable the movement of the element, flanked by long terminal repeats that are often considered non-functional or "junk" DNA. Another form of non-coding DNA is pseudogenes, which are remnants of once-functional genes that have lost their activity due to mutations. Although they were once capable of coding for proteins, they are now inactive and contribute to the vast array of non-coding DNA in the genome.

MicroRNA (miRNA) is another important type of non-coding DNA that, while not coding for proteins, plays a crucial role in gene regulation through RNA interference mechanisms in eukaryotes. Additionally, non-coding DNA is found within genes in the form of introns, which are segments that do not code for proteins but are interspersed within protein-coding sequences.

For instance, a comparison between a chimpanzee gene and its human counterpart illustrates how insertions and deletions can render a gene non-functional, transforming it into a pseudogene. Overall, the eukaryotic genome is predominantly composed of non-coding DNA, with only a small fraction dedicated to protein-coding sequences, highlighting the complexity and significance of these non-coding elements in genetic regulation and evolution.