The expansion of repetitive elements (such as Alu sequences) has even infiltrated the transcriptional units of the mammalian genome. This results in transcription units that are frequently much larger (30–200 kb), commonly containing multiple promoters and DNA repeats within untranslated introns.
Repetitive elements, like Alu sequences, have even invaded the transcriptional domains of the mammalian genome. As a result, transcription units often grow to be 30–200 kb in size, frequently encompassing multiple promoters and DNA repeats embedded within non-coding introns.