Other DNA

Protein-coding sequences (specifically, coding exons) comprise less than 1.5% of the human genome.^[3] Aside from genes and known regulatory sequences, the human genome contains vast regions of DNA the function of which, if any, remains unknown. These regions in fact comprise the vast majority, by some estimates 97%, of the human genome size. Much of this is composed of:

repeat elements

• Tandem repeats
  • Satellite DNA
  • Minisatellite
  • Microsatellite
• Interspersed repeats
  • SINEs
  • LINEs

transposons

• Retrotransposons
  • LTR
    • Ty1-copia
    • Ty3-gypsy
  • Non-LTR
    • SINEs
    • LINEs
• DNA Transposons

pseudogenes

However, there is also a large amount of sequence that does not fall under any known classification.

Much of this sequence may be an evolutionary artifact that serves no present-day purpose, and these regions are sometimes collectively referred to as "junk" DNA. There are, however, a variety of emerging indications that many sequences within are likely to function in ways that are not fully understood. Recent experiments using microarrays have revealed that a substantial fraction of non-genic DNA is in fact transcribed into RNA,^[7] which leads to the possibility that the resulting transcripts may have some unknown function. Also, the evolutionary conservation across the mammalian genomes of much more sequence than can be explained by protein-coding regions indicates that many, and perhaps most, functional elements in the genome remain unknown.^[8] The investigation of the vast quantity of sequence information in the human genome whose function remains unknown is currently a major avenue of scientific inquiry.^[9]

http://en.wikipedia.org/wiki/Human_genome