gotta agree with burnt, junk dna is a very old and totally outdated term. It was coined at around the time of the release of the first draft of the human genome yet since then people have found much more info on "junk" DNA and what it does.
Just for the record, all organisms have junk DNA. It seems that more complex organisms have more of it, with bacteria having the least amount and higher plants and animals having the most.
This non-coding DNA does the following:
1. Contains regulatory sequences that control the expression of genes. In this way different cell types in an organism are different (e.g. epidermal cells are different from neurons etc.)
2. Other sequences are useful for attracting a special environment to make euchromatin/heterochromatin. Many of them are the remains of viruses that popped into the genome, got mutated and stayed there. (HIV is a type of virus that likes to pop its dna in and out of the human genome)
3. Other sequences are used to make the centromeres, the structures that hold chromosomal strands together during mitosis whereas others make the telomeres, the structures that protect the end of chromosomes and ensure their replication.
4. Others are the remains of no more active genes that serve as a "spares part list" for the potential creation of new genes. Something like the inventory of a workshop.
5....whereas other are tandem repeated short DNA sequences (which by their nature tend to expand or collapse) and whose function is still elusive.
Not much junk here therefore! the linked paper is total rubbish just for using this term to sensationalise on this issue!
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