The ‘junk’ is in large part genes that have been useful in the past but the promoters have been silenced so the genes are never expressed. These promoters can relatively easily mutate or in some cases epigenetically change to reactivate the gene, so on evolutionary timescales it’s a good idea to keep it around, for flexibility.
I don’t know of any experiments doing what you describe—not in vertebrates—but I could very easily have missed it. I know they strip out lots of stuff all the time in viruses for gene therapy, and that’s stuff that’s actually expressed!
There are reasons that the experiment could fail yet the junk dna would nonetheless be junk (containing no information) - if, for instance, self-hybridization is used to splice things, then you’re going to need non-information-bearing DNA to mechanically connect the self-hybridizing areas. That, at least, is not going to approach 90%.
There could be other space-takers that are less removable, especially in reproduction—what if you’re heterozygous with a gene that’s junk in one case and not in the other? Meiosis could be a train wreck if you try to take away that junk gene!
If a gene isn’t being expressed, there’s no way to weed out deleterious mutations. The “keep it around for later” thing might work on short time scales, but on longer time scales genes that aren’t being expressed will degrade into gibberish.
These promoters can relatively easily mutate or in some cases epigenetically change to reactivate the gene, so on evolutionary timescales it’s a good idea to keep it around, for flexibility.
Evolution can’t decide to keep something around just because it might be useful for future evolution. If it’s not currently causing an organism to have more/stronger children (or fewer/weaker), evolution doesn’t pay attention to it.
Also, you’re describing pseudogenes. I don’t think they make up a large part of noncoding DNA, but I don’t have actual numbers.
The ‘junk’ is in large part genes that have been useful in the past but the promoters have been silenced so the genes are never expressed. These promoters can relatively easily mutate or in some cases epigenetically change to reactivate the gene, so on evolutionary timescales it’s a good idea to keep it around, for flexibility.
I don’t know of any experiments doing what you describe—not in vertebrates—but I could very easily have missed it. I know they strip out lots of stuff all the time in viruses for gene therapy, and that’s stuff that’s actually expressed!
There are reasons that the experiment could fail yet the junk dna would nonetheless be junk (containing no information) - if, for instance, self-hybridization is used to splice things, then you’re going to need non-information-bearing DNA to mechanically connect the self-hybridizing areas. That, at least, is not going to approach 90%.
There could be other space-takers that are less removable, especially in reproduction—what if you’re heterozygous with a gene that’s junk in one case and not in the other? Meiosis could be a train wreck if you try to take away that junk gene!
If a gene isn’t being expressed, there’s no way to weed out deleterious mutations. The “keep it around for later” thing might work on short time scales, but on longer time scales genes that aren’t being expressed will degrade into gibberish.
Relevant to this point:
http://www.nature.com/nature/journal/v485/n7396/full/nature10995.html
Evolution can’t decide to keep something around just because it might be useful for future evolution. If it’s not currently causing an organism to have more/stronger children (or fewer/weaker), evolution doesn’t pay attention to it.
Also, you’re describing pseudogenes. I don’t think they make up a large part of noncoding DNA, but I don’t have actual numbers.
Evolution can’t decide to do anything. It occurs that genes that aggressively root out recently abandoned genetic material are maladaptive.