[amirkdv]

> as we have more and more interdisciplinary scientists jumping in at the interdisciplinary level, we're already in an era where diletanttery (especially in trendy science mashups like biophysics) is high

Once heard a bioinformatics (CS) PhD candidate say "natural selection would remove a region of the genome if it didn't have biological function". They graduated with a thesis having to do with genome evolution.

[barry-cotter]

This has to be true over geological time doesn't it? I know about "junk" DNA but as I understand it much of that probably is functional, though it's not expressed in protein. Natural selection is what stops DNA from becoming non-functional. If a goven sequence stops working that means either something breaks and the organism gets sick(er) or a workaround is developed or redundancy is used up. If something is non-functional there are many more ways for it t be non-functional in the same way than one so mutation is far lesss constrained than if it's expressed so over the very long run we should expect non-coding regions to disappear though there will always be quite a few.

Over the extremely long run regions of the genome that have no biological function should disappear, no?

[dnautics]

> Over the extremely long run regions of the genome that have no biological function should disappear, no?

I think the only argument you can make is that 'eventually a neutral deletion would delete it' but I don't think we have a sense of what the timescale of that should be, and anyways, that isn't 'natural selection', unless you have some sort of argument that there is some intrinsic burden to maintaining DNA. If there is such a burden, it's very low, and probably doesn't affect the reproductive fitness of most organisms (esp. not higher organisms).

I think maybe for a really small organism, like on the order of Mycoplasma, or viruses, the carrying extra base pairs burden can be real, but this is not a general rule across biology.

[panabee]

hypothesis: one purpose of "junk" DNA is to guard against viral disruption of coding regions.

even if they serve no purpose except to fill space, the added base pairs create "decoy" areas of DNA and decrease the likelihood of random mutations affecting vital functions.

[amirkdv]

> Natural selection is what stops DNA from becoming non-functional [...] Over the extremely long run regions of the genome that have no biological function should disappear, no?

If you have a sequence that's neutrally mutating with no corrective pressure it won't eventually disappear. At most it'll mutate into something unrecognizable [^1]

For example, your genome is littered with pseudogenes. These are mutated, ineffective shadows of what used to be a functioning gene. Nonetheless they're still close enough to what they used to be that you could reason about them in an evolutionary sense, eg: this one is also a pseudogene in other primates (i.e. it stopped mattering a long time ago), or this other one has a functioning homolog in non-primate vertebrates (i.e. it kept functioning in that lineage).

[^1] as a first order approximation. There are of course other structural events that can create much more change per event than your run of the mill single-point mutations that occur during every DNA replication.