Most eukaryotic genes are made up of exons, introns, and various regulatory regions. Exons contain what we call the coding sequence, or the sections where RNA codons are used as a template for protein translation. The introns, on the other hand, are clipped out during messenger RNA maturation.
The vast majority of intron sequence has no sequence dependent function. There is the rare case of functional sequence existing in introns, such as transposons that serve as promoters or microRNA’s, but these make up a tiny percentage of overall intron sequence. For the most part, as long as introns have the correct splicing sequences near the exon junction and don’t have deleterious functions, then intron sequence can be nearly any sequence you want.
Here’s the question. What does ID/creationism predict we will see when we compare the exons and introns of a gene shared between divergent species? If genes are being reused by a designer then what should we expect from the designer when it comes to changing exon and intron sequence, and why should we expect that?
It doesn’t predict anything. If a region is highly conserved, then God must have made it the same in all creatures because reasons. If it’s not highly conserved, then God decided to do that because reasons. Vague gesturing at supposed nested hierarchies in human technology that aren’t really nested hierarchies.
No matter what the result is, they’ll claim that that’s what we should expect from the designer, because ID/creationism is entirely made up of justification after the fact. On the rare occasion that cdesign proponentists actually make a testable prediction it turns out to be falsified.
If ID/Creationists are incapable of spelling out those reasons then they have demonstrated they lack a model and can’t explain what we observe in biology.
i will only add this comment. i think that most introns are actually functional:
if thats true then i see no real difference from exon sequence. it seems that there is also a problem of IC here:
“However, the mere existence of transcribed gene parts, that are free from selective constraints triggered an increase in genetic diversity that eventually led to the gain of many intron-related functions, up to the point that today they are absolutely essential in intron-rich species, as well as in many intron-poor ones”
in addition:
“Many other lineages seem to have gone through phases of massive intron losses, leading to all those present-day intron-poor species”
we realy need to believe that so many introns have been lost while other species retain so many of them? it doesnt sound like common descent but a separated creation.
and we should not forget: “According to this view, the first introns were, indeed, deleterious elements”. so how did they become fixed in the population? the ad hoc explanation just after that: “and their spreading in eukaryotic genomes was possible due to severe population bottlenecks”.
which is the same with evolution (i will not elaborate on that right now, since i elaborated about it few times here in the past). so i see no difference.
A humble suggestion before a game of Brockian Ultra cricket breaks out. Focus on the OP question first and try to define it, rather than arguing right and wrong.
In this sense, @scd is likely very correct - that ID/Cr should view introns as functional.
If species were separately created then what pattern of differences should we see in exons and introns? If you think that exons are similar to each other because a designer reused them, should we expect the same of introns and predict the same level of sequence conservation in introns as we see in exons?
not necessarily for few reasons (for instance, its possible that introns can absorb more changes because their role is less important than exons). but evolution doesnt predict a particular pattern either, so the creation model is no less scientific than evolution here.
Regardless of whether you think most introns today are functional, your reasons given for rejecting their evolution don’t work.
IC isn’t a problem, but a prediction of evolution. We expect many neutral and even deleterious functions to become irreducibly complex and essential over time. It is unavoidable.
The first introns derive from group II self-splicing introns, and hence could removes themselves following transcription.
Their deleterious effect on fitness would come from their effect on reducing transcription rates in genes where they insert, and from the metabolic costs of their replication. All these effects are known to be much weaker in eukaryotes than in prokaryotes. This readily explains why introns are almost entirely absent from prokaryotes(though curiously, the alphaproteobacterial clade from which of mitochondria derive, harbor various types of group II introns). So while many introns were probably (weakly) deleterious to begin with, their effects would have been very weak and largely masked by the effects of drift.
That is one way deleterious mutations can become fixed in a population and that is an observed fact. In fact it is thought that this is one way in which a population can potentially go extinct if it persists at a very small population size for too long, as this creates the conditions wereeven considerably deleterious mutations can accumulate. Do you reject that these population genetic processes are concrete observed realities?
Heck, there are even some creationists who say that the ineffective action of selection against weakly deleterious mutations is why you get stuff like Genetic Entropy. Do you reject genetic entropy too?
Just to help focus this a bit, it would be helpful if ID/creationists would spell out a few things within the model each one of them is using.
Is the vast majority of intron sequence functional?
If there is function, how is that function dependent on the DNA sequence within that intron?
If introns do not have function related to their sequence, then could the same intron sequence be used for the bulk of introns? Would each created kind be created in such a way that orthologous introns would have the same starting sequence? If not, why not? If any sequence would work, then why would a designer change intron sequences when creating a new created kind?
What are the separate creation events? Was there just one fish that then evolved into all the fish today? Was each genus of fish separately created? When were they created in geologic history in relation to other separately created kinds? Were ducks created around the same time as chimps or the common ancestor of apes?
That paper states an outright falsehood already in the abstract. They say:
The intron has been a big biological mystery since it was first discovered in several aspects. First, all of the completely sequenced eukaryotes harbor introns in the genomic structure, whereas no prokaryotes identified so far carry introns.
That is just blatantly false. Introns have been found in both bacteria and archaea.
They obviously function in having signals that direct their excision.
Beyond that, there’s a good experimental question that’s been addressed many, many times: will a cDNA transgene without those introns (nearly all of them that have been tried) rescue a null mutant in mice?
To be fair, in the paper proper they refer to “spliceosomal introns”. They are correct, although I would argue that group II introns are, in a manner of speaking, relatives of spliceosomal introns.
Yeah same, and it’s a very different thing to say there are no introns as opposed to no spliceosomal introns. In either case the introns have to be spliced out.
