Posted: Jul 02, 2019 10:37 am
by Wortfish
Rumraket wrote:Yeah it's a badly worded sentence, as I initially stated. That's still all it is. They don't make it clear that they're talking about stage F in their later Figure 4, not stage C.


Let's take a look at the offending sentence again, shall we?

"We hypothesize that, upon the onset of selective pressure from cold polar marine conditions, duplications of a 9-nt ancestral element in the midst of the four GCA-rich duplicates occurred."

Now, let's look at the descriptions of stages C and F:

(C) A 9-nt in the midst of the four 27-nt duplicates [/b]became the three codons for one AFGP Thr-Ala-Ala unit and underwent microsatellitelike duplication forming a proto-ORF.

(F) Intragenic (Thr-Ala-Ala)n cds amplification, fulfilling the antifreeze function under natural selection.

I think it is fairly obvious that they mean Stage C.

Natural selection is only mentioned in the final step F.


Except that the authors seem to think that there were "selective pressures" at stage C.

So here you are confused having found other people confused by the same sentence. Now you're three people who are confused by a badly worded sentence. Great, that's just further evidence it's a badly worded sentence. Yet there's still nothing in the context of the discussion that contains the sentence in question which suggests they must be talking about stage C.


Read above.

There's no reason to think the authors actually believe selection drove fixation of duplications in an unexpressed noncoding region, that wouldn't make sense and we don't have to assume the authors are so stupid and ignorant they don't know this.


The authors could be confused. In any case, in the absence of selection, there is no reason to think that any of the incremental steps would have been preserved and not lost to subsequent mutations or to random drift.

They should have just added this to remove any confusion:
"We hypothesize that, following acquisition of a transcriptional promoter, upon the onset of selective pressure from cold polar marine conditions, additional duplications of a 9-nt ancestral element in the midst of the four GCA-rich duplicates occurred. As the number of AFGP tripeptide-coding repeats increased, the antifreeze function would become augmented."


They didn't, because they are referring to Stage C and not F.

That's it, then there would have been no confusion. If you read the legend to figure 4 you will see that natural selection is only mentioned in step F.


But "selective pressures" are referred to earlier.