Posted: Jul 02, 2019 10:50 am
by Rumraket
Wortfish wrote:
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.

It's fairly obvious that they don't, since natural selection isn't mentioned in stage C, only in stage F.

Done, case closed.

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.

Except they don't. Read above.

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.

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.

They could also be unclear. They could be all sorts of things. There's no reason to think they're incompetent, as opposed to just unclear.

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.

The incremental steps before F are a chain of mutations happening by 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.

No, they're referring to stage F and were just being unclear.

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.

Not in the legend to figure 4. When they speak about selective pressure driving fixation of mutations, they're speaking of step F because that's the only point at which selection can operate to fix mutations in the population. There's no reason to think the authors don't know that, and your interpretation is unnecessarily malicious.