Posted: Jul 04, 2019 7:12 am
by Rumraket
The authors have responded and I got permission to post the following from our email exchange:

The upshot is, your interpretation is correct.

The initial duplication of the 9-nt (Fig. 4C) was almost certainly random. There were five GCA repeats already at the site embedded within any of the 27-nt sequence copies (Fig. 3D). Short repeats are prone to expansion as we well know.

For expansion of a functional AFGP coding region as depicted in Fig. 4F to occur, it had to be driven by natural selection, which was indicated in the figure legend (and in the main text). This is the context for the sentence in question.

The paper structured the description of the evolutionary process by genic component. The section on the formation of AFGP coding sequence containing the sentence in question preceded the section on functionalization. I can see how the location of that sentence could lead to mis-interpretation if one does not consider the multiple components holistically.

The alternate sentence you suggested indeed would make it more clear.