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This is a paragraph from my textbook.

The significance of such complexities is now beginning to be understood. The split-gene arrangements represent probably an ancient feature of the genome. The presence of introns is reminiscent of antiquity, and the process of splicing represents the dominance of RNA-world. In recent times, the understanding of RNA and RNA-dependent processes in the living system have assumed more importance.

NCERT XII (pg. 111)

I am unable to understand the above sentence in bold. Can anybody explain. Thanks

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    $\begingroup$ I have changed the title so it is more general. This will allow better indexing and make it more likely that it is noticed by people searching the terms splicing and RNA world for general information, rather than wishing to interpret the same phrase in this book. $\endgroup$ – David May 5 '17 at 8:39
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This is a badly-worded phrase that means nothing in the context of the paragraph in which it occurs. There is no way the reader could be expected to understand it from this awful book on its own. Normally I would not think it the role of this site to remedy deficiencies in text books. However, as this involves some interesting questions I will try to read the author’s mind.

The author probably means something like:

“splicing is a relic of the RNA world”

…although a more measured statement would be:

“the existence of self-splicing supports the idea that the current DNA/protein world was preceded by an RNA world”

The author’s use of the word “predominance” is just incorrect English. (Sloppiness or deficient vocabulary.)

An RNA world?

So what is all this about an ‘RNA world’? The author refers to this on p. 104. He states as a categorical fact what it is important to realize is only a theory:

RNA was the first genetic material…RNA used to act as a genetic material as well as a catalyst…

Why is splicing relevant to this? Some types of splicing are catalysed by the RNA itself — self-splicing — an example of an RNA enzyme (ribozyme). From the existence of these and other ribozymes it is argued that originally all enzymes may have been ribozymes, and protein enzymes only developed later, taking over most, but not all enzyme functions.

It is important to realize that RNA preceding DNA, and the first enzymes being RNA rather than protein, are two independent ideas. Although both these ideas are widely held, and I personally tend to favour them, certain scientists have argued strongly against them, as discussed by Harold S Bernhardt.

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  • $\begingroup$ Thnx for your answer. I have accepted it. Can u plz explain that how the “the existence of self-splicing supports the idea that the current DNA/protein world was preceded by an RNA world” $\endgroup$ – San May 5 '17 at 5:35
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    $\begingroup$ @San — As I wrote, the RNA World idea postulates a stage before protein enzymes in which all enzymes were RNA. (Among other things this addresses the chicken/egg problem of protein synthesis discussed in biology.stackexchange.com/questions/43111/…) At a basic level, any contemporary RNA enzyme demonstrates that such a world of non-protein enzymes might have been possible. For more details you should look at the references I have included in my answer. $\endgroup$ – David May 5 '17 at 8:34

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