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I'm reading a text (Wagner, 2007) on identifying positive selection. In paper, the author says that low complexity regions are known to be associated with relaxed selection. I'm trying to understand why this is true. I get that if the region is under relaxed selection then most mutations would be tolerated but why would that lead to low complexity (other than something like slippage during DNA replication)

It's in the section: "Little overlap between variation clusters and low complexity regions"

Wagner A. 2007. Rapid Detection of Positive Selection in Genes and Genomes Through Variation Clusters. Genetics 176(4): 2451–2463.

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can you provide a link to the text that you are reading so that the context of the author is clear –  WYSIWYG May 3 '13 at 4:11

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Low complexity regions have repeats in nucleotides ( or amino acids ). E.g. PPCDPPPPPKDKKKKDDGPP or AAATAAAAAAAATAAAAAAT. This 2011 article compares 14 individual Plasmodium falciparum genomes and finds that these repeats are highly variable between individuals - some may be short AAAATAAAA others may be longer AAAATAAAAAAAAATAAAAAAATAAAATAAAA....AATAA even to scores of bases.

I think its not clear what these sequences do, but the mere fact that they can vary so much from one viable individual to another indicates that they are not strongly selective. *If they were subject to selection, you would be able to see the difference in the variation in the health, fitness, and reproduction that these significant genetic changes have, but in this case the change in sequence would not change the properties of the sequence much if at all. *

I think these are also related to copy number variable (CNV) regions. which expand and contract in the genome easily even between identical twins. (sorry for the indirect reference - like many SDN stories, the reference is totally wrong), but I remember this work...

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