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I encountered the term selective constraint in Huber et al. 2015, page 4 (last paragraph) in:

If invariable sites are included in the analysis, then both the methods of Kim and Stephan (2002) and Nielsen et al. (2005) may be sensitive to assumptions regarding selective constraint and mutation rates.

but the context does not quite help.

What it the definition of selective constraint?

Does it has to do with lethal mutations in non-coding regions? Does it has to do with selection interference?...

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    $\begingroup$ Please use the quote environment instead of the code environment (as far as I know most screen readers will start reading this character-by-character). $\endgroup$
    – Willem Van Onsem
    Sep 17, 2015 at 21:43

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It is selective pressure that determines and limits the number of neutral/beneficial mutations that can take place. The more constrained a locus is under selection, the easier it is to generate deleterious mutations and the harder it is to generate beneficial ones; this can be reflected in low substitution rates at such loci in populations with time.

One widely used method to measure this is to compute the Ka/Ks ratio to infer if a locus is selectively constrained or not.

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  • $\begingroup$ +1 Thank you. Can we associate a value to this concept? For example the selective constrained could be $S = K_a/K_a$ or $S = mu_b/mu_d$, where $mu_b$ and $mu_d$ are the beneficial and deleterious mutation rates, respectively. $\endgroup$
    – Remi.b
    Sep 17, 2015 at 22:44
  • $\begingroup$ It is easier to measure Ka and Ks , so if something is under no selection (neutral) you'll see a ratio of 1 , less than 1 indicates purifying selection, more than 1 indicates positive selection. More here cs.mun.ca/~banzhaf/papers/ppsn08_evorate.pdf $\endgroup$
    – Ankur Chakravarthy
    Sep 17, 2015 at 23:36

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