deleterious mutation

Glémin S 2003 How are deleterious mutations purged? Drift versus nonrandom mating. Evolution 57:2678-2687.

• the higher |Δx|, the more deleterious alleles should be eliminated
• purging by drift is thus possible if |Δx|_drift ≥ |Δx|_∞
• |Δx|_drift ≥ |Δx|_∞ is true if |Δx| is a convex (i.e., curved upward) function of x

• the reverse is expected for a concave function (curved downward)

• if x is low and spans the convex part of |Δx|x|, moderate variance in allele frequency will enhance selection
• this is typically the case for strongly deleterious alleles
• |Δx|x| is convex for a wide range of x values such that, even with substantial drift, x always varies in the convex part of |Δx|x|
• in the special case of strictly lethal alleles (s = 1), |Δx|x| is always convex
• an intuitive explanation for the fact that lethals are always maintained at lower frequency in small populations than in large ones (Nei 1968; Hedrick 2002)