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GORDON E. DICKERSON 



of heterozygote advantage from k to k' , and hence making actual equilibrium 

 q nearer to .5 (i.e., ^ = [1 + k']/2k'). 



If actual equilibrium frequencies for the more favorable allele are generally 

 below (1 + k)/2k in both populations, reciprocal selection will tend to raise 

 both qi and 92 toward (1 + k)/2k, but at an ever decreasing rate, until q 

 chances to go beyond (1 + k)/2k in one of the populations. However, q\ and 

 92 are unlikely to be equal, even when both are smaller than (1 + k)/2k. If 

 qi > q-i, then qi will be closer than qi to (1 + k)/2k and will move faster in 

 that direction (A^i > d^q-y). Consequently gi will become larger than (1 + k)/ 

 2k and direction of Aq2 will be reversed without reducing A^i to zero. Only 



Qj and qj = .75 

 q. and q, = .75 



Fig. 21.5 — Mean performance of crosses (upper) and rates of progress per cycle (lower) for 



homozygous tester (solid lines) and for reciprocal (broken lines) selection when k = 2 and 



q = .75, as qi and ^i approach and qj and ^2 approach 1. 



