Derivation of the Incomplete Dominance case of the General Selection Model
 Given:    genotype:      AA          AB         BB
            phenotype:      W0       W1       W2
                     or           1-s1       1         1-s2
 
  Recall from the numerator of the General Selection Equation that

       q     [(q)(W2 - W1) + (p)(W1 - W0)] 

 So, to find q at equilibrium () (read as, "q hat") where  q = 0

 set     0   = [(q)(1 - s2 - 1) + (p)(1 - 1 + s1)]
        
             = -s2q + s1p

             = s1(1 - q) - s2q

             = s1 - s1q - s2q

  Then    s1 = s1q + s2q = (q)(s1 + s2)

   and    =  (s1)/(s1 + s2)
Optional homework: re-derive the above for "p" at equilibrium 
Text material © 2005 by Steven M. Carr