[For this model, allele A is semi-dominant to allele B, so we use t for selection coefficient]
 

	AA	AB	BB
	W0	W1	W2	qinitial
Island	1	1-t	1-2t	qi  0
Mainland	0	0	1	qm  1

What is the equilibrium frequency f(B) on the island?
     change in f(B) from migration: q_i = m(q_m - q_i)
     change in f(B) from selection: q_i  = -tq_i(1 - q_i)) / (1 - 2tq_i)
                                                                 -tq_i(1 - q_i)                     [if tq_i << 1]
     Then, combined change           q_i = m(q_m - q_i) - tq_i(1 - q_i)
                                                                 = mq_m - mq_i - tq_i + tq_i²)
                                                                 = tq_i² - (m + t)q_i + mq_m

For q_i = 0   this can be solved as a quadratic equation for several special cases:
       if m    t:      q_i    q_m              migration behaves like mutation
       if m >> t:      q_i    q_m                 mainland alleles 'swamp' island population
       if m << t:      q_i    (m / t)q_m       some equilibrium is achieved, if m is constant