Li: MUTATION, SELECTION, AND POPULATION FITNESS 



43 



Table 5. — Equilibrium Condition when Selection is Against the Recessives.* 



Population 1 



Population 2 



Population 3 



Parameters in nature 



Recessive proportion 

 Average fitness 



u = 0.000,018 

 s = 0.02 



R = 0.0009 



w = 0.999,982 



u = 0.000,045 

 s = 0.05 



R = 0.0009 



w = 0.999,955 



u = 0.000,090 

 s = 0.10 



R = 0.0009 



w = 0.999,910 



Population 4 



Population 5 



Population 6 



Parameters in nature 



Recessive proportion 

 Average fitness 



u = 0.000,050 

 s = 0.02 



u = 0.000,050 

 s = 0.05 



u = 0.000,050 

 j = 0.10 



R = 0.0025 R = 0.0010 R = 0.0005 

 u, = 0.999,950 w = 0.999,950 w = 0.999,950 



*wi = 1 — t; W2 = 1; n/8 = 1 — 5. 



in all three populations. This means, the genetic composition of these 

 three populations are the same at equilibrium. The average fitness of 

 the populations, however, is decreasing from 1 to 3. In populations 

 4-6, the mutation rate and consequently the average fitness of the 

 population is the same, but the recessive proportion R, and thus the 

 recessive gene frequency q, decreases from 4 to 6. 



How do we compare these populations? What criterion should 

 be adopted? What is the value judgment involved here? In some 

 discussions it is implied that a "good" population should have a low 

 frequency of deleterious genes. This seems to suggest that the value 

 of R should be used to compare different populations. If so, then 

 populations 1, 2, 3 are considered to be equally good and 4 is worse 

 than 5 which in turn is worse than 6. In other discussions the average 

 fitness has been adopted as the criterion for judging populations on 

 the theory that w shows the deviation of the actual population from 

 an hypothetical one in which there is no deleterious mutation nor 

 selection (all AA, w x = w = 1). From this viewpoint, populations 

 4-6 are equally good, but 1 is better than 2 which in turn is better 

 than 3. 



The difference between these two criteria is essentially this: R is 

 static in nature, describing the genetic composition of a population, 

 while sR = \—w is dynamic, indicating the amount of selectional 

 turnover in each generation. As an analogy, we may consider two 



