156 APPENDIX I 



passes from 2-8 % to 11-1 % of the population in 36 generations, 

 and from 11-1 % to 25 % in a further 16 generations — i.e. under 

 a 10 % selection rate in its favour the proportion of the 

 recessive rises from 2-8 % to 25 % in 52 generations. 



If the favoured variety is dominant it must be borne in 

 mind that it can be either homozygous or heterozygous — that 

 for these purposes it is represented in the left-hand column by 

 the hybrids as well as by the homozygous dominant. In a 

 population in equilibrium which contains about 2 % of a 

 dominant form, the great bulk of these dominants will be 

 heterozygous, and the relative proportion of recessives, hetero- 

 zygous, and homozygous dominants is given in the second line 

 of the left-hand column. 



Let us suppose now that we want to know what will be 

 the percentage of dominants after 1000 generations if they 

 form 2 % of the population to start with, and if, during 

 this period, they have been favoured with a 1 % selection 

 advantage. After 165 generations the proportion of recessives 

 is 90-7, so that the proportion of dominants has risen to over 

 9 % ; after 153 further generations the percentage of dominants 

 becomes 27-7 + 2-8 = 30-5; after 739 generations it is 88-8 %, 

 and after 1122 generations it is 69-0 -f 27-7 = 96-7. Hence 

 the answer to our question will be between 89 % and 97 %, 

 but nearer to the latter figure than the former. 



Mr Norton has informed me that the figures in the table 

 are accurate to within about 5 %. 



