76 THE EVOLUTION OF LIVING BEINGS. 



or from any other plant. It is the constitution of the 

 pollen, not its source which causes the effect. 



In the second generation the proportions of the 

 differently constituted plants will therefore be I 

 AA : 2 Aa : i aa. 



If each of these plants forms the same number 

 of gametes, say four, we will get 4 A gametes from 

 the A A plant, 4 A gametes and 4 a gametes from 

 the two Aa plants and 4 a gametes from the aa 

 plant so that we get 



8 A 8 a 

 8 A 8 a 



X 



64 AA 64 Aa 



64 Aa 64 aa 



which means the same proportion as in F 2 , viz 

 1 AA : 2 Aa : 1 aa. 



The proportional frequency of the different combina- 

 tions consequently remains the same, in consecutive Ge- 

 nerations, if promiscuous mating takes place. 

 2) The parents differ in several factors. 



In this case the proportions of course must remain 

 the same also in subsequent generations, if the fac- 

 tors are independent in respect to one another, 

 because then, the same applies to each set of two 

 factors, as was calculated above for the set Aa. 



We may therefore conclude: 



Promiscuous mating brings no change in the proporti- 

 anal frequency of the different possible combinations in 

 subsequent generations ; there is no loss of heterozygotes in 



