58 INBEEEDING AND OUTBEEEDING 



The total number of plants in the F 3 generation is not 

 quite the same as the F 2 generation due to seed not 

 germinating or plants dying, but it is plain that the ratio 

 of SAB : 3aB : 3Ab : lab obtained in the F 2 generation 

 is made up of the following actual classes : 



1 AABB 



9 apparently AB made up of AABb 



4 AaBb 



3 apparently Ab made up of j* ^ 



(1 aaBB 

 3 apparently aB made up of 



1 apparently ab made up of 1 aabb 



The four classes AABB, aaBB, AAbb and aabb, hav- 

 ing each factor in the duplex condition bred true; the 

 heterozygous condition of one or both allelomorphs 

 in the remainder was shown by the character of the 

 F 4 progeny. 



In order to visualize these facts, or in truth the facts 

 from any number of pairs of allelomorphs in independent 

 Mendelian inheritance, one has only to recall that pairs 

 of homologous chromosomes one paternal and one ma- 

 ternal meet during the process of gametogenesis and 

 one or the other of each pair passes to either daughter 

 cell. The factors A and a lie in corresponding loci in 

 one pair of chromosomes, the factors B and b lie in cor- 

 responding loci in a second pair from among the seven 

 paired chromosomes of the garden pea. Thus gametes 

 bearing the factors AB, Ab, aB and ab will be formed in 



