346 EXPERIMENTAL STUDY OF INHERITANCE 



hypothesis, contains the potential quality of tallness or of 

 dwarfness ; and if the two kinds of pollen-grains are present 

 in equal numbers, each ovule has an equal chance of being 

 fertilised by a pollen-grain with a potential quality of tallness 

 or by a pollen-grain with a potential quality of dwarfness. 

 Therefore the result must be a set of offspring partly dominant 

 and partly recessive, in the proportions of 3 : I. 

 A schema will make the theory obvious : 



D (tall) ? 

 Egg-cell . 



x R (dwarf) $ 



x . Male-cell. 



Fertilised egg-cell 



The mature egg-cells consist 

 of two sets ; half with the 

 potential quality " tallness," 

 half with the potential quality 

 " dwarfness." 



The result must be 



This develops into an organism, 

 whose body-cells express the 

 quality " tallness " (D). The 

 germ-cells of the organism 

 segregate into two sets. 



<D ' 



The mature male cells also 



0) consist of two sets, with the 



^ potential quality of " tallness" 



Q or of " dwarfness." What are 



the chances of fertilisation ? 









*. 

 >*&*' 



& 



-\ ' 



i.e. 2 with the quality of tallness ; 



4 with the qualities of tallness and dwarfness ; 

 2 with the quality of dwarfness. 

 In other words 



2D + 4D(R) + 2R; 

 or more generally 



wD + 2wD(R) + wR 



But as the D(R) offspring are not distinguishable from the D offspring, 

 until further breeding shows that they carry the recessive character 

 in latent form, the proportion is 



3 dominants to i recessive. 



Thus, Mendel assumed that in the hybrid D(R) between a 

 parent with a dominant character D and a parent with a homo- 

 logous recessive character R the germ-cells segregate into two 



