THEORETICAL INTERPRETATION 



345 



cell the primary constituent or factor corresponding to tallness, 

 and three contain the primary constituent or factor of dwarf- 

 ness. Each of these is pollinated by a pollen-grain, which, by 

 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) ? 



I 

 Egg-cell . Q 



X R (dwarf) $ 



x Male-cell. 



Fertilised egg-cell 



This develops into an organism, 

 whose body- cells express the 

 quality " tallness " (D). The 

 germ-cells of the organism 

 segregate into two sets. 



The mature male cells also 

 consist of two sets, with the 

 potential quality of " tallness" 

 or of " dwarfness." What are 

 the chances of fertilisation ? 



The mature egg-cells consist 

 of two sets ; half with the 

 potential quality " tallness," 

 half with the potential quality 

 " dwarfness." 



The result must be 



0009999 

 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 



2 D -f 4 D(R) 4- 2 R ; 

 or more generally 



n D + 2 n D(R) + n R 



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. 



