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 : 1. 

 A schema will make the theory obvious : 



D (tetf)? 



I 



Egg-cell . ft) 



x R (dwarf) <$ 



© . 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 — 



CD 







fe 

 © 



© 







CD 

 © 



© 



© 

 © 

 © 



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 ? 



®o©e©9©© 



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 — 



»Dt 2 «D(R) + »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 1 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 recess ve character R — the germ-cells segregate into two 



