io Segregation [CH. 



be pure to the recessive character, namely, in the case we 

 are considering, to dwarfness. 



But the tall F* dominants when tested by a study of 

 their offspring (/%), instead of being all alike (as the dwarfs 

 or recessives were), proved to be of two kinds, viz. 



(a) Plants which gave a mixed 7% consisting of both 

 tails and dwarfs, the proportion showing again an average 

 of three tails to one dwarf. 



(&) Plants which gave tails only and are thus, pure to 

 tallness. 



The ratio of the impure (a) plants to the pure (b) plants 

 was as 2 to i. 



The whole /% generation therefore, formed by self- 

 fertilisation of the original hybrid consists of three kinds 

 of plants : 



25%. 50% 25% 



pure dominants impure dominants pure recessives 

 or 3 dominants : i recessive. 



Segregation. Allelomorphism. 



The conclusion which Mendel drew from these observa- 

 tions is one which will suggest itself to any one who reflects 

 on the facts. The result is exactly what would be expected 

 if both male and female germ-cells of the cross-bred F^ were 

 in equal numbers bearers of either the dominant (D) or 

 recessive (R) character, but not both. If this were so, and 

 if the union of the male and female germ-cells occurs at 

 random, the result would be an ./% family made up of 



3/> : iR. 



But, as the first cross showed, when D meets R in 

 fertilisation the resulting individual is in appearance D ; 

 therefore F 2 appears as $D : iR. The results of the F t 



