io Segregation [CH. 



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

 are considering, to dwarfness. 



But the tall /% 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 F 3 consisting of both 

 tails and dwarfs, the proportion showing again an average 

 of three tails to one dwarf. 



(b] 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 F z generation therefore, formed by self- 

 fertilisation of the original hybrid consists of three kinds 

 of plants : 



o / o / o / 



2 5 /o. 50 / 2 5 /, 



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 bearersHof 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 F z family made up of 



But, as th,e first cross showed, when D meets R in 

 fertilisation the resulting individual is in appearance D ; 

 therefore F^ appears as $D : iR. The results of the F z 



