lo Segregation [ch. 



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

 are considering, to dwarfness. 



But the tall 7% dominants when tested by a study of 

 their offspring (T^g), 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^ 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^ generation therefore, formed by self- 

 fertilisation of the original hybrid consists of three kinds 

 of plants : 



25%. . 50%. 257, 



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 (Z^) 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^ family made up of 



2^DD : 2^DR : 2^RD : 2^RR. 

 ^ '^ ^ : i^. 



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

 fertilisation the resulting individual is in appearance D ; 

 therefore F^ appears as 3/^ : iR. The results of the F.^ 



