Manchester Memoirs, Vo/. hi. (igi 1-12). 7 



but when crossed the two factors unite, and a coloured 

 form results. In the (/ 2) generation, both white and 

 coloured forms were produced from the coloured cross, 

 indicating that a segregation had taken place in some of 

 the offspring of the two-colour-producing factors, 



Besides dealing with isolated pairs of allelomorphic 

 characters, Mendel experimented also with plants differing 

 in two characters from one another. For these investiga- 

 tions he was also able to use the garden pea. Selecting for 

 one parent a variety characterised by green round seeds, 

 and for the other a form with yellow wrinkled seeds, he 

 obtained a cross, the seeds of which were yellow and 

 round, as these two characters are dominant to greenness 

 and wrinkledness. Allowing the flowers of this first 

 hybrid generation {/ i) to be self- fertilised, he obtained 

 four different types of plants : 



a. Plants with yellow, round seeds (two dominant 



characters). 

 /;. Plants with yellow, wrinkled seeds (one dominant 



and one recessive character). 



c. Plants with green, round seeds (one recessive and 



one dominant character). 



d. Plants with green, wrinkled seeds (two recessive 



characters). 



The numerical ratios of these forms were as 

 9:3 :: 3:1 



for the respective gametes, t.e., egg cells and pollen 

 grains would be of the four types, YR (yellow round), 

 Vif (yellow wrinkled), gR green round, and £';v (green 

 wrinkled), the capital standing for the dominant character. 

 Consequently there would be sixteen possible cross 

 pollinations. These combinations may be graphically 

 represented as follows : — 



