Heredity 



169 



be represented in this manner. For example, RR may 

 represent a plant which has been formed by the union 

 of a red pollen-grain (pollen-grain from a pure red parent) 

 R and a red egg-cell R. This plant if self -fertilized will 

 always remain red. Similarly rr represents a plant 

 which has the absence (or the opposite) of red, say, yellow. 

 If a red plant R were crossed with a yellow plant r, the 

 result would be a hybrid Rr. Red being dominant, the 

 first generation hybrid, F\, would appear as red. 



The following method of squares will be found very 

 convenient to illustrate the action of chance which governs 

 the union of gametes to form the F 2 hybrid plants : 



Square (1) represents a plant (RR) formed from the 

 union of a red pollen-grain R with a red egg-cell R, 

 and is pure red. Square (2) represents a hybrid plant 

 (Rr) formed by r pollen-grain and R egg-cell. Square (3) 



