220 



THE PERPETUATION OF ADAPTATIONS 



of the pair comes from the female parent, the other from the 

 male. Mendel crossed two types of garden pea, one parent 

 plant producing yellow peas, the other green peas. A hybrid 

 (Fi generation) resulted from this cross, which produced only 

 yellow peas. These yellow peas produced plants which were 



PARI N S 



FIG. 93. Mendelian inheritance resulting from the crossing of yellow and green 



peas. (From Morgan,) 



then intercrossed or self-fertilized, and the resulting peas (F2 

 generation) were found to be mixed, the pods containing both 

 yellow and green peas in the proportion of three yellow to one 

 green (Fig. 93). These, in turn, were grown and again self- 

 fertilized, when it was found that the green peas produced only 



