12 MENDELISM 



How did Mendel explain these results ? Here he 

 showed his genius. He assumed that these hybrids — 

 D[R] — produce two kinds of germ-cells in each sex, 

 two kinds of pollen grain, and two kinds of ovules. One 

 kind possesses the dominant character derived from the 

 dominant parent, the other kind possesses the recessive 

 character of the recessive parent. In other words, the 

 dominant and the recessive properties of the parents are 

 conveyed to separate germ-cells of the hybrid. No single 

 germ-cell can carry both dominant and recessive properties. 

 The germ-cells are not hybrids, though the individuals 

 that produced them may be. This is' what Mendel called 

 Segregation and it is the most characteristic of his theories. 



The Germ-cells produced by a dominant parent are 

 all purely dominant ; those of the recessive parent are all 

 purely recessive ; and of those produced by the hybrid, 

 some are dominant and some are recessive. If the dominant 

 is represented by a black circle and the recessive by a white 

 one, then the dominant parent and its germ-cells can be 

 diagrammatically illustrated thus — 



D 



i i I i 



• • • • 



The recessive thus — 



R 



i 



I I ! I 



o o o o 

 The hybrid thus — 



D[R] 



! 



I I I I 



• • o o 



There is only one kind of germ-cells in the dominant, 

 one kind in the recessive, but there are two kinds in the 

 hybrid. 



