MENDELISM 45 



other two split up. Thus, of the whole series of grand- 

 children exhibiting the 3 to I ratio, half, when bred to- 

 gether or self-fertilized, came true, and half gave 3 to 

 i again. The half coming' true consisted of one domi- 

 nant and one recessive out of each four ; the other half, 

 of two dominants. 



In discussing such experiments, we now call the 

 original cross, or parental generation, P ; the following, 

 or filial generations, /\, F 2 , F 3 , etc. It must not be 

 forgotten that these terms are purely relative ; the P 

 represents the FI of its parents, the F 2 of its grand- 

 parents, and so forth. 



The characters which act as opposites in inheritance, 

 in the manner described, are said to be allelomorphic. 



7. The principal facts brought out by the experi- Determin- 

 ments have now been described, but how may they be 



explained ? Mendel observed that the characteristics ment give 

 studied were inherited as units, and when he used characters 

 plants having two pairs of opposite characters, he saw 

 that the inheritance of one pair was independent of the 

 inheritance of the other. That is to say, there was no 

 connection between size and the color of the seed, or 

 between the color of the seed and its smooth or wrinkled 

 surface. There was a connection between the color of 

 the seed coat (white or gray to brown) and the color of 

 the flowers, however. Obviously the inherited thing is 

 not a particular color or size or surface, but something 

 which so acts in development as to produce these 

 effects. This something, which may be called a de- 

 terminer, may produce only one visible effect, or many. 

 In the examples cited in the preceding paragraphs there 

 was only one effect considered or noted for each de- 

 terminer. Of each pair of opposites only one can ap- 

 pear in a given individual ; but if there are several 



