360 BIOLOGY 



or not at all. For example, two varieties of peas are known, one 

 of which has short pods and the other long pods. If they are 

 crossed the offspring are either short-podded or long-podded, 

 but not midway between the two. Very many other characters 

 have been tested out experimentally and found in the same way 

 to be inherited as unit characters. 



Dominant and recessive characters. Mendel's law further 

 points out that some of these unit characters are much more 

 likely to reappear in the offspring than others. It frequently 

 happens that of two opposite characters, one is much more likely 

 to appear in the next generation than the other. Those that 

 are most likely to reappear are called, in this terminology, 

 dominant (Lat. dominari = to rule), while other characters that 

 are more likely to disappear in the first generation, are called 

 recessive (Lat. recessus = receding). These recessive characters, 

 even though they do not appear in the first generation of off- 

 spring, are not necessarily lost. The offspring may contain 

 within its body the germs of these characters, but they may 

 remain dormant, not appearing at all in the first generation. 

 In subsequent generations these recessive characters may re- 

 appear; thus recessive characters, which are present in one gen- 

 eration, may disappear in a following generation, to reappear 

 subsequently in the later generations. 



Law of inheritance. The specially valuable contribution of 

 Mendelism is the formulation of a law in accordance with which 

 these dominant and recessive characters reappear in subsequent 

 generations. That law is briefly as follows: When we cross with 

 each other two individuals, one of which has a dominant char- 

 acter, while the other has its opposite as a recessive character, 

 all of the offspring in the first generation show the dominant 

 characteristics. But although showing only the dominant 

 characters they actually contain a mixture of dominant and 

 recessive characters. This is shown by the fact that if these 

 individuals now are bred together, in the next generation, which 

 we will call the second generation, only three-fourths of the off- 



