272 BIOLOGY: GENERAL AND MEDICAL 



duce the sexual cells through the combination of which 

 the offspring arises, the two parental characters leave each 

 other and enter separately into the sexual cells. From 

 this it may be seen that one-half of the pollen cells will 

 have the quality of one parent and the other the quality 

 of the other. And the same holds good for the egg cells. 

 Obviously, the qualities lie latent in the pollen and in the 

 egg, but ready to be evolved after fertilization has taken 

 place." 



According to Mendel's law, the unexpected appearance 

 in the offspring of characters not found in any but remote 

 parents may be accounted for by the presence of recess- 

 ive allelomorphs which have not until the present 

 generation been able to escape the dominance of the 

 opposed character. 



Mendel's discoveries regarding dominance are of the 

 greatest importance to every student of the problems 

 of heredity and are well synoptized by Castle thus: 



1. "The offspring of two parents, differing in respect of one 

 character, all resemble one parent and therefore possess the 

 dominant character, that of the other parent being recessive or 

 latent. 



2. "In the place of simple dominance there may be manifest 

 in the intermediate hybrid offspring an intensification of character 

 or a condition intermediate between the two parents; or the off- 

 spring may have peculiar characters of their own (heterozygotes) . 



3. "A segregation of the characters united in the hybrid takes 

 place in their offspring so that a certain per cent, of these offspring 

 possess the dominant character alone, a certain per cent, the 

 recessive character alone, while a certain per cent, are again 

 hybrid in nature." 



When the attempt is made to follow a number of Men- 

 delian characters at the same time, the whole matter 

 becomes extremely complicated. 



When hybrids result from combinations of totally 

 different species they are usually infertile, have no 

 progeny, and so die without affording an opportunity 

 for the Mendelian law to be operative. 



It is sometimes difficult to prejudge what characters 

 may be subject to the Mendelian law. Thus whiteness 

 and color are Mendelian characters among most plants 



