HEREDITY II7 



spring of this cross were all tall, some of them 

 taller than the tall parent. This generation pro- 

 duced from the cross is known as the first hybrid 

 generation. When the seed of this hybrid genera- 

 tion is planted, the plants are partly tall and partly 

 short, but none is intermediate. Tallness and 

 shortness are distinct characters. In the subse- 

 quent breeding of this experiment the short peas 

 gave rise to short peas and the tall ones to tall 

 peas. Because tallness occurred in all of the off- 

 spring of the first hybrid generation, it is said to 

 be dominant over shortness. On the other hand, 

 short peas occurred in the second hybrid genera- 

 tion and this character of shortness is said to be 

 recessive to tallness. When any such cross is 

 made, the peas are either tall or short so that 

 these two characters are in opposition. The one 

 that occurs must have prevented the other from 

 acting and it thus remains dormant. This factor 

 of tallness and shortness is a character that passes 

 entirely to the offspring and is thus known as a 

 unit character. In order that unit characters 

 shall reappear in offspring, they must be repre- 

 sented previously by what is commonly called the 

 genes or determiners in one or both sex cells. 

 These genes are believed to keep their identity and 

 are passed on into the newly formed sex cells in 

 each individual. All of the genes are located in 

 the chromosomes and apparently have the power 



