HEREDITY 139 



green seeds. They were planted for several generations 

 and always came true, showing no yellow character. 

 When the yellow seeds were planted, however, Mendel 

 found that a certain proportion of the yellow seeds had 

 both green and yellow offspring and a certain proportion 

 had only yellow offspring. The latter remained fixed 

 and true in character when bred for several generations. 

 The results of these investigations carried through 

 many generations indicated that there was a certain 

 mathematical ratio traceable in the offspring resulting 

 from the crossing of these two distinct varieties of peas. 

 In these results Mendel found that in the first genera- 

 tion the dominant character (yellow seed) appeared to 

 the exclusion of the green color. In the second genera- 

 tion he found that 25 per cent of the offspring were green 

 and 75 per cent apparently yellow. If the green peas 

 were planted, they produced only green peas, but when 

 the yellow peas were planted, they produced 25 per cent 

 pure yellow, 50 per cent mixed or hybrid (yellow and 

 green), and 25 per cent pure green. The pure yellows 

 and pure greens continued to breed true, but the 50 per 

 cent " hybrid " peas continued to split up in each genera- 

 tion in the proportions of 25 per cent pure green, 25 per 

 cent pure yellow, and 50 per cent hybrid. 



132. The law of dominance. From these results 

 Mendel formulated the law of dominance, which is that 

 when two contrasting characters are bred together the 

 offspring in the first (Fi) generation will all exhibit the 

 dominant character. 



133. The law of segregation. When the individuals 

 comprising the first generation are interbred, the resulting 

 offspring (F 2 generation) will possess the characters in 

 the proportion of three of the dominant character to one 



