MendeW Law 39 



matter what other characters the i)arent-plants may have 

 had. In other words, the characters are independent 

 units, unaffected by other characters or units. The 

 character of tallness from a tall plant with wrinkled 

 seeds or purple flowers will act just the same as from a 

 tall plant with smooth seeds or white flowers. 1\illness 

 is a unit, and its behavior in inheritance is independent 

 of all other units. 



2. Dominance. — In the germ plasm there are certain 

 determiners of unit characters which dominate during 

 the development of the body, causing these characters 

 to dominate over others and thus become visible. The 

 characters dominated over and thus not allowed to 

 express themselves are called recessive characters. These 

 recessive characters may be present in the germ plasm, 

 but cannot express themselves and become \'isible as 

 long as the dominant characters are present. When a 

 dominant character is absent, however, its recessive 

 alternate is free to express itself and become \'isible. 



For example, in the case of tall and dwarf peas, tall- 

 ness is a dominant character and dwarfness is its alter- 

 native recessive. When a dwarf appears, therefore, 

 there is present no dominant tallness to suppress it. 

 In the Fi generation all the individuals were tall because, 

 although they had all received the recessive character 

 of dwarfness from one of the parents, they had received 

 the dominant character of tallness from the other i)arent, 

 and so dwarfness did not appear in an}- of them. Such 

 pairs of alternative characters are now commonly called 

 atlelomorphs. Thus tallness and dwarfness are allelo- 

 morphs in the pea, one dominant over the other, which 

 is therefore recessive. 



