226 GENERAL BIOLOGY 



given. Secondly, these two " units characters " 

 bear some relation to each other, such that one may 

 be suppressed, as it were, and fail to develop in a 

 given generation, and, at the same time, be passed 

 on to another generation, there to become manifest. 

 Characters that are thus linked together in couples 

 have been called by recent investigators " allelo- 

 morphs." Tallness and dwarfness in peas are there- 

 fore hereditary qualities that fall in the category 

 we have already called alternative inheritance. 

 Since, in the presence of the former, the latter is 

 unable to manifest itself, Mendel used the adjective 

 dominant for the tall character, and recessive for the 

 dwarf. A diagram will serve to make this clearer. 

 T indicates the tall character, D, the dwarf character, 

 the parenthesis denoting the recessive or latent 

 condition of the character. The first hybrid genera- 

 tion is called the filial generation, F, the second, F 2 , 

 and so on. 



In considering the F 2 generation, in which the 

 dwarf character reappears, it is also evident that 

 there are two classes of tails. For subsequent 

 breeding '(always with self-fertilization) shows that 

 whereas one third of the tails, like the dwarfs, always 

 breed true, the other two thirds (one half of the whole 

 number) contains the dwarf character in a latent 

 or recessive form, since the latter reappear again 

 in the same ratio, 3 : 1, as that of the previous genera- 

 tion. 



If we assume that the gametes, whose fusion pro- 

 duces the zygote and hence determines the characters 



