The Making of Species 



offspring. Or the D gamete from one parent 

 may unite with a T gamete from the other 

 parent, and the result will be a TD cross, but 

 this, as we have seen, will grow up to look like 

 a pure T, i.e. will become a tall organism. 

 Similarly, a T gamete from one parent may 

 unite with a T gamete of the other, and produce 

 a pure tall form, or it may unite with a D and 

 produce a hybrid TD, which gives rise to a 

 tall form. Thus the possible combinations of 

 offspring are DD, DT, TD, TT, but all these 

 three last contain the dominant T gamete, and 

 so develop into tall offspring ; therefore, ex 

 hypothesi, we shall have three tall forms pro- 

 duced to one dwarf form, but of these three 

 tall forms two are not pure, and do not breed 

 true. Mendel's experimental results accorded 

 with what we should expect to obtain if the 

 above explanation were correct. Hence the 

 inference that there is such a splitting of the 

 gametes in the sexual act seems a legitimate one. 

 Mendel's experiments are of great import- 

 ance, for they give us some insight into the 

 nature of the sexual act. But, as is usual 

 in such cases, Mendel's disciples have greatly 

 exaggerated the value and importance of his 

 work. It is necessary to bear in mind that 

 Mendel's results apply only to a limited 

 number of cases to what we may call balanced 

 characters. In the case of characters which 



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