of Heredity 19 



may call the parent individuals A and a, and the resulting 

 zygote A a. What will the structure of Aa be in regard to 

 the character we are considering ? 



Up to Mendel no one proposed to answer this question 

 in any other way than by reference to the intensity of the 

 character in the progenitors, and primarily in the parents, 

 A and , in whose bodies the gametes had been developed. 

 It was well known that such a reference gave a very poor 

 indication of what Aa would be. Both A and a may come 

 from a population consisting of individuals manifesting the 

 same character in various intensities. In the pedigree of 

 either A or a these various intensities may have occurred 

 few or many times. Common experience leads us to expect 

 the probability in regard to A a to be influenced by this 

 history. The next step is that which Gallon took. He 

 extended the reference beyond the immediate parents of 

 Aa, to its grandparents, great-grandparents, and so on, and 

 in the cases he studied he found that from a knowledge of 

 the intensity in which the given character was manifested 

 in each progenitor, even for some few generations back, a 

 fairly accurate prediction could be made, not as to the 

 character of any individual Aa, but as to the average 

 character of Aa's of similar parentage, in general. 



But suppose that instead of individuals presenting one 

 character in differing intensities, two individuals breed 

 together distinguished by characters which we know to be 

 mutually exclusive, such as A and B. Here again we may 

 speak of the individuals producing the gametes as A and 

 J9, and the resulting zygote as AB. What will AB be 

 like ? The population here again may consist of many like 

 A and like B. These two forms may have been breeding 

 together indiscriminately, and there may have been many 

 or few of either type in the pedigree of either A or B. 



22 



