8 THE METHODS AND 



column of values for these ingredients, but 

 we must rule two columns, one for the ovum 

 and one for the spermatozoon, which united 

 in fertilisation to form that man, and in each 

 column we must represent how that gamete 

 was supplied in respect of each of the in- 

 gredients in our list. When the problem of 

 heredity is thus represented we can hardly 

 avoid discovering, by mere inspection, one 

 of the chief conclusions to which genetic 

 research has led. For it is obvious that the 

 contributions of the male and female gametes 

 may in respect of any of the ingredients be 

 either the same, or different. In any case in 

 which the contribution made by the two cells 

 is the same, the resulting organism in our 

 example the man is, as we call it, pure-bred 

 for that ingredient, and in all respects in 

 which the contribution from the two sides 

 of the parentage is dissimilar the resulting 

 organism is cross-bred. 



