I THE PROBLEM 7 



among those that spring from the same individual. At 

 present our only way of appreciating those differences 

 is to observe the properties of the zygotes which they 

 form. And as it takes two gametes to form a zygote, we 

 are in the position of attempting to decide the proper- 

 ties of two unknowns from one known. Fortunately the 

 problem is not entirely one of simple mathematics. It 

 can be attacked by the experimental method, and with 

 what measure of success will appear in the following 

 pages. 



