262 



HEREDITY AND ENVIRONMENT 



function as well as in structure. And there is 

 no reason to doubt that if we had sufficiently 

 powerful microscopes we should find still 

 smaller and smaller units until we came at last 

 to molecules and atoms. 



The fact that inheritance units from the 

 two parents unite in fertilization and later 

 segregate in the formation of gametes, so that 

 the latter are pure with respect to any char- 

 acter, is a familiar part of Mendelian inheri- 

 tance (Fig. 56). Even if these units be re- 



FIG. 56. Diagram showing union of factors in fertilization 

 and their segregation in the formation of germ cells. With 

 4 pairs of factors (Aa, Bb, Cc, Dd) 16 types of gametes are 

 possible as shown in the two series of small circles at the 

 right. (From Wilson.) 



