PHENOMENA OF INHERITANCE 



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- 

 garded as physiological processes they must be 

 associated with particular structures, since 

 function and structure are inseparable in life 



Fertilization 

 Union of 

 Simplex Groups 



OO ABCD 



Cleavage 

 Duplex Groups 

 ABCD abed 



Somatic Divisi 



AbcD 

 Reduction Germ Cells 



Division Simplex Groups 



Duplex Groups 



Fig. 57. Diagram of germ cells corresponding to Fig. 56, 

 showing the union of maternal chromosomes (ABCD) and pa- 

 ternal ones (abed) in fertilization, their distribution in cleav- 

 age, their union into 4 pairs (Aa, Bb, Cc, Dd,) in synapsis 

 and the separation of the pairs in the reduction division. 

 Only 2 of the 16 possible types of germ cells are shown at the 

 lower right. (After Wilson.) 



