PHENOMENA OF INHERITANCE 



263 



garded as physiological processes they must be 

 associated with particular structures, since 

 function and structure are inseparable in life 

 processes. What are these units in terms of 

 cell structures and where are they located in 

 the cell? 



We have in the chromosomes, as Wilson 

 especially has emphasized, an apparatus which 

 fulfils all the requirements of carriers of 

 Mendelian factors (Fig. 57). Both factors 



i'eTtilization 

 Union of 

 Simplex Groups 



OO ABCD 



Cleavage 



Duplex Groups 



ABCD abed 



SoTTiatic Divisity. 



Synapsis Seduction Germ CelU 



Division Simplex Groups 



Duplex QrouDs 



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. (From Wilson.) 



