THE CHROMOSOME MECHANISM 



Prophase 



Tetrad of Spores or Gsrm Cells 



Fig. 6. — The structural and genctical history at meiosis of two pairs of chromosomes, 

 one partner in each hatched, undergoing crossing-over and segregation. Note that 

 all four products differ in the genetical origin of each of their chromosomes even 

 where only one chiasma has been formed in a bivalent (from Darlington 1945). 



3^ 



