Chromosome Reduction 



253 



tion of this suggestion has come in recent years through a 

 large number of experimental studies. 



Chromosome Reduction 



When a germ cell is formed the cells of the ovary or 

 spermary that are to form gametes divide at first in the way 



Fig 6y. The Ripening of Germ Cells 



The chromosome material passes from a diffused, or at least indistinguishable, stage into 

 a tangle or thread, a, b, that becomes thickened, c, and divides into a definite number of 

 paired chromosomes (three are here shown for the sake of simplicity), d. Each pair of 

 chromosomes divides, one member moving to one pole and one to the opposite pole, e, f. 

 The three chromosomes derived from the father are shown in black, those from the 

 mother in white. The distribution of the chromosomes to the two poles is quite random, 

 but one of each pair goes to each pole, and two daughter cells are formed, g. Each chromo- 

 some then splits lengthwise and the two halves become separated, h, the two cells 

 becoming four, i. Each of these cells now contains one half the number of chromosomes 

 of the original cell, a-d, and one fourth of the chromosome material. From Morgan, 

 The Theory of the Gene, published by Yale University Press. 



