RESULTS OF IRREGULARITIES 



29 



lately or according to specifications. In rare cases, in forming 

 germ cells, the two members of a pair of chromosomes fail to 

 separate (Figure 5, 5). Then one germ cell is formed that has 

 two members of this pair, while another has no member at 

 all of this pair. This gives rise to many further irregularities. 



A 



B 



C 



D 



Parents 



Germ Cells FertLlized Eggs 



Figure 5, Diagram showing how the number of chromosomes some- 

 times becomes changed through irregularities of division. The cell A 

 divides in the usual way, producing germ cells containing one chromo- 

 some from each of the seven pairs. In the division of the cell B, both 

 members of the second pair go to one of the germ cells, which thus has 

 eight chromosomes, while the other germ cell has no chromosome of 

 the second pair. By union of the normal germ cells from A with the 

 changed germ cells from B, as indicated by the arrows, a germ cell C 

 is produced that has three chromosomes of the second pair, and 

 another germ cell D with only one chromosome of the second pair. 



When the germ cell with two chromosomes of a pair unites 

 at fertilization with one of the usual germ cells, an individual 

 is formed that has three chromosomes instead of the usual 

 two (Figure 5, C), for this pair; the genes of this pair are 



