RESULTS OF IRREGULARITIES 



31 



away one chromosome in different cases from each of the 

 twelve different pairs. Many of these twenty-four different 

 varieties have been produced and studied by Blakeslee and 

 his associates. 



In a similar way, two of the pairs may have a third member 

 added to them. For twelve chromosomes, there are sixty-six 

 different ways in which this can be done. This gives sixty-six 

 other differing varieties, many of which have been produced 

 and identified. And there are sixty-six other varieties pro- 

 ducible by subtracting one chromosome from two pairs, in 

 the sixty-six possible combinations of two from twelve. 



When individuals with three chromosomes in place of 

 one of the pairs produces germ cells, some of these germ 

 cells have two chromosomes of that pair, others but one 

 (see Figure 6). When two germ cells unite, each con- 



Parents 



Germ Cells Fertilized Egg 



Figure 6. Diagram of the method by which there are produced indi- 

 viduals with four chromosomes in place of one of the pairs (in this 

 case the second pair, counting from the left). 



