H 



GENETICS 



production of offspring, one of the chromosomes is omitted 

 from some of the cells, though it enters the others. And 

 it was found that this does, indeed, make a very great dif- 

 ference in the nature and characteristics of the offspring 

 produced. 



Concretely, it was found that in the males of many or- 



J 



^ 



il(^€ % % i k 



Figure 3. The male (A) and female (B) groups of chromosomes 

 in a bug, Protenor, after Wilson. At the left in each case is shown 

 the group of chromosomes as it appears under the microscope. At 

 the right are shown the pairs of chromosomes constituting the group, 

 arranged in order of size. X, the X-chromosomes. 



ganisms the number of chromosomes in the cells is odd, 

 while in the females of those same organisms, the number 

 is even (figure 3). The females have one more chromosome 

 than the males, in every cell. The set of chromosomes in 

 the cells of the males is exactly like the set in the females, 



