INHERITANCE OF SEX 



<7 



221 



FIG. 98. Diagram illustrating the history of the sex chromosome in the bug 

 Protenor. In the male (cf) there is one large, unpaired chromosome (repre- 

 sented as blank) in A-E'. B, Union of the chromosomes in pairs except the X- 

 chromosome. The two successive maturation divisions (C, Z),) show the dis- 

 tribution of X in the resulting spermatozoa (E, E') , two of the four having X, two 

 having no X. The latter have only five chromosomes and on uniting with eggs, 

 produce only male individuals. The female organisms have two X's which pair 

 in maturation like the other chromosomes so that the resulting eggs and polar 

 bodies all have two X's. A spermatozoon with X uniting with an egg produces a 

 female organism. (From Morgan.) 



