

INHERITANCE OF SEX 



221 



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

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

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

 ciromosome. ^The two successive maturation divisions (C, Z>,) show the dis- 

 t ibution of X in the resulting spermatozoa (E, jE'),twoof 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 

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

 female organism. (From Morgan.) 



