Uother 



Father 



Daughters 



fr.'.-U.'.'.V.'."..'* 



tons 



9 



r^^ 



c 



D X 





A 



V ri[--iii-i-;i'.d 



Figure 12. Course of inheritance of a recessive character (white 

 eyes) that is dependent on a defective X. The mother has one de- 

 fective X-chromosome (shown in outline), derived from the white- 

 eyed mother of figure 11, her other X-chromosome being normal; she 

 therefore has normal red eyes. The father has a normal X-chromo- 

 some (black), and normal red eyes. Of the four types of offspring 

 shown (a, b, c, d), only one (c), representing half the sons, have the 

 white eyes, this being the consequence of their receiving the mother's 

 defective X-chromosome. All the daughters (a and b) and the other 

 half of the sons (d) have normal red eyes, since they contain at least 

 one of the normal X-chromosomes. 



31 



