Mother 



Daughters 



;^— >; 



xc 



iv'i'''"i''i'r':''--A i 



r^ ^ 



Ei^Smi 



Figure 13. Course of inheritance of white eye and red eye in Droso- 

 phila, when the father has white eyes, and the red-eyed mother has 

 one of the defective X-chromosomes (shown in outline) that tend to 

 produce white eyes. Of the daughters (a and b), one-half (a) receive 

 a defective X-chromosome from both mother and father ; these have 

 white eyes. The other half (b) of the daughters receive a normal X- 

 chromosome from the mother, a defective one from the father ; these 

 have red eyes. Of the sons (c and d) one-half (c) receive the mother's 

 defective X-chromosome and therefore have white eyes ; the other 

 half (d) receive the mother's normal X, and so have red eyes. 



33 



