72* 



THE AMERICAN NATURALIST 



[Vol. XLVII1 



2. Linkage Relations 

 (a) Sex Linkage 

 If in the crosses thus far described the sex of parents 

 and offspring that show Beaded wings be considered, it 

 may appear at first as though we may be dealing with a 

 partially sex-linked gene. For it very frequently happens 

 that when the mother is Beaded, and the father is normal 

 (either of Wild stock or of some mutant stock not carry- 

 ing Beadedness), more of the sons than of the daughters 

 are Beaded. For example, in one such brood, there 

 were 17 Beaded to 128 normal females, and 5 Beaded 

 to 130 normal males, or 12 per cent, of the females 

 and 3.5 per cent, of the males. Both of these examples 

 were deliberately chosen because they were good ex- 

 amples of the phenomenon described. It would be possi- 

 ble to select from my records several examples of the 

 reverse phenomenon, where Beaded females had more 

 Beaded daughters than Beaded sons, and where Beaded 

 males had more Beaded sons than Beaded daughters. 

 Nevertheless, the records of all broods available have 

 given the numbers shown in Table VI, where it appears 

 that more sons are Beaded when only the mother is 

 Beaded and more daughters when only the father is 

 Beaded. 



It may perhaps be significant, on the other hand, that 

 when the mother is Beaded a slightly larger percentage 

 of her daughters is Beaded than of the daughters of a 

 Beaded male, while a very much larger percentage of her 

 sons is Beaded than the sons of a Beaded male. In other 

 words, it seems that the daughters are affected to ap- 

 proximately the same extent, whether they get their 

 Beadedness from father or mother, while the sons are 

 affected also by the mother, whether or not she carries 

 Beadedness. This might mean that there is some gene in 

 the sex chromosome that does not show except when other 

 Beaded factors are present. That this is not the case 

 will appear from Chart 2, which records three generations 

 of flies in each of which the mother was normal (Wild) 



