Payne: Variations and Selection 



27 



In Table IX the selection line female was crossed to a sepia spineless 

 kidney sooty rough male, and the Fi male back-crossed to a sepia spine- 

 less kidney sooty rough female. Four types of flies appear in ¥2. The 

 distribution of the bristles in these four types is given. 



it. The distribution of the other three chromosomes from the 

 selection Hne is a random one. It is possible for all of them, 

 or any two of them, or any one of them, or even none of 

 them to pass into the same cell with the X-chromosome. All 

 the eggs of the sepia spineless kidney sooty rough females 

 will be alike. Taking up each class of flies which appears in 

 Fo and analyzing it separately, we find the normal females get 

 one X-chromosome from the selection line and ^one from the 

 other. They may get one member of each of the second, 

 third, and fourth pairs from the selection line. Of course, 

 they may get none of them or any two or any one. The sepia 

 spineless kidney sooty rough females also get one X-chromo- 

 some from the selection line and one from the sepia spineless 

 kidney sooty rough line. They must get both third chromo- 

 somes from the sepia spineless kidney sooty rough line, but 

 may get one member of each of the second and fourth pairs 

 from the selection line. The normal males will get their 

 X-chromosome from the sepia spineless kidney sooty rough 

 line, but may get one member of each of the second, third, 

 and fourth pairs from the selection line. The sepia spineless 

 kidney sooty rough males get their X-chromosome and both 

 third chromosomes from the sepia spineless kidney sooty 

 rough line. They may get one member of each of the second 

 and fourth chromosome pairs from the selection line. The 

 interesting fact is that the normal males and females and the 

 sepia spineless kidney sooty rough females have extra bristles, 

 while all of the sepia spineless kidney sooty rough males have 

 the normal bristle number. In these males the X-chromo- 

 some and both third chromosomes come from the sepia spine- 

 less kidney sooty rough line. In the other three classes either 

 one of the X-chromosomes or one member of the third pair 

 from the selection line may be present. Since extra bristle 

 number is partially dominant to the normal, extra bristles 

 would be expected in these classes if the genes for extra 

 bristles are in the first and third chromosomes. On the other 

 hand, if these genes are present in the X-and third chromo- 

 somes, no extra bristles would be expected in the sepia spine- 

 less kidney sooty rough males. I do not mean to say that this 



