338 Morgan. 



The key to the sex ratio is found in a consideration of the 

 egg-gametes of the F^ generation. The two original couples that 

 went in were rM and Rm. Crossing over (i. e., interchange) gives 

 the secondary combinations RM and rm. In the sperm gametes only 

 two classes are possible, since M is sex-linked, and is confined, there- 

 fore, to the female producing sperm. 



The consequences of these relations appear in the F2 generations. 

 The long winged females (two classes) arise from one of the grand- 

 parental or primary couples, and from one of the cross-over or secon- 

 dary couples. This is true also for the miniature females and in the 

 same sense, except that the egg gamete rm enters into the latter and 

 KM into the long. The expectation is equality of numbers, but the 

 miniature females run 257 behind the long females; a result due in 

 all probability to viability. 



In the males, equal numbers of four classes would be expected 

 except for linkage, but owing to the latter the two larger classes 

 should be rM and Rm, or miniature and rudimentary wings. The 

 long-winged males are due to crossing over, and in a sense give a 

 measure of this result; the only difficulty being to determine what 

 to compare these males with to give the ratio of crossing. If we 

 compare them with the miniature males we get the ratio of i to 4. 

 This means that the breaking or crossing over occurs only one time 

 in five or that the long females with the formula RmX rMX should 

 be four times as many as the long males, while the other class of 

 long females (RMX rMX) should be as numerous as the males. If we 

 subtract the estimated number of the last (401) from the total number 

 of females {2216) we get 1815 females, which is 4.5 times the number 

 of the males. 



There are other ways of estimating these ratios or of calculating 

 the results, but for the present purpose the above comparison will 

 suffice to make clear the deficiency of the long males. 



The large number of rudimentary winged males will be noted. 

 The expectation is that they shall be as numerous as the miniature 

 males. They are actually half as numerous, which is a very large 

 ratio for this mutant that is so little viable. 



The reciprocal cross was also made, but the miniature parent 

 males had white eyes which introduces a complication and a possible 

 source of disturbance. I have added the F2 whites and reds together, 

 class to class. As stated, white miniature males were mated to red 



