A Modification of the Sex Ratio, and of other Ratios, ttc. 



341 



white female combinations comes from an original coupling so that 

 the class is more numerous than the miniature red female class; and 

 the miniature white male class likewise results from an original 

 coupling. It runs behind the white females because only one class 

 enters into the result. (4) The noticeably large number of rudi- 

 mentary red males is due to an original coupling, while the smaller 

 white rudimentary male class is due to a cross-over in the color 

 producer. (5) Conversely, the rudimentary-miniature reds (34) are 

 less than one-half as numerous as the rudimentary-miniature whites. 

 The former calls for a more difficult crossing over, while the latter 

 for a simpler one, on my assumption of the linear arrangement of 

 the factors in the chromosome. (6) Some information is gained 

 concerning the linkage of c (or c) and R (or r) and M (or m). For 

 example, miniature white ö (S are to red d cJ as 633 to 377 or 1.7 

 to I. In order to produce this result, c must cross over from R and 

 m to the other chromosome. Rudimentary red ö is to white d as 

 344 to 148 or 2.3: I and in order to produce this result c must cross 

 over from r and M, as shown in the analysis. These statements mean 

 only that c and c have crossed over, but since this occurs when the 

 polar body forms, only one of the resulting combinations survives 

 each tijne. On the average, i. e., on chance, one should expect one 

 combination to be as frequent as the other. 



The reciprocal cross, rudimentary red females to miniature white 

 males was also carried out. The offspring were, as stated, largely 

 females (long-winged red-eyed); the few males were rudimentary (red- 

 eyed). These mated gave the following results: 



Red. White. 



L5 L9 .M(5 M9 R(J R9 R.-m.(J | l,d 1^9 ^I (5 M9 R c5 R9 R.-m.c5 

 i88 1 130 254 o 249 262 lo 39 o 500 o 93 o 54 



The analysis follows: 



CRmX CKmX Rud. Red 9 

 crMX crm Min. white (5 



Fl 



CRmXcrMX Long Red 9 

 CRmXcrm Rud. Red (J 



CRMX — CRmX — crMX — crmX 1 

 Gametes ..f F, . . . \ cRMX — cRmX — CrMX — CrmX ( ^^ 

 CRmX — crm Sperm 



....{ 



