A Modification of the Six Ratici, and of otluT Ratios, etc. ßßl 



RMXRmX Long 9 



RmXRmX Rudimentary 9 



rMXRmX Long 9 



rmXRmX Rudimentary 9 



RMXrm Long <5 



RmXrm Rudimentary (J 



rMXrm Miniature (5 



rmXrm Rudimentary-miniature (5 



In this reciprocal cross also there are only two classes of females 

 in F2, these being long and rudimentary winged. There are four 

 classes of males, viz., Long, Miniature, Rudimentary, and Rudimentary- 

 miniature. 



Ignoring for the present the apparently wide discrepancy between 

 the realized and the expected ratios, and emphasizing only the 

 appearance of the expected classes, something further must be said in 

 regard to a new class that has appeared in both of the last two 

 crosses, viz., the na class or rudimentary-miniature wings. 



This class is due to "permutation", and is characterized by two 

 absences. It may seem, on first thought, that no wings at all should 

 appear with m and R absent; but such an interpretation would rest 

 on a false conception, as I take it, of Mendelian factors; for, the 

 absence of R and of M does not mean that all factors for wings are 

 lost — there may be hundreds of factors that enter into the produc- 

 tion of wingsi) — but only that when a certain factor, R, is lost 

 from the complex, a miniature wing is produced by the remainder; 

 and when the factor M is lost from the complex of wing-factors, a 

 rudimentary wing is produced by the remainder. When both R and M 

 are absent the remaining factors are still capable of forming as much 

 of the wing as is shown by the rudimentary-miniature wing. In fact, 

 this last type of wing bears the same relation to miniature wing that 

 ordinary rudimentary bears to long wing. 



The appearance of this wing makes it possible to carry out a 

 new series of crosses which not only reveal the character of the 

 rudimentary-miniature wing, but serve to test the validity of the 

 system employed to express the relation of the factors to each 

 other. One difficulty has arisen in making the combinations, viz., 

 that of distinguishing in the females the rudimentary from the rudi- 

 mentary-miniature wings. In the males this difficulty is present to 



') At present we know of at least seven other factors affecting the wings of 

 Drosophila, eacli a different loss from the complex of wing factors. 



