46 A. H. STURTEVANT 



O. Flies recessive with respect to 0(o) have eosin eyes. The 

 relation between C and O has been explained by Morgan in a 

 paper now in print and about to appear in the Proceedings of the 

 Academy of Natural Sciences in Philadelphia. 



P. Flies with p have vermilion eyes instead of the ordinary 

 red (Morgan '11 d). 



R. This and the next factor both affect the wings. The nor- 

 mal wing is RM. The rM wing is known as miniature, the Rm 

 as rudimentary, and the rm as rudimentary-miniature. This 

 factor R is the one designated L by Morgan ('11 d) and Morgan 

 and Cattell ('12). The L of Morgan's ^rlier paper ('11) was 

 the next factor. 



M. This has been discussed above, under R. The miniature 



and rudimentary wings are described by Morgan ('11 a). 



C 

 The relative position of these factors is B, — , P, R, M. C and 



O are placed at the same point because they are completely linked. 

 Thousands of flies had been raised from the cross CO (red) by 

 CO (white) before it was known that there were two factors 

 concerned. The discovery was finally made because of a mutation 

 and not through any crossing over. It is obvious, then, that 

 unless coupling strength be variable, the same gametic ratio must 

 be obtained whether, in connection with other allelomorphic 

 pairs, one uses CO (red) as against co (white), Co (eosin) against 

 CO (white), or CO (red) against Co (eosin) (the cO combination 

 is not known). 



METHOD OF CALCULATING STRENGTH OF ASSOCIATION 



In order to illustrate the method used for calculating the 

 gametic ratio I shall use the factors P and M. The cross used 

 in this case was, long winged, vermilion-eyed female by rudiment- 

 ary winged, red-eyed male. The analysis and results are seen 

 in table 1. 



It is of course obvious from the figures that there is something 

 peculiar about the rudimentary winged flies, since they appear 

 in far too small numbers. This point need not detain us here, 

 as it always comes up in connection with rudimentary crosses. 



