The Behavior of the Chromosomes as Studied through Linkage. 



237 



This system of nomenclature requires cbanprino; all the symbols used in 

 my former paper. In order to avoid confusion I shall give a list of 

 equivalents. 



Wliite was treated as a double recessive (co), eosin as a single 

 recessive (Co), and the normal red as CO, in the earlier paper. I have 

 given elsewhere (Sturtevant '13bi my reasons for preferring to con- 

 sider this a case of triple allelomorpliism. 



The genes named above were the only ones treated before. They 

 were shown to fall into a linear series, in the relative positions given 

 in the list above: except that W, w, and w« all occupy the same locus, 

 only one of them occurring in any one chromosome. The only possible 

 combination involving two pairs of these genes which was not then con- 

 sidered was that of M and R. Morgax ('12b) has now published ex- 

 tensive data for this cross and for the combination WMR. Safir ('13) 

 has reported the occurrence of a new eye color, called cherry, the gene 

 for which seems best considered as another modification of W. I shall 

 designate this fourth allelomorph as W^. 



Mrs. TiCE ('14) has reported a dominant sex-linked mutation in 

 the shape of the eyes, called barred, and has worked out its approximate 

 position in the X chromosome as being a little beyond R. The normal 

 form of this gene is designated by br', its mutated form by Br'. The locus 

 in the chromosome I shall refer to as Br. Morgan ('12 c) has also re- 

 ported a sex-linked "lethal" factor, lying near W. This is not a a very con- 

 venient mutant to work with when, as in the present case, the main object 

 is to secure as many accurate data on linkage as possible; moreover, its 

 position is so near to W and Y that it does not give results which are 

 likely to bring out any relations not more easily obtainable by using 

 one of these loci. For this reason I shall not consider the gene in this 

 paper, except to state that Morgan's data indicate that it lies about 

 0-4 units from W: the data involving lethal and M corroborate this, 



