NEW DATA. 



49 



and are recorded in table 24. The four classes of females were not 

 separated from each other, but the total of females is given in the table. 



Table 24. — Pi lemon (ket.) 9 X cherry vermilion cfcf. Fi wild-type 9 X 



cherry vermilion d' c? . 



There are three loci involved in this cross, namely, cherry, lemon, and 

 vermilion. Of these loci two were known, cherry and vermilion. The 

 data are consistent with the assumption that the lemon locus is between 

 cherry and vermilion, for the double cross-over classes (the smallest 

 classes) are cherry lemon vermilion and wild type. The number of 

 single cross-overs between cherry and lemon and between lemon and 

 vermilion are also consistent with this assumption. Since lemon flies 

 fail to emerge successfully, depending in part upon the condition of the 

 bottle, the classes involving lemon are worthless in calculating crossing- 

 over and are here ignored. In other words, lemon may be treated as 

 though it did not appear at all, i. e., as a lethal. The not-lemon 

 classes — cherry, vermilion, cherry vermilion, and wild type — give the 

 following approximate cross-over values for the three loci involved: 

 Cherry lemon, 15; lemon vermilion, 12; cherry vermilion, 27. The 

 locus of lemon, calculated by interpolation, is at about 17.5 



LETHAL 2. 



In September 191 2 a certain wild female produced 78 daughters and 

 only 16 sons (Morgan, 1914^); 63 of these daughters were tested and 

 31 of them gave 2 females to i male, while 32 of them gave i : i 

 sex-ratios. This shows that the mother of the original high sex-ratio 

 was heterozygous for a recessive sex-linked lethal. In order to deter- 

 mine the position of this lethal, a lethal-bearing female was bred to an 

 eosin (or white) miniature male, and those daughters that were hetero- 

 zygous for eosin, lethal, and miniature were then back-crossed to 



