34 LEONELL C. STRONG. 



fly other than one that was also roughoid. However, their 

 occurrence is very inconstant, most roughoid eyes being as light 

 red as the normal wild type. 



CHROMOSOME CARRYING ROUGHOID. 



The first experiment (culture No. 142) consisted in out- 

 crossing a roughoid male to a female showing the second-chromo- 

 some recessive vestigial. 1 The FI generation flies were all wild 

 type, thus proving roughoid to be a recessive character. By 

 inbreeding the FI flies, F? was obtained. One quarter of the F2 

 vestigials showed the roughoid character (culture No. 1426). 

 The presence in F 2 of the double recessive class proves that 

 roughoid cannot be located in the second chromosome. At the 

 same time, I out-crossed a roughoid female to a dichaete hairless 

 male from stock (culture No. 141). These two characters are 

 thirdrchromosome dominants. By back-crossing the FI dichaete 

 hairless females to roughoid males from stock, evidence was ob- 

 tained that roughoid shows linkage relations with these mutants 

 in the third chromosome. The size relation of the various classes 

 indicated that roughoid was considerably to the left of dichaete. 

 As the back-cross flies were not hatching out as well as expected, 

 I did not complete the count of the cultures of this experiment. 



A cross between roughoid and the original rough gave in FI 

 only wild-type flies, showing that roughoid was neither rough nor 

 an allelomorph of rough. 



LOCATION OF ROUGHOID IN THE THIRD CHROMOSOME. 

 The next step was to make up a stock containing both the new 

 character, roughoid, and sepia (located at the extreme left end of 

 the then known third chromosome). In the third generation 

 from a cross between roughoid and sepia, I obtained such a stock. 

 Since I had obtained roughoid and sepia together in such a short 

 time, I concluded that the two were not very closely linked. 

 By using the back-cross method, I obtained the following results: 



1 This female was from the stock known as "5 pie" and carried in addition to 

 vestigial, the second-chromosome recessives black, purple, arc and speck. These 

 other characters were disregarded in the Fs classifications. 



