648 VERMILION-DEFICIENCY 



sable-duplication, garnet, and forked in the other X ( — - ). 



The progeny (Table II) agreed with the expectation except that in 

 addition to these genes of the mother a new lethal had appeared which 

 killed off half the males. The lethal gene had appeared by muta- 

 tion in the S g / X derived from the father, and its locus was 20 or 

 more units from forked on the basis of the eleven crossovers in a 

 total of 55 sons. This distance is great enough so that it was thought 

 probable that the locus of the lethal was to the left of forked rather 

 than further toward the distal end of the chromosome. No great 

 importance was attached to this occurrence of a lethal, since they 

 occur frequently; no less than five were detected in the early work on 

 sable-duplication . 



In the next generation a start was made to determine the locus of 

 tiny-bristles, the slight information already in hand having indicated a 

 position some 6 or 8 units to the left of sable; that is, in the neigh- 

 borhood of miniature. It was thought more advisable to use ver- 

 milion before miniature, since there was some chance that the small 

 size of the wings of the tiny-bristle mutation would interfere with the 

 classification of the miniature wing character. Accordingly, some of 

 the garnet daughters of Culture 3,680 were outcrossed to vermilion 

 forked males. Eight of these daughters gave progeny in accordance 



with the constitution ( ^-^ ) (Table III) which furnished data 



\S s g / 



with respect to the amount of crossing over between tiny-bristle and 

 forked. 



However, two daughters (Table IV) gave results different in two 

 respects: the lethal found present in the parental culture was here 

 evidenced in the fact that there were only half as many males as 

 females (866^: 181 9), and in the fact that the locus of this lethal 

 corresponded to the position calculated for the lethal present in the 

 previous generation, since its location was 19 units to the left of forked 

 and about 2 units to the left of tiny-bristles. The mothers of the 

 two cultures had come from eggs representing normal crossing over 

 between the lethal and sable in Female 3,680. All the above results 

 are normal; however, a totally unexpected feature appeared in the 



