64 



SEX-LINKED INHERITANCE IN DROSOPHILA. 



LINKAGE OF SHIFTED, VERMILION, AND BAR. 



In order to determine on which side of vermiHon shifted lies, a shifted 

 vermiHon (not-bar) female was crossed to a (not-shifted red) bar male. 

 Three factors are involved, of which one, bar, is dominant. The 

 shifted vermilion (not-bar) stock is a triple recessive, and a three-point 

 back-cross was therefore possible. The daughters were bar and the 

 sons were shifted vermiHon (the triple recessive). Inbred these gave 

 the results shown in table 46. The smallest classes (double cross-overs) 

 are shifted and vermilion bar, which places shifted to the left of ver- 

 miHon at approximately 17.8 units from yellow. 



Table 47. — Pi shifted vermilion 9 X bar d^cT. F\ bar 9 X Fi shifted 



vermilion cf cf • 



The stock of shifted has been thrown away, since too great difficulty 

 was encountered in maintaining it, because, apparently, of sterility in 

 the females. 



LETHALS SA AND SB. 



The first lethal found by Miss Rawls was in a stock that had been 

 bred for about 3 years. While there was no a priori reason that could 

 be given to support the view that lethal mutations would occur more 

 frequently among flies inbred in confinement, nevertheless a hundred 

 females from each of several newly caught and from each of several 

 confined stocks were examined for lethals (Stark, 191 5). No lethals 

 were found among the wild stocks, but 4 were found among the confined 

 stocks. Whether this difi^erence is significant is perhaps open to ques- 

 tion. The first lethal was found in January 1913, in a stock that had 

 been caught at Falmouth, Massachusetts, in 1911, and had been inbred 

 for 18 months, i. ^., for about 50 generations. This lethal, lethal sa, 

 was recessive and behaved like the former lethals, being transmitted 

 by half the females and causing the death of half the sons. The posi- 

 tion of this lethal in the X chromosome was found as follows, by means 

 of the cross-over value white lethal sa. Lethal-bearing females were 

 mated to white males and the lethal-bearing daughters were again 

 mated to white males. The white sons (894) were non-cross-overs and 

 the red sons (256) were cross-overs. The percentage of crossing-over 



