OF MUTANT CHARACTERS. 



287 



curved were classified and no attention was paid to black. The result 

 was rather unexpected, for while crimson and curved jiroved to l^e 

 independent (56 per cent recombinations), the curved flies constituted 

 only 31.4 per cent of the flies instead of 50.0 per cent (table 131). Thb^ 

 difference was not clearly recognized until the counts were totaled, 



Table 131. — Pi, dimson black curved d^ X xvild 9 ; B. C, Fi wild- 

 type 9 + crimson black curved father. 



and there were then no more flies hatching. However, one of these Fj 

 cultures was recovered from the discards and a count was taken of it. 

 This count showed no black curved flies whatever, and far too few blacks 

 and curved. The case of dachs-lethal was then being followed, so that 

 a hypothesis was known that covered this situation. It was concluded 

 that an autosomal lethal had arisen by mutation in this second chro- 

 mosome at a locus between black and curved. No black curved flies 



Table 132. — Offspring given by pairs of wild-type flies from an Fz (Fj) parallel 



to the back-cross of table 131. 



appeared in the F2, because eveiy black curved zygote (except the 

 rare double cross-over) was at the same time homozygous for the lethal. 



6 l ++\ 



a '''++ 



By crossing-over between black and the lethal ( -, — ; — - — > 



few black flies would be produced (-—- — ); likewise the few curved 



\o I c / 



flies corresponded to crossing-over between the lethal and curved. 

 If this were the explanation, then most of the wild-tyi)e fli(>s should 



be of the same constitution as the Fi flies ( ^ j and wIkmi mated 



together should repeat the F2 result. \+ + -|- 



