2O2 T. H. MORGAN. 



the offspring are normal. When an FI male was mated to 

 dachs black females the following results were obtained : 



Normal Gray. Dachs Gray. Normal Black. Dachs Black. 



98 O o 72 



These results are consistent with the hypothesis of no crossing 

 over in the male. Since dachs lies on the other side of black 

 from purple and vestigial, the data extend the application to 

 a new section of the second chromosome, and considerably 

 increase the significance of the results. 



Another recessive mutant stock has wings curved in an arc. 

 "Arc" was combined with black both belonging to the second 

 group of factors. When black arc was mated to wild flies (with 

 straight wing) the offspring were normal. An FI male back 

 crossed to black arc gave the following results: 



Gray Straight. Black Straight. Gray Arc. Black Arc. 



1 6 1 O O 145 



This result also is conformable with the hypothesis of no crossing 

 over in the male, and since arc lies on the same side of black as 

 does purple and vestigial but considerably beyond either, still 

 a new section is found to be free from, crossing over in the male. 

 Further, since in the female there is a very great amount of 

 crossing over (about 36 per cent.) between black and arc, the 

 lack of crossing over in the male is even more striking. 



W 7 hen black was crossed to purple the FI flies were gray red. 

 An FI male was mated to a black purple female and gave in the 

 next generation : 



Gray Red. Black Red. Gray Purple. Black Purple. 



O 74 .71 O 



These results are again conformable with the hypothesis. In 

 this case the two recessives entered from different sides. 



Another mutant caaracter, streak, is a dominant. Streak 

 gray mated to normal (thorax) black gave streak gray FI flies. 

 An FI male was mated to the double recessive, normal black 

 females, and gave the following classes: 



Streak Gray. Normal Gray. Streak Black. Normal Black. 



19 O 21 



