1. Location of Dt in the short arm of chromosome 9. F2 data presented in the 1941 News Letter indicate that Dt is situated close to the yg2 locus at the end of the short arm of chromosome 9. These data also suggested that Dt was about ten units beyond yg2. However, Creighton found only one percent recombination between yg2 and the terminal knob. Backcross tests recently completed prove that Dt does lie approximately seven units beyond yg2. The low recombination value of one percent for the yg2-knob region may be ascribed to the disturbing effect on crossing over of the large heterozygous knob present in Creighton's set-up. The backcross data are as follows:

Dt +  +  +
+ yg2 sh wx

 

0 1 2 3 1-2 2-3 1-3 Total
 
333 278 22 23 76 86 82 64 0 3 2 3 0 0  
611 45 162 146 3 5 0 972
 
Dt-yg2 5.2% Yg-Sh 17.4% Sh-Wx 15.8%  

 

Dt +  +
 + yg2 sh

 

0 1 2 1-2 Total
 
306 228 18 33 83 93 2  4  
534 51 176 6 767
 
Dt-yg2 7.4% yg2-Sh 23.7%  

 

  Dt+ Dt yg2 ++ +yg2 Total
Dt   + 283 24 25 293 625
+  yg2

Dt-Yg2 7.8%

 

Dt  +  +
+  sh wx

 

0 1 2 1-2 Total
 
345 330 115 110 85 76 3 4  
675 225 161 7 1068
     
Dt-Sh 21.7% Sh-Wx 15.7%  

 

  Dt+ Dt sh ++ +sh Total
Dt   +  
+   sh 838 277 324 765 2204

Dt  Sh 27.3%