158 



CREIGHTON AND MCCLINTOCK 



Table 1 



Knob-interchanged Knobless-normal, culture 337 and 



Knobless-normal 



Knobbed-normal cultures A125 and 340 



plants heterozygous for the knob and 

 possessing two normal chromosomes. 

 The functioning of gametes which 

 had been produced as the result of 

 crossing-over between the knob and 

 the interchange would give rise to ( 1 ) 

 individuals heterozygous for the knob 

 and possessing the interchanged chro- 

 mosome and (2) those homozygous 

 for the knob and possessing two nor- 

 mal chromosomes. The results of such 

 crosses are given in culture A125 and 

 340, table 1. Although the data are 

 few, they are consistent. The amount 

 of crossing-over between the knob 

 and the interchange, as measured from 

 these data, is approximately 39%. 



In the preceding paper it was shown 

 that the knobbed chromosome carries 

 the genes for colored aleurone (C), 

 shrunken endosperm (sh) and waxy 

 endosperm (wx). Furthermore, it was 

 shown that the order of these genes, 

 beginning at the interchange point is 

 wx-sh-c. It is possible, also, that these 

 genes all lie in the short arm of the 



knobbed chromosome. Therefore, a 

 linkage between the knob and these 

 genes is to be expected. 



One chromosome number 9 in a 

 plant possessing the normal comple- 

 ment had a knob and carried the genes 

 C and wx. Its homologue was knobless 

 and carried the genes c and Wx. The 

 non-crossover gametes should contain 

 a knobbed-C-irx or a knobless-c-TFx 

 chromosome. Crossing-over in region 1 

 (between the knob and C) would give 

 rise to knobless-C-i:;;!: and knobbed- 

 c-lVx chromosomes. Crossing-over in 

 region 2 (between C and ivx) would 

 give rise to knobbed-C-TF^f and knob- 

 less-^-u'jir chromosomes. The results 

 of crossing such a plant to a knob- 

 less-c-ii'x type are given in table 2. 

 It should be expected on the basis 

 of interference that the knob and C 

 would remain together when a cross- 

 over occurred between C and wx; 

 hence, the individuals arising from 

 colored starchy (C-Wx) kernels 

 should possess a knob, whereas those 



Table 2 



Knob-C-Tua: 

 Knobless-r-M^A: 



X Knobless-c-TTX 



