82 



The Journal of Heredity 



I 



I 



I 



CROWN AND EDGE VIEWS OF NORMAL AND ABNORMAL KERNELS 



The first two rows at the left show kernels in which the enfiosperni is completely developed. 

 Those in the third row are cut in cross-section to show the cavities which are often found in the 

 upper part of shrunken kernels. The 4th, 5th and 6th rows show the variation in the size and 

 shape of shrunken kernels. In the last row at the right the kernels are cut to expose the cavities 

 in the upper part of the endosperm. (Fig. 24.) 



plant of the genetic constitution 



c sh 



C Sh 



by the double recessive 



c sh 



c sh 

 Again it 



will be noted that while most of the 

 colored kernels are smooth and most 

 of the colorless ones shrunken a few 

 kernels show the opposite combina- 

 tions of these characters. 



To determine the linkage relation 

 of shrunken and waxy a non-shrunken 

 waxy plant of the genetic constitution 

 Sh Sh 1VX wx was crossed with a 

 shrunken starchy plant of the constitu- 

 tion sh sh Wx Wx. Several F, plants of 

 this cross were backcrossed to double 

 recessive shrunken waxy jjlants. Twelve 

 ears were obtained from these pollina- 

 tions containing a total of 2,105 kernels 

 which were distributed amf)nK llic four 

 possible classes as follows: 



Here the parental combinations of the 

 two factor pairs concerned total 1,646 

 and the new combinations 459. The 

 crossover percentage for Sh sh and Wx 

 wx in these particular crosses is 21 . 8. 



On the basis of these data the 

 probable order of the three genes in this 

 linkage group is 



C Sh Wx 



sh 

 3.4 



wx 



25.2 



It must be remembered, however, 

 that the percentage of crossing-over is 

 variable and that the order of the genes 

 can clefinitely be detennined only in 

 backcrosses where all three pairs of 

 factors are involved at once. Material 



