180 GENETICS 



coveries while breeding wheats at the Agricultural 

 Experiment Station of Svalof in Sweden. 



8. THE NILSSON-EHLE DISCOVERY 



Nilsson-Ehle, 1907, found in breeding together 

 different strains of wheat that a certain wheat with 

 brown chaff crossed with a white-chaffed strain yielded 

 only brown-chaffed wheat in the first generation. 

 These heterozygous or hybrid brown-chaffed wheats 

 when crossed with each other produced, not the ex- 

 pected proportion of three brown to one white, but 

 fifteen brown to one white. This was not explainable 

 as the chance result of a single cross, but was the con- 

 clusion drawn from fifteen different crosses, all of the 

 same strains, that yielded a total progeny of 1410 

 brown-chaffed to 94 white-chaffed plants, which hap- 

 pens to be exactly the proportion of fifteen to one. 



In other experiments it was discovered that although 

 dominant red-kerneled strains of wheat crossed with 

 white-kerneled varieties usually gave the three-to-one 

 proportion upon segregation in the second filial genera- 

 tion, yet one particular strain of red-kerneled Swedish 

 wheat in the second generation gave approximately 

 sixty-three red to one white-kerneled strain. 



The explanation of these two unexpected results is 

 this. In the case of brown-chaffed wheat there are two 

 independent determiners for the character of brown 

 color, and these simply follow the Mendelian laws for 

 a dihybrid, while in the case of the red-kerneled -wheat 

 there are three independent determiners for the charac- 



