186 GENETICS 



discoveries while breeding wheats at the Agricultural 

 Experiment Station of Svalof in Sweden. 



i 

 8. THE NILSSON-EHLE DISCOVERY 



Nilsson-Ehle 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 expected 

 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 conclusion 

 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 happens 

 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 generation, 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 deter- 



