322 



Interaction of Genes 



In these plants, genes w and Y interact to give yellow and 

 w and y interact to produce green, but W interacts with both Y 

 and y to produce the same character, white. A testcross of the 

 heterozygote to a green plant would result in a ratio of 2 white 

 (IWY + IWy) : 1 yellow (wY) : 1 green (wy). 



TABLE 17 



Fi AND F2 FROM Various Combinations of Crosses among Rough-, Smooth-, 

 Near-Smooth, and Intermediate-Awned Types of Durum Wheat 



(From work of Knowles in the Canadian Journal of Research.) 



Knowles has reported a study in wheat in which the hypostatic 

 genes showed incomplete dominance. In durum wheat, gene R 

 produces rough awns, whereas its recessive produces awns that 

 are not rough. Another pair of genes, S and s, also affects the 

 awns. If a plant is rr &&, it has awns intermediate between 

 smooth and rough; if it is rr Ss, the awns are nearly smooth; in 

 rrss plants the awns are smooth. Various crosses produce the 

 results listed in Table 17. 



