308 MUTATION AND PLANT BREEDING 



A. It assumes that genes with strong potentials: 



— exist in the population under study 



— are not showing their maximum expression due to specific buffers 

 - are maintained in a buffered condition in High x High or Low X 



Low crosses (such crosses give some transgressive segregation) 



— segregate free of their specific buffers as a result of High x Low 

 crosses (such crosses give strong transgressive segregation) 



— receive an enhancing effect from specific buffers of the other 

 extreme 



B. It consists of: 



— crossing the best parent with the worst parent for the character 

 under study (High X Low) 



— growing large F 2 populations from such crosses 



— selecting at both ends of the curve for plants showing extreme 

 transgressions (H' and L'); H' is H minus its buffers, and L' is 

 L minus its buffers 



— intercrossing favorable segregates (H' X H', or L' x L') to accu- 

 mulate genes affecting same character or complementary char- 

 acters 



— crossing H' with L and selecting in F 2 for H" (H" = H' plus 

 enhancers from L) 



— crossing L' with H and selecting in F 2 for L" (L" = L' plus 

 enhancers from H) 



— crossing H" X H" and L" X L" for further advance in respective 

 directions 



C. It works as demonstrated by results of sesame breeding programs 

 involving the following characters: 



— length of pods 



— gland number 



— disease resistance (Alternaria and Cercospora) 



— insect resistance (aphids) 



— number of branches 



— dehiscence 



