244 



EVOLUTION, GENETICS, AND EUGENICS 



hybrid progeny would all be tall, smooth, yellow, since these three 

 characters are dominant. Inbreeding the hybrids gives the following 

 result in the F 2 generation: 27 tall smooth yellow, 9 tall smooth green, 



Gametes 



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Fig. 57. Diagram illustrating dihyb rid ratio. Upper part shows how original 

 parents were crossed to give F z hybrid; lower part shows F r hybrid producing 

 four kinds of gametes; chance matings among these gametes, when F t is inbred, 

 result as indicated in the large set of squares and explains the 9:3:3:1 ratio in 

 the F 2 generation. (From Coulter and Coulter.) 



9 tall wrinkled yellow, 9 dwarf smooth yellow, 3 tall wrinkled green, 

 3 dwarf smooth green, 3 dwarf wrinkled yellow, 1 dwarf wrinkled 

 green. The trihybrid ratio therefore is 27:9:9:9:3:3:3:1. This 

 involves 64 individuals and 8 phenotypes. 



