sj GENETICS IN RELATION TO AGRICULTURE 



constitution is WwSs, and it contains two pairs of factor contrasts. 

 Such a hybrid produces gametes representing all possible combinations 

 containing one member of each pair of factors. The gametes, therefore, 

 will be produced in the combinations and proportions 



1 WS:1 Ws:l wS:l ws. 



This series of gametes will be represented in both the pollen grains and 

 ovules, so that if each kind of ovule has an equal chance of being fertil- 

 ized by any one of the four kinds of pollen grains the following combina- 

 tions will result. 



TABLE X. COMBINATIONS OF FACTORS AND CHARACTERS RESULTING FROM 



SELF-FERTILIZATION OF A PURPLE STARCHY CORN OF THE 



COMPOSITION WwSs. 



WS ovule and WS pollen grain gives WWSS, purple starchy 



WS ovule and Ws pollen grain gives WWSs, purple starchy 



WS ovule and wS pollen grain gives WwSS, purple starchy 



WS ovule and ws pollen grain gives TFwSs. purple starchy 



W* ovule and WS pollen grain gives WWSs, purple starchy 



Ws ovule and Ws pollen grain gives JTWss, purple sweet 



Ws ovule and wS pollen grain gives WwSs, purple starchy 



Ws ovule and ws pollen grain gives Wwss, purple sweet 



wS ovule and WS pollen grain gives WwSS, purple starchy 



wS ovule and Ws pollen grain gives WwSs, purple starchy 



wS ovule and wS pollen grain gives wwSS, white starchy 



wS ovule and ws pollen grain gives wwSs, white starchy 



tea ovule and WS pollen grain gives WwSs, purple starchy 



ws ovule and Ws pollen grain gives Wwss, purple sweet 



ws ovule and wS pollen grain gives wwSs, white starchy 



ws ovule and ws pollen grain gives wwss, white sweet 



When the FZ grains are classified according to their phenotype, 

 they are distributed as follows: 



9 grains with purple aleurone and starchy endosperm 

 3 grains with purple aleurone and sweet endosperm 

 3 grains with white aleurone and starchy endosperm 

 1 grain with white aleurone and sweet endosperm 



Just as the 3 : 1 ratio is typical for the monohybrid when one of the 

 contrasted characters is dominant, so the 9:3:3:1 ratio is charac- 

 teristic of dihybrids when one member of each pair of characters is domi- 

 nant. This ratio is clearly derivable from the simple 3:1 ratio, for 

 considering first aleurone color, the segregation is in the ratio 3 purple:! 



