Inheritance in the Higher Plants 



95 



bb-\-2AaBB-\-4AaBb. Since heterozygotes resemble homo- 

 zygotes in appearance in the cases of complete dominance, 

 however, the visible appearance of the F^ generation is 

 gAB : ^Ab : 3a5 : lab. 



Perhaps the easiest method of showing the combinations 

 of gametes in Mendelian inheritance is by the use of four 

 squares multiplied once by four for each character pair. 

 In the case of dihybrids sixteen squares are necessary. 

 Write each possible gametic combination of the male cells 

 in each horizontal row of squares, AB, Ab, aB, and ab. 

 Next write the same combinations for the female gametes 

 in each vertical column of squares. This gives all the 

 zygotic combinations possible. 



We are now ready to see just why one cannot tell whether 

 he is dealing with a simple or complex state of affairs in 

 Mendelian inheritance. In the monohybrid ratio of purple 

 and non-purple aleurone cells of maize the segregation in the 

 F2 generation is: 



P p 



P P 



P p 



P P 



Three purples to one non-purple are produced. 



In the dihybrid ratio when other white varieties were 

 used as one of the parents, nine purples to seven non-purples 

 were produced. This simply means that two factors are 

 necessary to produce the pur[:)le color. These factors may 



