614 



THE AMEBIC AN NATURALIST [Vol. XLVr 



If the numbers obtained in F 2 of the cross of Tom 

 Thumb pop with California pop are to be regarded as 

 constituting a tetrahybrid ratio, all four aleurone factors 

 must be heterozygous in ¥ 1 the formula being CcRrPpIi. 

 The F 2 generation would then be constituted as follows t 



27 CRPi 27 purple 



9 CRpi 9 red 



9 CrPi 



9 cRPi 



3 Crpi 



3 cRpi 



3 crPi 



1 crpi 

 81 CRPI 

 27 CRpi 

 27 CrPI 

 27 cRPI 



9 Crpi 



9 cRpi 



9 crPI 



3 crpi j 



If either C or R is homozygous in F 1? the resulting F 2 

 ratio should approximate 9 purple : 3 red : 52 white. 



The actual numbers fell between these two theoretical 

 ratios, as is seen from the following comparison : 



From the ratio alone it is plainly impossible to say 

 whether the cross in question is a tetrahybrid or a tri- 

 hybrid. Of course behavior of the reds and purples in F 3 

 will settle the matter. If, for instance, either C or R is 

 homozygous, one third of the F 2 red grains should breed 

 true and two thirds produce reds and whites in the ratio 

 of 3: 1, while if both are heterozygous, only one ninth of 



