THE MUTATED GENE 171 



On page 96, we mentioned the fact that anthocyanin may be 

 cyanin or pelargonidin. But in Dahlia, A and B do not control 

 one or the other; rather the whole quantitative system of the 

 genes involved determines this alternative. Pelargonin pro- 

 duction, for example, depends upon the following factorial 

 proportions : 



1. A or B together with Y. 



2. Two or more B. 



3. One or more B together with three I. 



4. One or more B together with two or more I and at least 

 one A. 



5. One or more B together with one I and at least three A. 

 The whole body of these facts is summed up in a quantitative 



representation based upon the arbitrary assumption that the 

 limit of pigment source that can be made available in Dahlia, 

 whatever factors are present, can be expressed as six units. The 

 potential units of the different genes are then calculated in the 

 following way : B and Y are capable of using the maximum source 

 in simplex condition and therefore contribute at least six potential 

 units. A has a cumulative potential value which in quadriplex 

 condition is less than or equal to the maximal source. Following 

 this way of estimation, unit values fitting the facts are fixed as 

 Y = 9, B = 6, 1=1, A = 1/2, and their combined action 

 would be, in a few examples, if 8 is the threshold value for 

 pelargonidin : 



Only cyanin 



AJt = 6 units) 



BiAJi = 8 units \ 



A\Y\ = 9.5 units) 



BiAJ 2 = 8.5 units > Only pelargonin 



Bo = 12 units ) 



Thus the entire body of evidence leads to the following con- 

 clusions : 



1. The potential unit values of the four color factors are as 

 given above. 



2. A sum total of six units is sufficient to produce the maximum 

 pigment source that plants carrying B or Y are capable of 

 supplying. In /U-plants, this maximum is two units. 



3. Each dominant factor may contribute to this source accord- 

 ing to its potential unit value. But the actual units are limited 

 to 6 (or 2) whatever the potential units. 



