Aktaltsis of Heteeogeneity in Complex Chaeactees 



265 



of 1:2:1. Within each of these groups, however, the pronotal pattern shows 

 considerable diversity. 



The least numerous groups are those with the narrow form of multilineata, 

 and here two types of pronotal pattern occur in about equal frequency — a com- 

 pletely black one and one or more of the biotypes in the 9, 10, 11, and 12 groups. 



Fig. 48.- 



Biotype 1 Biotype 12 



+ + 



^multitaeniata form multilineata form 



-Graphic representation of the action of the form-determiner In the 

 alteration of the color pattern of the pronotum. 



The second class shows wholly black, while the most common group shows black 

 and a variable array of pattern, as shown in figure 48. In the least numerous 

 group are found blacks that are both homozygous and heterozygous, and from 

 these it is a simple matter to extract a homozygous-acting strain that has the 

 melanothorax pronotal pattern in combination with the determiner for multi- 

 lineata, a narrow elongated type. Two test agents, races, are now available, each 

 with the same pronotal complex but associated with the two different form-deter- 

 miners, and each in pure homozygous-acting biotypes. 

 18 



