THE MUTATED GENE 



141 



discussed above, that the action of these "alleles" consists in 

 destroying; facet-forming material during development (parallel 

 to the destruction of wing material in the vestigial case), we may 

 express the actual facet numbers as percentages of the number 

 in the Wild type and represent the action of the genes as the per- 

 centage destruction of facets. This is done in the first group of 

 Table 16, and Fig. 28 gives the curve obtained from these data 

 (the crosses are values of this series). From the curve we may 



100 

 90 

 80 



5 70 



xB series 

 o Bi series 

 o Combination 

 series 



3 4 S 



Doses 



Fig. 28. — Curve plotted for the Bar and Infrabar series. Plotting actual and 

 interpolated doses against percentage destruction of facets. 



now calculate the eventual dosage of Infrabar. If this allele also 

 represents a dosage difference from the Wild-chromosome 

 section, it must be a dose between one and two. If we designate 

 as X the difference between the Bar duplication (2B + ) and the 

 Infrabar of smaller dosage (between 1 and 2B + ), the Infrabar locus 

 contains the dosage 2B+ — X, or one dose B + and one B+ — X. 

 The different combinations of B + and B l contain then different 

 doses of B + — X, as tabulated in the second section of the table 

 (second and third columns). To prove that B l is a dosage 

 difference, viz., 2B + — X, we mark the percentage loss of facets 

 in the B' combinations on the curve obtained for B (the points O 

 in the seriation of the table). The corresponding points on the 

 abscissa (dotted lines) tell us which dosage of B + = 1 would have 

 been needed to produce this effect in the Bar series, which fur- 



