114 The Nature of Biological Diversity 



The members of each group are distinguished from the members of 

 the alternate group by a difference in charge, which can plausibly be 

 attributed to the substitution of a single amino acid in the primary 

 protein product of the gene. This product would then be modified 

 into four distinguishable esterases that are inherited as a group. 



In a similar analysis of alkaline phosphatases in Escherichia coli, 

 Bach et al. (1961) found five electrophoretically distinguishable forms 



( + ) 



(-) 



ORIGIN 



FIG. 10. Zymogram of esterases in Drosophila. Homogenates for each insertion 

 were made from five adult male flies less than 24 hours old. Electrophoresis through 

 the starch gel occurred for 6 hours at a voltage drop of 4 v/cm and a pH of 8.7. 

 Starch was made up in Tris huffer, 0.5 M. Alpha-naphthyl acetate was used as sub- 

 strate and fast blue BB as dye coupler. Drosophila strain Am is highly inbred and 

 shows an esterase at position 5 but not at position 4. Strain CH is not homozygous 

 but contains flies with esterases at positions 4 or 5 or both. When a strain CH fly 

 (with an esterase at position 4 but not 5) is crossed to strain Am, the Fi offspring 

 all show esterases at both positions. 



