SUMMARYFour characters, ADH activity at 25°, immunologically determined ADH protein level, total protein and body weight were measured upon 72 hour old adult female and male Drosophila nelanogaster from 16 highly inbred lines, derived from the laboratory population, Texas" (established 1966). The highest levels of ADH activity and ADH protein level were observed in the 2 lines homozygous for the AdhF allele. Amongst the 14 Adh lines variation for ADH protein level was associated with genetical variation for ADH activity (P = 0.6). The genetical association between ADH activity or ADH protein level and either body weight or total protein in the 16 inbred lines was not statistically significant. A study of ADH activity, ADH protein and total protein in 8 lines representing all homozygous combinations of chromosomes I, II and III and derived from two inbred Adh lines, chosen for their respective high and low ADH activities, showed that ADH activity was considerably modified by a post-translational event controlled from chromosome III. Total protein was controlled by different chromosomal effects from those controlling ADH activity. Michaelis constants for crude fly extracts of the two AdhFP and the above two Adh S/S lines showed clear differences in affinity for isopropanol.

A method is described for assessing the non-randomness of protein compositions, based on the chi-squared statistic for the differences between the observed numbers of residues of each type and the numbers expected for a random distribution of codons. The analysis indicates that changes in at least 30% of the residues in natural proteins are selected against.

SUMMARYGenotype-environment interaction was detected for ADH activity amongst a set of 18 highly inbred lines of Drosophila melanogasler which had been extracted from the laboratory p.ppulation, "Texas". The genotype-environment interaction for ADH activity was not wholly associated with genotype-environment interaction for body weight or total protein level. Detailed analyses of the responses of the individual inbred lines in ADH activity in relation to the environmental index, e1 and following the procedure of Jinks and Pooni (1979), showed substantial diversity in the form of response. Lines homozygous for the AdhF allele were more environmentally sensitive than Adh lines. Amongst the 16 Adh lines, models of linear, quadratic or two intersecting-straight-lines were used to illustrate the varied responses of genotypes to the environment. The heterogeneity in the response characteristics of the inbred lines was attributed to variations in the conditions of culture media normally present within populations and laboratories. Moreover the non-linear responses shown by some lines to the environment are Consistent with a model of genotype-environment interaction for ADH activity mediated by varied genotype-specific sensitivities to different environmental factors.

SUMMARYFifteen highly inbred lines extracted by sib-mating from the laboratory cage population, "Texas ", of Drosophila melanogaster were crossed in a half-diallel mating design. Female progeny were assayed individually for ADH activity at 25° and 35°C and for total protein. At 25°C there was considerable additive genetical variation and the dominance variation was attributable to specific parents and to specific crosses at random in the diallel table. The character total protein also showed considerable additive variation but less dominance variation. Largely independent gene action was shown by the characters ADH activity and total protein. There were strong genotype-environment interactions for heat-stability. At 35°C most of the genetical variation was additive and mainly due to modifier loci. It was concluded that at 25°C dominance was ambidirectional and almost complete. This genetical architecture was compatible with a past history of stabilising selection for ADH activity in the "Texas " population.