The loci eda, edd and zwf form a tightly linked cluster in E. coli that functions in the metabolism of galacturonate, gluconate and glucose. This cluster has been transferred from six natural isolates into the genetic background of E. coli K12 and examined with regard to effects on growth rate in chemostats. Although the naturally occurring eda and zwf alleles are selectively neutral, the edd alleles are not. The edd alleles fall into three functional classes distinguished by their effects on growth rate in gluconate medium, the most common classes differing in fitness by approximately 1% per hour. This extensive non-neutral genetic variation of edd is discussed in light of the evident rarity of gluconate as a natural substrate. We propose that gluconate selection is intermittent in space or time, providing the population an opportunity to accumulate non-neutral genetic variants during periods of relaxed selection. Such genetic variants will eventually be sorted out by the intermittent periods of gluconate selection, and during these periods the linked eda and zwf alleles will experience pronounced hitchhiking effects.

Two mutations at the niaD locus (structural gene for nitrate reductase apo-protein) are genotypically suppressible. Both mutations result in loss of nitrate reductase enzyme activity and cross reacting material and are non complementing, nonleaky and highly revertible. They have the properties of nonsense mutations. This implies that some of the allele specific suppressors, which act on these and alleles at several other loci, are nonsense suppressors.

I report the results of an experimental study of the effects of sex ratio and density on the mean and variance in offspring numbers in both sexes of the flour beetle, Tribolium castaneum. The variance-effective number is estimated from the observed variance in offspring numbers using the methods of Crow & Morton (1955).

Both the mean and the variance in offspring numbers were found to vary with sex ratio and density; as was found in previous studies (Wade, 1980), males were generally more variable in offspring numbers than females. The ratio of variance to mean progeny numbers in each sex was approximately unity at all sex ratios.

Minute (M) lesions exhibit a striking propensity for interacting with many different mutations. In the past, few attempts have been made to explain these diverse phenomena. This study describes a variety of temperature-sensitive (ts) interactions exhibited by the ts third chromosome Minute mutation M(3)LS4Q-III (Q-III). Most of these interactions (i.e. those involving vg, cp, Dl, Dfd or Ly) reflect Q-III-induced enhancement of the respective mutant phenotypes at the restrictive temperature. However, Q-III also suppresses the extra-sex-comb phenotypes of Pc and Msc at 29 °C and evokes lethal and bristle traits when combined with J34e at the restrictive temperature. All of these interactions are characteristic of non-ts Minute lesions and thus they appear to be correlated with general physiological perturbations associated with the M syndrome. In addition, our findings show that mutations that affect ribosome production and/or function, namely su(f)ts67g and bbts−1, exhibit interactions comparable to those elicited by Q-III. Hence, in accordance with previous findings, we argue that most of the Q-III interactions can be attributed to reduced translational capacity at the restrictive temperature. Finally, reciprocal temperature shift studies were used to delineate TSPs for interactions between Q-III and vg (mid to late second instar), cp (about mid-third instar), Dfd (early third instar) and Dl (late second to mid third instar). We believe that these TSPs represent developmental intervals during which the respective gene products are utilized.

Genetic divergences between the wild mouse populations with various Robertsonian translocations from the Poschiavo Valley, Yugoslavia, Milan and the Apenninies, were estimated based on the mitochondrial (mt) DNAs. The mtDNAs isolated from the liver were analysed by agarose slab-gel electrophoresis after digestion with eight kinds of restriction endonucleases: BamHI, EcoRI, HindII, HindIII, PstI, HpaI, HpaII and BgII. These preparations were further used to make restriction maps, from which sequence divergence between each Rb variation was calculated to be 0·2–2·2%. These rather larger values appear to be in conflict with the present concept that the Rb variations occurred during the last several thousand years. Both, however, might be reconciled by assuming genetic introgression of the founder with a small number of Rb translocations into other subspecies populations genetically remote and the subsequent rapid accumulation of Rb translocations unique to each population due to an unknown mechanism occurring specifically in the intersubspecies hybrids between M. m. domesticus and the other M. m. subspecies. This was the case also in a new Rb (9.15) translocation obtained from Ogasawara Islands in Japan which was the intersubspecies hybrid between M. m. molossinus and M. m. domesticus.

Changes in brain size, body size and their co variance are reported from a long-term replicated directional selection experiment on body weight gain in rats. Two strains had been selected for increased and two for decreased weight gain between 3 and 9 weeks of age, and there were two randomly selected control lines. Selection produced significant changes in body weight in all selected lines. Divergence from the controls occurred in brain size in those strains selected for increased weight gain; no significant divergence was found for the strains selected for decreased weight gain. Divergence among unselected control lines suggests that genetic drift occurred in expression of brain size. Sexual dimorphism in response to selection results from sex differences in heritabilities and genetic correlations in relevant traits. In spite of considerable change in body size and brain size, no significant change in their covariation occurred either between the selection lines or between sexes. The relevance of these results to a brain and body size ‘scaling effect’ during evolutionary divergence is discussed.

We measured traits involved in physiological and behavioural thermoregulation in the 6 replicates of a selection experiment for large and small size (6-week weight) in mice, including control lines (18 lines in all). The observed genetic correlations between body size and thermoregulatory traits are consistent with a thermoregulatory advantage of large size, including decreased weight-specific food consumption and increased nest-building, with no change in body temperature. The differences in food consumption were closely paralleled by differences in amount of brown adipose tissue, strongly suggesting that much of the decreased efficiency of the small lines is due to heat production by brown fat. These results are consistent with available observations on natural populations, that selection for temperature adaptation probably has had some influence on body size in this species.

Genetic variation in the modulating effect of dietary sucrose was assessed in Drosophila melanogaster by examining 27 chromosome substitution lines coisogenic for the X and second chromosomes and possessing different third isogenic chromosomes derived from natural populations. An increase in the concentration of sucrose from 0·1% to 5% in modified Sang's medium C significantly altered the activities of 11 of 15 enzyme activities in third instar larvae, indicating that dietary sucrose modulates many, but not all, of the enzymes of D. melanogaster. A high sucrose diet promoted high activities of enzymes associated with lipid and glycogen synthesis and low activities of enzymes of the glycolytic and Krebs cycle pathways, reflecting the physiological requirements of the animal. Analyses of variance revealed significant genetic variation in the degrees to which sucrose modulated several enzyme activities. Analysis of correlations revealed some relationships between enzymes in the genetic effects on the modulation process. These observations suggest that adaptive evolutionary change may depend in part on the selection of enzyme activity modifiers that are distributed throughout the genome.

The partitioning of digestible energy intake on an ad libitum diet of standard mouse nuts was investigated in mice selected for high and low body weight at eight weeks and in an unselected control population. In selected mice aged from four to six weeks and housed at a temperature of 24·5 °C, almost all their energy intake could be attributed to basic maintenance and the deposition of extra protein and fat. Control mice, however, had an energy intake considerably in excess of their apparent maintenance and growth requirements. It was concluded that the unaccountable energy loss of the control line could be used to increase growth efficiency in the selected lines. The result is analogous to those obtained from studies on normal and obese mouse genotypes and indicates genetic changes in mechanisms controlling the conversion of food energy to heat.

Provision of a nest to reduce thermoregulatory heat production caused a minor reduction in energy intake and a corresponding decrease in the energy discrepancy. There was no effect on growth.

Nine diverse lines of cultivated barley (Hordeum vulgare) and 11 lines of its wild progenitor (H. spontaneum) were assayed for variation in their chloroplast DNA by digestion with ten restriction endonucleases. The cultivated lines exhibited a single cpDNA polymorphism, whereas the wild material exhibited five. The significantly lower level of diversity among the cultivated lines was unexpected because both cultivated and wild lines had been selected for comparable levels of diversity for nuclear encoded isozyme loci. These results suggest that the level of cytoplasmic diversity was markedly restricted during the domestication of cultivated barley.