Estimates of the activities (Vmax) of six enzymes involved in de novo fat synthesis were made in replicated lines of mice differing in fat content. These lines had been selected high and low for 20 generations with three replicates each of Fat, Control and Lean lines and for a further eight generations high and low as an unreplicated line. The activities of ATP-citrate lyase (ACL), acetyl-CoA carboxylase (ACC), fatty acid synthetase (FAS), cytoplasmic malate dehydrogenase (MDH), malic enzyme (ME) and pyruvate kinase (PK) were determined in vitro in both liver and gonadal fatpad tissues taken at ages five and ten weeks. The activities of ACL, ACC, FAS and ME were significantly higher in the Fat than the Lean lines, and the differences were more pronounced at the earlier age and in the gonadal fatpad where activities in the Fat lines were higher by factors of 3·5, 2·4, 2·5 and 3·5 respectively. The activity of PK was unchanged in each tissue. MDH activity was significantly lower in adipose tissue in the Fat lines than the Lean lines at age ten weeks but not at age five weeks or in liver tissue. Results from replicates indicated that random genetic drift affected enzyme activities but nevertheless significant changes in activity were associated with the direction of selection. The changes in enzyme activity reported here are similar to those known to be associated with major mutations causing obesity in mice.

A hypothesis has been tested that alterations in the molecule of histone H1 are capable of influencing quantitative traits of an organism. Two pairs of isogenic lines were constructed by selfing of plants kept heterozygous either for allelic variants of histone H1 subtype 1 (His1 gene) or for allelic combinations (haplotypes) of closely linked genes of H1 subtypes 3, 4, 5 and 6 (gene cluster His(2–6)). After 19 and 15 generations of selfing, respectively, expectation of the length of chromosome which remained heterozygous has comprised 2·6 cM near Hisl and 3·5 cM near His(2–6). The third pair of isogenic lines was obtained as a result of two successive intracluster cross-over events bordering the gene of the subtype 5 (His5). In each pair of isogenic lines there have been revealed some statistically significant differences between mean values of a number of quantitative traits.

Levels of transcripts produced by a heat shock protein 70 (hsp70)-antisense white transgene in Drosophila were measured after single and multiple heat shocks to determine whether the hsp70 promoter could produce sustained high levels of transgene transcripts. A single heat shock resulted in typical highly inducible levels of RNA, but the amount of antisense RNA was substantially reduced after multiple heat shocks. Endogenous hsp70 mRNA levels were also less abundant after multiple heat shocks as compared to a single heat shock. The hsp70 promoter is unsuitable for use in fusion gene constructs for long term expression studies where repeated heat shocks are required.

In Takahata & Slatkin (Genetical Research 1983, 42, 257–265), two sentences should be read as:

but, in contrast, the configuration of the genome and the mode of transmission both make a large difference (on page 257, lines 11–12 up)

Contribution no. 1528 from the National Institute of Genetics, Mishima, Shizuokaken 411, Japan (on page 264, above REFERENCES).

Bacterial hybrids were produced to contain genetic material of Salmonella typhimurium, Escherichia coli, S. montevideo and S. abony origins. Analyses by transduction provide evidence that 6% of the original typhimurium genome has been replaced in the production of these hybrids. Although a number of biosynthetic pathways are affected by this gene substitution, the growth rate of these hybrids in minimal medium is unchanged. Supporting evidence for the close relatedness between S. typhimurium and the other three species is not observed in recombination studies. Available results favour the concept that differences in base sequences are responsible for the low frequency of recombination obtained in heterologous crosses.

Models of variability in quantitative traits maintained by a balance between mutation and stabilizing selection are investigated. The effects of mutant alleles are assumed to be additive and to be randomly sampled from a stationary distribution. With a two-allele model the equilibrium genetic variance in an infinite population is independent of the distribution of mutant effects, and dependent only on the total number of mutants appearing per generation. In a finite population, however, both the shape and standard deviation of the distribution of mutant effects are important. The equilibrium variance is lower when most of the mutational variance is contributed by few genes of large effect. Genes of small effect can eventually contribute substantially to the variance with increasing population size (N.) The equilibrium variance can be higher in a finite than an infinite population since near-neutral alleles can drift to intermediate frequencies where selection is weakest. Linkage leads to a reduction in the maintained variance which is small unless linkage is very tight and selection is strong, but the reduction becomes greater with increasing N since more mutants segregate. A multi-allele model is simulated and it is concluded that the two-allele model gives a good approximation of its behaviour. It is argued that the total number of loci capable of influencing most quantitative traits is large, and that the distribution of mutant effects is highly leptokurtic with the effects of most mutants very small, and such mutants are important in contributing to the maintained variance since selection against them is slight. The weakness of the simple optimum model is discussed in relation to the likely consequences of pleiotropy.

The b locus of Ustilago maydis is both an incompatibility locus and a pathogenicity locus. There are several different b factors, and they are randomly distributed and equally frequent in the natural population. A sample of 62 lines contained 18 b groups and permitted an estimate of no more than 25 b groups in the natural population. All lines within the same b group are indistinguishable in their mating behaviour. No linkage was detected between b and any of the four biochemical markers tested. No intrafactor recombinants at b were found among more than 6700 progeny. Differences in degree of pathogenicity between solopathogenic diploids and comparable haploid by haploid crosses were detected.

This study investigated genetic variation in growth and final size in relationship to differences in heritabilities under good and poor feeding conditions. Heritabilities of growth and final size were estimated for several traits under ad libitum and restricted feeding conditions. A 30% feed restriction from hatching to 44 days of age in Japanese quail chicks decreased body weight and tarsus length at 44 days of age and the length of the third primary covert feather at 24 days of age relative to controls fed ad libitum. Wing length at 44 days of age was not significantly different for ad libitum fed and restricted quail. Genetic variances for body weight and tarsus length were very large throughout growth which resulted in heritability estimates close to one for these traits. The genetic correlations among feeding treatments were low, indicating that different genes were affecting growth under the two treatments. Growth was described by the components: asymptote, growth period, and shape of the growth curve following the modified Richards growth curve model (Brisbin et al. 1986). Tarsus length, which had high heritability of the parameter ‘growth period’ of the model, tended to display a higher heritability under the restriction than under ad libitum feeding. Body weight and feather length, which had either no heritable or low heritable ‘growth periods’ estimates, tended to be more heritable under ad libitum feeding. The shape parameter of the growth curve was not heritable for any trait, except tarsus length under restricted feeding.

1. Hairless (H), a dominant mutant of Drosophila melanogaster, affects the chaetae.

2. Various ‘intensities’ of effect are interpreted as representing different times in chaetal development at which deficiency of ‘+H substance’ is encountered. ‘Temperature effective period’ studies confirm this view.

3. The chaetae at different sites are liable to characteristically different ‘intensities’ of effect. In other words a particular site tends to be affected at a limited time in its development. If it is supposed that a single period of deficiency of +H substance accounts for effects on all chaetae, then it follows that development of the various chaetae is asynchronous. Some histological observations tend to support this prediction.

The implications of asynchrony with respect to pattern formation are discussed.

4. It is argued that the source of +H substance may be an endocrine organ, the ring-gland.

5. Two modifiers Su-H and E-H, whose expression and linkage relations are described in detail for the first time, are, it is suggested, respectively ‘constitutive’ and ‘super-repressed’ mutations of a ‘regulator’ locus controlling negative feed-back on the +H locus.

Studies of lines of mice selected for body mass have shown that there is a significant genetic component affecting this trait although the nature of the genes involved remains to be elucidated. Using replicate lines of mice, our studies have shown that two different variants of the mouse ornithine decarboxylase (ODCase) gene have been selected in replicate lines of mice selected for high and low lean body mass respectively. One variant is associated with an increased peak of ODCase activity in embryos (10–13 days of gestation) in all high mass lines and with a restriction fragment length polymorphism of the expressed gene. The increased ODCase activity coincides with increased ODCase mRNA levels in the high mass selected lines. These results provide evidence implicating ornithine decarboxylase as a major factor in cell growth, and as a candidate ‘trait gene’.

A defined medium for Physarum polycephalum plasmodia has been devised containing glutamic acid, glycine, methionine, biotin, thiamine, glucose, salts and haematin, which supports good growth on agar plates of many different strains. Tests on this medium have revealed a requirement for valine in some plasmodia formed by homothallic progeny (mthapt-l+) from the cross a (mt1apt-l+) × APT1 (mthapt-l−). The valine requirement was also inherited among heterothallic progeny of this cross and its segregation was followed in several heterothallic crosses. To explain the results it is proposed that valine synthesis requires the presence of dominant alleles at either of two unlinked loci and that only plasmodia homozygous for recessive alleles at both loci are valine dependent. In some crosses studied only one pair of alleles is segregating and valine requirement thus provides a useful genetic marker, and the first reported nutritional marker in P. polycephalum. The value of crosses with apt− mutants for both the detection and analysis of plasmodial markers is demonstrated and discussed.

A number of acridines have been tested for ability to inhibit conidia of strains of Aspergillus nidulans. The effectiveness of any one acridine in growth inhibition and killing involves interaction of genotype and conditions of treatment such as temperature, pH, treatment medium and light intensity. Mutant alleles which confer growth resistance to acriflavine are selective in their actions towards other acridines, may differ in their dominance relationships with different acridines and are even selective with regard to the conditions under which they confer acriflavine resistance. Certain pairs of acridines, used simultaneously, show additive effects, potentiation, or annulment by one of inhibition caused by the other.

Some of these findings have been applied in a study of factors affecting acridine-induced mutation in Aspergillus conidia. Under conditions which permit metabolism, acriflavine induces a high frequency of unstable morphological variants. One such variant has been shown to be a disomic. Using a system of reversion from auxotrophy to prototrophy, acriflavine-induced mutation has been obtained both with high light intensities and in the absence of light. In the latter case recombination as a feature of the mutation process is excluded.

In Paramecium aurelia, syngen 4, gene ts21m, which is shown to segregate normally and independently of two other genes: ts111 and m1; is closely linked to gene ts401. The frequency of then recombination is of the order of a few per cent. Genetic analysis was carried out to confirm the genotypes of both double mutants and wild-type recombinants among F2 clones from crosses ts21m × ts401. This is the first case of linkage so far reported in P. aurelia.

We have investigated the effect of the ribosome-targeted antibiotic kasugamycin (ksg) in Podospora anserina. While ksg inhibits both growth and sporulation, it has a stronger inhibitory effect on the sporulation process. It was previously reported that sporulation of Podospora could be impaired when ribosomes translate with a too high accuracy, and since ksg was demonstrated to increase the ribosomal accuracy in E. coli, we wondered whether it would act similarly in Podospora. As a first approach we have isolated two mutations at different loci, Ks1 and Ks2, that increase the resistance to ksg at the level of both growth and sporulation. Interestingly Ks1−1 also confers a decreased resistance to paromomycin, which is a mistranslation inducer. Characterization of Ks1−1 and Ks2−1 mutants suggests that they could be ribosomal mutants.

Seventeen highly-inbred lines of Drosophila melanogaster extracted from an M′ strain (in the P/M system of hybrid dysgenesis) were studied for their cytotype and the number and chromosomal location of complete and defective P elements. While most lines were of M cytotype, three presented a P cytotype (the condition that represses P-element activity) and one was intermediate between M and P. All lines were found to possess K.P elements and only eight to bear full-sized P elements. Only the lines with full-sized P elements showed detectable changes in their P-insertion pattern over generations; their rates of gain and of loss of P-element sites were equal to 0·12 and 0·09 per genome, per generation, respectively. There was no correlation between these two rates within lines, suggesting independent transpositions and excisions in the inbred genomes. The results of both Southern blot analysis and in situ hybridization of probes made from left and right sides of the P element strongly suggested the presence of a putative complete P element in region 1A of the X chromosome in the three lines with a P cytotype; the absence of P copy in this 1A region in lines with an M cytotype, favours the hypothesis that the P element inserted in 1A could play a major role in the P-cytotype determination. Insertion of a defective 2 kb P element was also observed in region 93F in 9 of the 13 M lines. The regulation of the P-element copy number in our lines appeared not to be associated with the ratio of full-length and defective P elements.

1. The DNA contents of twenty-eight different species and forms of Chrysanthemum have been measured by photometry. It is shown that there are large differences in DNA content between some species with identical chromosome numbers.

2. The DNA contents of natural polyploids are frequently not those expected when comparison is made with diploid forms of the same species. The DNA contents of induced polyploids are those expected.

3. Chromosome length and volume are positively correlated with DNA content.

4. The relationship between chromosome number, chromosome size, DNA content and gene number is considered, and it is suggested that the differences in DNA content may result from the presence of differing amounts of genetically inactive DNA in the chromosomes.