Strains of Aspergillus nidulans with a duplicate segment are mitotically unstable; they produce phenotypically improved variants following deletions in either duplicate segment, and morphologically deteriorated types. The number of variants produced is characteristic of each duplication strain under the same conditions. After ultraviolet treatment two variants, one more stable and the other less stable than the original strain, were selected. Genetic analysis showed that the increased instability in the less stable variant was due to a translocation involving linkage groups V and VIII. The increased stability of the more stable variant was due to a recessive factor (stf–1) located in linkage group VIII. In the homozygous condition this factor also reduces the number of sectors in a diploid strain. The possible genetic mechanisms explaining the instability alterations are discussed.

The frequency and nature of the changes in ‘state’ of the mouse X-chromosome controlling element (inactivation centre) have been investigated on an inbred background. The results indicate with near-certainty that meiotic crossing over is the responsible mechanism and that the frequency of recombination between the T(1; X)Ct breakpoint and the locus of the controlling element is approximately 3%. Maize-type ‘changes in state’ may occur under other experimental conditions. The data do not distinguish on which side of the autosomal insertion the element lies but when combined with observations of other investigators suggest that the location must be on the Mo-Ta side and very close to Ta.

An amber mutation was created in the CAT gene of plasmid vector pACYC184 and this modified plasmid was fused with the Streptomyces vector pIJ702 for use as an indicator for the identification of Streptomyces strains carrying nonsense suppressor tRNA mutations. The resulting hybrid plasmid pGM1109 was introduced into the chloramphenicol-sensitive mutant M252 of Streptomyces lividans. Chloramphenicol-resistant colonies were isolated and characterized. None of them was a nonsense suppressor mutant. The failure to obtain such mutants is discussed on the basis of codon usage in streptomycetes.

Data are presented which support the conclusion that in the flecked translocation, T (1; X) Ct, there is a spread of inactivation into both sides of the autosomal region inserted into the X. This would indicate that both parts of the divided X are subject to the X-inactivation process. The data also demonstrate that the inactivation of autosomal genes lying near each end of the insertion are modified by the X-chromosome controlling element system, Xce. Since the element modifies the heterozygous expression of X-linked genes on one side of the insertion, it would therefore be expected that it similarly modifies the heterozygous phenotypes of those on the other side. The data thus support the concept that the controlling element is the master gene, receptor site or inactivation centre which regulates the X inactivation process.

XY and XX doublesex D. melanogaster, expressing variable intersexual phenotypes, were compared for their pheromone levels (e.g. 7, 11-heptacosadiene, the main excitatory pheromone of females, and vaccenyl acetate, an inhibitory compound produced only by males). Despite the intersexual phenotype and the presence of female traits, the pheromone patterns of the homozygous dsx mutants, XY as well as XX, were similar to those of heterozygous males. Female-specific dienes were never found in significant amounts in such flies, which often showed significant amounts of the male-specific acetate and triggered very reduced levels of male courtship wing vibration.

Two separate, but interacting, genetic systems underlie the variation in seasonal cycles among members of the Chrysoperla carnea species-complex. The two systems are expressed as all-or-none reproductive responses to photoperiod and prey (i.e. short-day/long-day requirement for reproduction versus long-day reproduction and prey requirement for reproduction versus reproduction without prey). In each case the alternative to reproduction is reproductive diapause. The photoperiodic responses are determined by alleles at two unlinked autosomal loci. The expression of dominance by the alleles at these loci varies among geographical populations. The genes that determine the photoperiodic responses also act as suppressors of the genes that govern responsiveness to prey. An autosomal, polygenic system, with a threshold for the expression of diapause, determines responsiveness to prey. The two genetic systems are important to seasonal diversification and speciation within the C. carnea species-complex.

A systematic search for correlations between numerous minor skeletal variants in the mouse showed that these are few in number and feeble in extent. This apparent lack of integration is probably due to the fact that these characters are at the extreme limits of genetical determination and so are overwhelmingly influenced by chance in their manifestation.

The issue of incorporating the good alleles from two homozygous populations of a cross-fertilizing species into a single improved population was investigated assuming independent assortment, no epistasis, and either complete dominance (of the favourable or the unfavourable alleles) or additive genes. The selection limit in the foundation stock is a function of the effective population size (N), the proportion (x) contributed by the better source population (P1), the difference in relative fitness between single locus homozygotes and the proportion of loci (that will segregate in the foundation stock) fixed favourably in P1. In real life the last two of these are never known. We therefore focused on the response limits given x = 0·5, 0·75, 0·875 or the optimum value of x (which is a function of the other three parameters). Our general finding was that in situations where N is large enough so that a major portion of the potential can be achieved, the F2 population should be used as the foundation stock when the two source populations do not differ greatly in performance; but when one population performs considerably better than the other, the first backcross (but not second backcross) would be the choice.

Following Moran's (1962) method, it was shown that the fixation probability of a mutant gene is not altered by the subdivision of a population into partially isolated colonies, if the following conditions are met; fitness is additive, samplings and selection is done separately in each colony, and migration between colonies does not change the gene frequency in the whole population. This conclusion was checked by simulation experiments.

Cockerels singly or doubly heterozygous (t1/ +, t2/ + and tl/t2, respectively; collectively heterokaryotypic, HTK) for two different Z-autosome translocations (t1, t2) produce an array of chromosomally balanced and unbalanced spermatozoa owing to adjacent segregation and nondisjunction at the first meiotic division. This study addresses the developmental capacity of embryos derived from matings of control ( + / + ) and HTK (tl/ +, t2/ +, tl/t2) cockerels with hens bearing normal chromosome complements (+ /W).

Estimates of the hatchability of fertile eggs sired by + / +, tl/ +, t2/ + and tl/t2 cockerels were 82·8%, 43·0%, 41·3% and 10·9%, respectively. Approximately 75% of the mortality observed in embryos sired by HTK cockerels occurred by four days of incubation. Developmental arrest generally occurred earlier in embryos sired by t2/+ and tl/t2 cockerels than in those by tl/ + cockerels. These differences reflect variation in the degree of embryonic chromosome unbalance expected among embryos of the different sire groups. The pattern of mortality after three days was similar in embryos sired by HTK cockerels. In control embryos, mortality was highest on days 20–21 of incubation.

Chromosome analysis of 16/18 h embryos, day 1/5 embryos and hatched chicks sired by HTK cockerels revealed that most, if not all, chromosomally unbalanced embryos died during development; the majority before three days of incubation. Partial monosomy for chromosome one was found to be more deleterious to embryonic development than partial trisomy.

Z-(ll)-pentacosene, Drosophila virilis sex pheromone, is predominant among the female cuticular hydrocarbons and can elicit male courtship behaviours. To evaluate the genetic basis of its production, interspecific crosses between D. novamexicana and genetically marked D. virilis were made and hydrocarbon profiles of their backcross progeny were analysed. The production of Z-(ll)-pentacosene was autosomally controlled and was recessive. Of the six D. virilis chromosomes only the second and the third chromosomes showed significant contributions to sex pheromone production, and acted additively. Analysis of recombinant females indicated that the locus on the second chromosome mapped to the proximity of position 2–218.

Pseudomonas arvilla mt-2 (ATCC 23073) has been shown to harbour a transmissible plasmid which codes for the degradation of benzoate and m-toluate. Plasmid-borne genetic information codes for the conversion of these compounds to catechol then the assimilation of catechol via the meta cleavage pathway.

P element mutagenesis was used to contaminate M strain second chromosomes with P elements. The contaminated lines were compared to uncontaminated control lines for homozygous and heterozygous fitness and its components. Mean homozygous fitness, viability and fertility of chromosome lines contaminated with P elements is decreased relative to the uncontaminated control lines by, respectively, 55, 28 and 40%. Variance among contaminated homozygous lines of total fitness increases by a factor of 1·5, variance of viability by a factor of 5·9, and variance of fertility by a factor of 1·9, compared to variance of these traits among the population of uncontaminated homozygous chromosomes. Estimates of P-element-induced mutational variance among second chromosome lines for homozygous fitness, viability and fertility are, respectively, 2 × 10−2, 5 × 10−2 and 2 × 10−2. This magnitude of mutational effect is equivalent, in terms of incidence of induced recessive lethal chromosomes and D:L ratio, to a dose of approximately 1·0–2·5 × 10−3 m EMS. The distributions of fitness traits among M-derived second chromosome homozygous lines contaminated with P elements are remarkably similar in many regards to distributions of fitness and viability of chromosomal homozygotes derived from natural Drosophila populations. It is possible that a proportion of the fitness variation previously observed (reviewed by Simmons & Crow, 1977) following homozygosis of wild chromosomes was not present in the natural populations, but was generated by P-element transposition during the chromosome extraction procedure. P-element-induced fitness mutations appear to be completely recessive. Implications for models of evolution of transposable elements are discussed.

Escherichia coli K-12 mutants resistant to glutamyl-γ-methyl ester were isolated. A mutation leading to resistance of up to 1·4 mg/ml of the methionine analogue maps at min 63 and is 13% cotransducible with serA indicating an alteration in the metK gene. Another mutation leading to resistance to 3 mg/ml of the analogue and cross-resistance to other amino acid analogues maps at min 87. This mutation, which has the phenotype of MetJ−, is shown to be situated between the glpK and metB genes and thus indicates a different gene order from the published one.

The accumulation of deleterious mutations in a finite diploid selfing population is investigated. It is shown that the conditions for accumulation are very similar to those for the accumulation of mutations in an asexual population by ‘Muller's ratchet’. The ratchet is likely to operate in both types of population if there is a large class of slightly deleterious mutations.

The distribution of sex-determinants in field populations of Musca domestica domestica L. was studied in 62 samples of flies collected at 53 sites (animal farms) between 1975 and 1981 in an area stretching North–South from Denmark (+ Iceland) to Sicily.

Karyological observations and genetic analyses demonstrated the existence of three types of population along a latitudinal cline. Populations of Northern Europe were of the standard type (XX females and XY males) with the Y chromosome determining sex. Those of Central and Southern Italy from sites below 100 m.a.s.l. (metres above sea level) were autosomal (XX females and males), sex in them being determined by autosomal sex-determinants for both femaleness and maleness. In the large intermediate zone the populations were mixed and had several karyotypes in both sexes. In this zone an altitudinal gradient was also observed, with autosomal determinants less common at higher altitudes. Genetic tests showed, in the autosomal and in the mixed populations, the presence of two autosomal male factors: M III, the most common, on autosome III and M II, on autosome II.

The gradient in sex determinants found in flies of Western Europe appears to be a dynamic phenomenon of relatively recent origin. Both climatic influence and selective pressure with insecticides have probably contributed towards the micro-evolution of populations with different sex-determinants in the houseflies of the area studied.

In order to test the feasibility of preservation, of genetic stocks of mice by storage in liquid nitrogen, mouse embryos at the 8-cell stage, were frozen and stored in liquid nitrogen at – 196 °C under increased radiation exposures of 1·8×, 9× and 84× background levels for periods of 6–8 months, 10–12 and 27–29 months, the 1·8 × level being regarded as a control. Their survival rates to the blastocyst stage, and after transfer to recipient females, to foetal or liveborn stages were then compared with those of unfrozen or short term frozen control embryos. The freezing process per se caused a marked loss of viability, in comparison with the unfrozen controls, but at the 1·8× radiation level there was then no further loss in viability even at the longest storage time (27–29 months). Similarly, at the 9× radiation level there was no loss of viability during storage up to 29 months, but at the 84× level the proportions of implanted embryos and live foetuses were slightly reduced. It was not clear if this was a true effect of radiation, since it was not related to time of storage. Considering all groups, about 20–30% of the embryos originally frozen were recovered as foetuses or liveborn young. It is concluded that the preservation of genetic stocks by storage in liquid nitrogen is a feasible proposition.