Two linear models have been devised and applied to the study of the distribution of human male chromosomes on the metaphase plate in preparations from lymphocyte cultures not treated with spindle poisons. Using these it has been found that the chromosomes are approximately distributed around a centre of symmetry and that the lines joining the centromeres of homologous chromosomes (i.e. segments) have the centre of symmetry approximately at their mid-point. Thus each chromosome mirrors the position of its homologue relative to the centre of symmetry. The position of each chromosome in the metaphase plate was found to be approximately constant relative to the centre of symmetry and the other chromosomes. The significance of these findings is discussed in relation to the hypothesis on the distribution of the chromosomes in interphase nuclei and to data on acrocentric associations, acrocentric-non-acrocentric associations and the frequency of the most common translocations.

Some yellow alleles which show full expression of the mutant phenotype have behavioural defects, including reduced locomotor activity and a low level of male competitive mating success. Other yellow alleles produce pattern mosaics in which some cuticular structures are yellow and others wild type within the same individual. The pattern mosaic expression of these alleles extends to behaviour. Mosaicism in respect of the different pleiotropic effects reveals something about the possible mode of action of this locus on behaviour.

The wild-type N group plasmid RN3, which is phenotypically Res+ Mod+(RII) is not eliminated by thymine starvation of its bacterial host. Derivatives of RN3 selected for the Res− phenotype are eliminated. The presence or absence of the RII modification specificity does not affect thymineless elimination of RN3 Res− plasmids. A Res−Mod(am) RN3 mutant is not eliminated by thymine starvation from either amber suppressing or non-suppressing hosts, suggesting that it carries a cryptic mutation in a novel genetic locus required for elimination. Thymineless elimination is shown to be recA+-dependent and the presence of the X group plasmid R6K significantly inhibits elimination of RN3 Res−Mod+. However, since R6K has no effect on two other plasmid-mediated functions of UV protection and UV-induced mutagenesis, which are also recA+-dependent, it would appear that elimination is determined by a separate plasmid gene than that encoding the UV functions. This is confirmed using derivatives of another N group plasmid R390, which eliminate but which have lost the ability to increase UV-induced mutagenesis in their host.

Experiments have been performed to show that PGM polymorphism for the two common electrophoretic allozymes, PGMA and PGMB, in Drosophila melanogaster has adaptive value. Firstly, the allele frequencies converge to the same equilibrium value in six experimental populations. Secondly, density-dependent selection operates. Thirdly, the relative fitness of the three genotypes varies in modified culture media. PGM polymorphism is maintained by frequency-dependent selection and heterotic selection: the first mechanism operates to reach equilibrium frequency, the second cooperates to maintain it. The experiments performed with modified culture media favour the view that the two allozymes have different affinities for two components which are present in the nutritional environment. These components may be either substrates or other factors involved in the reaction catalyzed by PGM.

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.

Twenty-four cold-sensitive (prototrophic) mutants were isolated after UV mutagenesis of protoplasts of the fungus Podospora anserina. Genetic analysis of these mutants was performed in order to detect those among them which were most likely to be impaired in translational fidelity. The 24 mutations belonged to 24 different genes. One half of the mutants were pleiotropic and displayed an altered phenotype: growth rate at the permissive temperature, germination of the spores, fertility and/or sporulation. Nine mutants differed from wild-type in their resistance levels to cycloheximide, trichodermin and/or paromomycin. Several mutations were linked to known ribosomal loci. Two mutations behaved like informational antisuppressors: one is allelic to the previously described As3 gene and the other one defines a new antisuppressor gene, AS6.

The mutations which block lycopene cyclization and those which stop substrate transfer along the carotene pathway are very closely linked in Phycomyces. Simultaneous blocking of both processes commonly results from single exposures to mutagens; and both blockings may be simultaneously removed after a second exposure. The frequencies of different kinds of mutants after treatments with the mutagens N-methyl-N′-nitro-N-nitrosoguanidine and ICR-170, their reversion patterns, and recombination analyses indicate that lycopene cyclization and substrate transfer are governed by separate segments of a single bifunctional gene.

The alcohol dehydrogenase (ADH), glutamic oxaloacetic transaminase (GOT), aminopeptidase (AMP), endopeptidase (EP), and esterase (EST) zymogram phenotypes of Chinese Spring wheat, Betzes barley, Chinese Spring-Betzes heptaploids, and a number of presumptive Betzes chromosome additions to Chinese Spring were determined. It was found that four disomic chromosome addition lines could be distinguished from one another and from the other three possible lines on the basis of the zymogram phenotypes of these isozymes.

The structural gene Adh-H1 was located in Betzes chromosome 4, the genes Got-H2 and Amp-H1 in chromosome 6, and the gene Ep-H1 in chromosome 1. These gene locations provide evidence of homoeology between Betzes chromosomes 4, 6, and 1 and the Chinese Spring chromosomes of homoeologous groups 4, 6, and 7, respectively.

Meso-tartrate utilizing and resistant (mT+) recombinants were produced readily in transductions from an mT+ donor strain to 42 naturally occurring meso-tartrate non-utilizing and sensitive (mT−) recipient strains of Salmonella typhimurium, and were produced, sometimes as frequently, in interbiotype crosses between different pairs of strains from the mT− biotypes 2, 18, 26 and of the FIRN group (biotypes 30 and 32). These findings suggested that the sites of the mta mutations were independent in strains from the different mT− biotypes and were in agreement with their probable different lines of descent. Intrabiotype crosses indicated genetic homogeneity among strains of biotype 26 and among strains of biotype 30; on the other hand, they suggested that in each of the biotypes 2, 18 and 32, a minority of strains had mta mutations present at different intragenic sites from those of the majority of strains. The derivations of the strains of the minority types are discussed.