At the present time attempts are being made to improve the nutritional value of wheat by increasing the content of certain essential amino acids, particularly lysine, in the proteins of the grain. Rye grain has a considerably higher lysine content than that of wheat. Consequently in the present work studies were made of the amino acid contents of the grains of the wheat variety Holdfast, the rye variety King II, the Triticale derived from these parental varieties and the seven lines in which, in turn, each pair of chromosomes of King II are separately added to Holdfast.

Rye chromosome I increased the lysine content of wheat by 8·7% and associated changes in the proportions of other amino acids suggest that this increase is meaningful. Rye chromosome I is in homoeologous group 5 and other reports have indicated a relationship between changed lysine content and another character determined by chromosomes of this group. Consequently there is a suggestion that group 5 chromosomes may be of particular significance in the determination of lysine content in wheat grains. Confirmation of this would lead to a more rational approach to breeding for higher lysine content.

Sarcina flava ATCC 540 (ade) and Micrococcus flavocyaneus ATCC 8673 (ade), two related micrococci, were transformed to prototrophy at frequencies as high as 0·02% and 0·005% of colony-forming units, respectively. Both of these organisms were transformed by selected prototrophic strains of Micrococcus lysodeikticus, M. flavocyaneus, S. flava and Sarcina lutea.

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.

The relations between the quantity of red eye pigment and related pteridine compounds of Drosophila melanogaster have been studied in a variety of genotypes, which include strains selected for high or low pigment content, various derivatives of these lines and also lines in which one or other of the major autosome pairs were represented by homozygous chromosome pairs, derived by random sampling from the base population and also inbred lines. The quantity of red pigment was defined by the optical density when whole heads were extracted in a suitable solvent, while the pteridines were separated by chromatography and their amounts estimated by means of their characteristic fluorescence.

The evidence from selection, inbreeding and chromosome sampling from the base population demonstrated the presence of substantial genetic variation for pigment content and amounts of related pteridines.

The genetic and biochemical properties of the selected lines differed according to the direction of selection. High lines remained heterozygous after many generations of selection and displayed dominance and epistasis in favour of higher pigment content in crosses to the unselected stock. Selection for low pigment content led to fixation of recessive effects, attributable to particular chromosomes. The dominance-recessive relationship in red pigment differences was also applicable to the associated pteridines.

The metabolic pattern in all lines with reduced pigment content is compatible with the assumption of reduced enzyme activity at particular steps of the pathway leading to the drosopterins (red eye pigments). The two steps accessible to study are subject to genetic variation in the base population, while inbreeding or selection for low pigment content leads to genetically fixed alterations at one or other of these steps. The genetic analysis was consistent with the biochemical evidence.

Increase in pigment content above the normal level, either by selection or chance fixation, is accompanied by correlated increase in all the precursors. Several alternatives are possible but it is suggested that this may be due to an increase in early precursors, before the stages which have been altered in the low pigment lines.

Attention is drawn to the similarity in genetic behaviour between pigment content and body size. Particular emphasis is laid on the value of selection as a means of creating biochemical differences which offer a basis for relating biochemical function and genetic behaviour.

Mice heterozygous for rump-white (Rw) have white hair in lumbo-sacral and caudal regions, although the tail-tip is sometimes pigmented. The homozygote is lethal in utero. No recombination has been found between Rw and the very closely linked spotting genes patch (Ph) and the viable allele of W (Wv). The compounds between these genes are all viable and fertile, although individual homozygotes are either lethal (Ph, Rw) or sterile and anaemic (Wv). It is concluded that they are non-allelic, but form a gene triplet. Close linkage between a cluster of dominant spotting genes and an angora gene in mouse and rabbit provide evidence for homology of part of linkage group II in the rabbit and part of linkage group XVII in the mouse.

The mutagenic effects of feeding calf-thymus DNA to larvae of Drosophila melanogaster have been studied on second chromosome recessive lethals, sex-linked dominant and recessive visibles and dominant autosomal visible mutations. While a positional specificity of DNA-induced lethals has been confirmed, no evidence has been obtained for a preponderance of visible mutations or for a specificity of phenotype among the visibles.

The effect of ultraviolet radiation (u.v.) on λ lysogens of exrA strains of Escherichia coli was studied. exrA strains could be lysogenized with, as well as support the vegetative reproduction of, λ. However, though spontaneous induction of λ occurred in exrA(λ) strain at 10% the frequency of exrA+(λ) strain, exrA(λ) strains were not induced by u.v. Because λ was not induced in exrA(λ) strains, lysogens of these strains were no more sensitive to u.v. than were non-lysogens.

The heat-inducible mutant λhcI857 could be induced in exrA strains at elevated temperatures. Furthermore, u.v. irradiation of exrA (λhcI857) strain did not prevent the heat induction of this λ mutant. The exrA mutation appeared to interfere only with the inactivation of λ repressor by u.v.

Among the exrA strains studied was strain Bs1(exr A uvrB). Whereas the λ lysogen of strain Bsl could not be induced by u.v. and was no more sensitive to u.v. than its non-lysogen, the exrA+uvrB(λ) derivative of strain Bsl could be induced by u.v. and was more sensitive to u.v. than its non-lysogen.

Evidence from a functional analysis of host-specificity mutants in merodiploids is presented which supports the suggestion that three genes, hss, hsr and hsm, are necessary for the expression of host-controlled restriction and modification. The host-specificity phenotype expressed by the merodiploids provides evidence that at least two genes, hss and hsr, are concerned in the expression of host-specific restriction of DNA and one of these genes, hss, is responsible for the strain specificity of the restriction enzyme. A class of modification-deficient mutants isolated from restriction-deficient, modification-proficient mutants, was also tested for complementation in merodiploids and the phenotype of these merodiploids provides evidence that at least two genes, hss and hsm, are concerned in the expression of host-specific modification of DNA and one of these genes, hss, is responsible for the strain specificity of the modification enzyme. How these three genes function at the molecular level is discussed in terms of models based on the interaction of subunits to form oligomeric enzymes.

Three new autosomal mutants of the milkweed bug, Oncopeltus, obtained by treatment with ethylmethane sulphonate, are described and compared with the two other previously known variants. Preliminary data are given on the results of testcrosses and of chromatographic analysis of some pteridene pigments.

Twenty-three exotic strains of four species of Neurospora (N. crassa, N. sitophila, N. intermedia and N. tetrasperma) were grown in minimal medium and their enzyme phenotypes were compared. The exotic strains did not differ substantially with respect to the specific activities of the biosynthetic enzymes, ornithine transcarbamylase (OTC), carbamyl phosphokinase and aspartate transcarbamylase. Exotic strains of N. crassa and N. sitophila were crossed with laboratory mutants of N. crassa to determine whether there were significant differences among the exotic strains in the gene complexes underlying their enzyme phenotypes. Most of the exotic strains carried similar OTC structural genes and similar genetic modifiers of OTC activity: their OTC structural genes were expressed normally in the genomes of the parent strains, in the alien genomes of standard laboratory mutants and in the mixed genomes of parent × mutant hybrids. One exotic N. crassa carried a distinctive OTC structural gene that elevated OTC activity when transferred into the genome of a standard laboratory mutant. A second exotic N. crassa carried distinctive genetic modifiers of OTC activity: two mutations, c- and hi, interacted in the exotic parent to normalize OTC activity and rate of growth, but hi led to extremely high OTC activities and to a reduction in rate of growth when separated from c- by interstrain recombination.

Evidence is given that me-7 and me-9 are separate but contiguous gene loci.

The pattern of polarized recombination throughout the me-7 me-9 region indicates the location of a recombinational discontinuity between the known me-7 alleles and the known me-9 alleles.

Recombination events may include sites in both genes but such events are not preferentially associated with parental combinations of flanking markers.

Recombination events extending into both genes provide an extra criterion for the ordering of the sites within the me-7 locus. The order so obtained confirms that deduced from the flanking markers of me+ recombinants from me-7 × me-7 crosses.

In me-7 × me-9 crosses but not in me-7 × me-7 crosses, the map order derived on the assumption that single exchanges are more frequent than apparent triple exchanges is the reverse of that derived from prototroph frequencies. It is concluded that the former criterion is more likely to have provided the correct order and the anomalous prototroph frequencies reflect the polarity of gene conversion within me-7.

A general expression is derived for the variance of time to fixation of a neutral gene in a finite population using a diffusion approximation. The results are compared with exact values derived by matrix methods for a population size of 8.

A genetic fine-structure experiment on Drosophila melanogaster is described, which makes use of a lethal selective system which permits survival only of recombinants in the ma-l region, including exchanges between site mutants of ma-l. On the basis of prior mapping information, the experiment was designed to select for ma-l double mutant recombinants. Utilizing a pair of complementing ma-l mutants, double mutant meiotic products were recovered whose complementation properties provide independent support for the single-cistron, allele complementation model of organization of the maroon-like region inferred from other experiments described earlier.

Eight experimental populations of Drosophila pseudoobscura were made in laboratory population cages. All were polymorphic for ST, AR, CH, and PP gene arrangements in their third chromosomes, and all the chromosomes were of the same geographic origin. The initial frequencies of the gene arrangements were, however, different in the different populations. Natural selection has caused frequency changes in all the populations, from which we have attempted to infer the adaptive values of the different karyotypes. There was no evidence that the adaptive values were different in the populations begun from different initial frequencies of the inversions, although our ability to demonstrate such differences is severely limited. The selection process in these populations has been complex, and the simple model of constant adaptive values does not fit.

In finite populations, loci maintained segregating by hétérozygote superiority will be disturbed from their equilibrium positions by genetic sampling and the mean fitness of individuals will consequently be reduced. A general expression for this reduction is obtained for the segregation of two alleles. If the probability of continued segregation at the locus is high, the reduction tends to 1/4N, irrespective of the strength of selection, where N is the effective population size. This will always be much less than the segregation load. If n alleles are segregating, so that all heterozygotes have the same fitness, the reduction tends to (n−1)/4N.

Embryos were recovered 3½ days post coitum from females of three replicate large- and small-selected Q-strain lines, together with their unselected control lines. Selection had been carried out by D.S. Falconer, resulting in large and small lines which differed two-fold in adult body weight. Females of the large lines yielded significantly more embryos than those of the other lines. Embryo cell number showed significant heterogeneity among replicates, but was similar in large, small and unselected lines. The data are not consistent with the hypothesis that the divergence in adult body weight is due to a uniform difference in rate of cell division throughout development.

Frequency distribution of the length of time until fixation (excluding the cases of eventual loss) of a selectively neutral mutant in a finite population was obtained. With 4Ne generations (Ne, effective population size) as the unit length of time, the distribution has mean μ1 = 1, standard deviation σ = 0·538, skewness γ1 = 1·67 and kurtosis γ2 = 4·51 (see Fig. 1).