The genetical and developmental aspects of six dumpy mutants of Drosophila melanogaster have been investigated. The mutants obm, lm and olv (possibly alleles), lv, lv1 and lvI (possibly alleles) were known to be lethal when homozygous. Previously the lethal effect has been treated as a uniform effect. However, the lethal stage is not the same for all homozygotes, being egg/larval (E/L) for the three lv alleles, egg (E) for olv, larval/larval ecdysis (L/L) for lm and E/L and larval (L) for obm. Not all heterozygous combinations are lethal, i.e. obm/lm and obm/lvI are not lethal. Phenotypically the lethal heterozygotes fall into two patterns: (i) combinations not involving the allele obm and (ii) combinations involving obm. In the former, the mutant with the developmentally later expression is ‘dominant’ to the mutant with the developmentally earlier expression. In the latter, the genotypes manifest different proportions of individuals at the lethal stages E, E/L and L. Previous observations suggested that the lethality of the homozygote obm/obm was associated with the presence of an independent lethal in the stock. Observations presented here suggest that the lethality is a function of the obm allele itself. Complementation between some of the lethal mutants is not in accordance with the general rule for dumpy that compounds manifest the traits they have in common.

The sul gene of B/rw (Witkin) and 26 independently isolated sul mutants were examined for their suppression of radiation sensitivity. The suppressed lon gene was demonstrated by transducing it into a K12 proC recipient. The sul gene of B/rw and all but one of the B/r mutants was found to be linked to a gene controlling azide resistance. Transduction data established the order of markers as leu azi mutT sul. One B/r mutant was found not transducible with azide resistance, sul mutations were found to suppress the capsular polysaccharide production of lon strains.

The effect of dietary supplements of individual l-amino acids on the expression of the eyegone and eyelessK mutants of Drosophila melanogaster are compared. In both mutants, eye size is reduced by excess levels of tryptophan, phenylalanine and methionine, and in each case the effects are independent of metabolic competition for pyridoxal phosphate. A dietary interaction involving methionine and UNA can be demonstrated in the eyK strain, but the mechanism of action of this amino acid is obscure. Tryptophan metabolism is examined in detail. Although both tryptamine and serotonin have significant effects, the action of tryptophan on eye development is largely independent of its metabolic products. Conversely, the effect of dietary supplements of certain catecholamines is consistent with the action of phenylalanine. The action of certain metabolic inhibitors provides additional support for the suggestion that the catecholamines have an important effect on morphogenesis in the eye imaginai disks. Eye development is also affected by increasing concentrations of γ-amino-butyric acid, and this, taken together with the effect of the catecholamines and indolalkylamines, suggests that physiological control of the action of the mutant genes on eye development involves a group of compounds characteristically associated with nervous tissue. Eye development in the eyK strain may be influenced by the availability of acetyl CoA, which would be expected to affect acetylcholine biosynthesis. Possible mechanisms of action of the effective dietary treatments are discussed, together with a tentative hypothesis regarding the mode of action of the mutant genes on eye development.

The duration of meiosis and its stages has been estimated in Hordeum vulgare variety Sultan grown at 20·0 °C with continuous illumination. The results are in good agreement with a previous estimate of the duration of meiosis and some of its stages in barley. The duration in barley does not differ greatly from that predicted from the previously calculated regression of DNA amount on meiotic duration in diploid plant species. As in other cereal species, meiosis is comparatively short.

A strain of mice that had ceased to respond to selection for high litter size was inbred with continued selection. Depression of the mean proved the existence of residual genetic variance. Four lines survived the inbreeding, and one reached 20 generations with a mean equal to the original strain, thus disproving overdominance as a major cause of the residual variation. The four selected inbred lines were crossed and a new strain derived from the cross was maintained in parallel with the original strain. The new strain showed an improvement of 1·5 mice per litter over the original strain. Thus selection with inbreeding was able to achieve an advance beyond the limit attained by the original selection.

The hypothesis that the residual variation was due to genes with simple dominance was tested by seeing if it could account for the observations with reasonable values of the relevant parameters. The improvement made by the inbreeding and crossing required the elimination of about 30 recessive genes with effects (homozygote difference) of 0·5 phenotypic standard deviations and gene frequencies of 0·2. Consideration of the mean levels of the selected inbred lines in conjunction with the rate of depression found on inbreeding without selection showed that the selection with inbreeding had eliminated about 75% of the segregating reces-sives. The number of genes contributing to the residual variance was therefore about 40. The additive variance generated by these genes was just consistent with the estimate of zero from the realized heritability. Consideration of the original selection showed that about half the genes could have been still segregating when the response ceased. The hypothesis therefore requires the number of genes in the base population to have been about 80. The number of genes required, though large, does not seem impossible, and the hypothesis of genes with simple dominance can account for all the observations.

Using polarography the uptake of oxygen by intact and homogenized mycelium of a wild-type strain and strains of slow-growing non-perithecial (sgp) mutants was compared. It was found that whilst the oxygen uptake of intact, wild-type mycelium increased on the addition of glucose or succinate as substrate, uptake of oxygen by mutant mycelium increased only when glucose was used as substrate and was unaffected by succinate. When, however, homogenates of mutant mycelium were used oxidation of the succinate occurred. It was concluded that the inability of the mutants to utilize succinate was due to their impaired ability to take up the compound across the hyphal wall and this was confirmed using radioactively labelled substrates. It is tentatively suggested that the abnormal growth of the sgp mutants on glucose medium and their impaired permeability to tricarboxylic acid cycle intermediates may be due to reduced availability of high energy compounds caused by a lesion in their oxidative phos-phorylation system.

The usual systems of assay using techniques of chromosome substitution demonstrated in Drosophila and wheat are not applicable to barley (Hordeum vulgare). Chromosomal material for assay may, however, be substituted from one variety into another by using translocations to mark and restrict crossing over in the chromosomes to be transferred. This paper describes the isolation and assay of lines derived in this way.

Seven substitution lines derived from the donor variety Maris Badger and the recipient variety Mars have been scored for quantitative characters in two field trials.

The results indicate that variation in flowering time and other associated characters is largely determined by genes on chromosome 2 and that chromosome 4 is involved in the control of plant height.

The feasibility of the technique as a method of assaying the contributions of chromosomes to qualitative characters by substitution in a diploid is discussed.

Hairs from two stocks of homozygous waved-2 mice have been examined. The observations do not agree with a previous report, that the waving was due to a decrease in the proportion of guard hairs and an increase in the number of constrictions per hair, but are consistent with the view that it arises from a defect of keratinization.

A technique using microserological equipment is described whereby up to 144 quantitative interrupted bacterial matings may be performed concurrently. The technique is easy to use, accurate and reproducible, and eliminates the need for agar plates. However, it is only suitable for 40–42 °C matings and mating efficiency is approximately threefold lower than in test tubes.

The fi+ (fertility inhibition+) property was originally described in R factors related to F (F-like factors). The original fi− factors, in contrast, were related to the transfer factor of a colicin I factor (I-like factors). We describe here a group of R factors which are fi+ but I-like. It is suggested that all the terms fi+, fi−, F-like and I-like be used in the description of transferable plasmids.

Mutants of Aspergillus nidulans unable to use either the choline moiety or the sulphate moiety of exogenous choline-0-sulphate have been selected. Choline-0-sulphate non-utilizing (csu) mutations have no other apparent pleiotropic effects, but it has not yet been established whether they lead to loss of choline sulphatase (and thus of the ability to utilize endogenously produced choline-0-sulphate) or to loss of a specific transport system for choline-0-sulphate or to loss of both.

The problem of replica plating filamentous fungi such as Coprinus lagopus is overcome by inducing micro-colonies with sodium deoxycholate and using ‘Velcro’, a hooked material, to replace velveteen in the standard replica plating technique. ‘Velcro’ is advantageous in that it has a regular pattern of closely spaced hooks which transfer small inocula from the colonies on the master plate.