Six hundred and ten gynandromorphs were produced in which an X chromosome loss uncovered the vermilion mutation. The mosaic patterns observed indicate that wild type ocelli are incapable of kynurenine production and that, in addition to the eyes, postembryonic kynurenine producing cells originate from two separate regions of the blastoderm. The positions of these regions on the genetic fate map of Drosophila melanogaster correspond to the embryonic precursors which give rise to the kynurenine producing cells of the larval fat body and Malpighian tubes.

Linkage data for the following markers on chromosome 17 of the house mouse were obtained: centromere (marked by translocation R67), Brachyury (T), tufted (tf), H-2, and thin fur (thf). The markers were found to be arranged in that order in the genetic map and the combined genetic distances between individual markers were found to be as follows: Rb7…T, 4·5 cM; T…tf, 5·8 cM; tf…H-2, 5·0 cM; H-2…thf, 15·1 cM. The localization of the thf locus on the non-centromeric side of the H-2 complex provides an important marker for this arm of chromosome 17. The map distances in the centromeric portion of chromosome 17 changed drastically in the presence of various t factors. These factors strongly reduce the recombination frequency in the T…tf and tf…H-2 intervals and this crossing-over suppression is most likely responsible for the linkage disequilibrium between t and H-2 reported earlier. Recombinants involving a t chromosome but occurring to the right of the H-2 complex do not change the properties of t factors suggesting that all determinants responsible for the t phenotype are located in the chromosomal region between T and tf (H-2).

The pattern of inheritance of the autosomal recessive adrenal lipid depletion (ald) allele among the AKXL recombinant inbred mouse lines, derived from a cross between AKR/J and C57L/J, revealed that the ald locus is located on chromosome 1 near the dipeptidase-1 (Dip-1) locus. The linkage was confirmed in a backcross generation and the gene order ln-Dip-1-ald was established.

The genetic control of resistance to the fungus, Cercosporella herpotrichoides, causing the eyespot disease of wheat was studied using the Chinese Spring (Cappelle-Desprez) chromosome substitution lines and F2 monosomic families of hybrids between Cappelle-Desprez and Mara. Chromosome 7A of Cappelle-Desprez was found to increase resistance to eyespot in both types of test. Chromosomes 2B and 5D of Cappelle-Desprez gave increased resistance compared to their homologues in Mara on an F2 background. When substituted into Chinese Spring neither of these chromosomes appeared to increase resistance. Chromosome 1A of Cappelle-Desprez in a Chinese Spring background increased the level of infection. Dominance was towards resistance and the presence of between-chromosome interaction could be deduced.

Alcohol dehydrogenase activity in Drosophila melanogaster may be considered as a quantitative character, since it shows many features typically associated with such traits. Although strains with the electrophoretically fast phenotype generally have activities greater than those with the slow phenotype, presumably reflecting differences in the nucleotide sequences of the structural alleles, within each electrophoretic class there is considerable variation in activity. The expression of the structural gene, in terms of ADH activity, is to some extent regulated by its genetic background. Strains homozygous for particular structural alleles respond to divergent directional selection for ADH activity. Modifiers have been located to the X, second and third chromosomes.

In view of the exceptional usefulness of Drosophila hydei for the analysis of Y-chromosome activity, a technique has been developed which permits the production of large numbers of males lacking a Y chromosome. It is based on the synthesis of new compound(1) chromosomes which carry sufficient rDNA genes to secure survival in the absence of any Y-chromosomal rDNA. Through non-disjunction in males of suitable stocks, fertile Compound(l) females which lack the Y chromosome, phenotypically distinguishable from their normal sibs, are produced in sufficient number to allow the subsequent breeding of X/O males in gram quantities for biochemical studies.

Improvements in cytotoxic technique allowed a determination to be made of the strain distribution and inheritance of Mph-1, the mouse peritoneal exudate cell alloantigen. Mph-lb, the allele in B10 lines, is inherited as a Mendelian co-dominant gene. In a 3-point backcross using the colour markers pink eye dilution (p) and chinchilla (cch) it was shown to map about 36 units from p in the order p-cch-Mph-l on chromosome 7. An alternative antigen, Mph-1.1, has been identified on strains F/St and I/StDa.

Genetic analysis of seven dominant short tailed mutations independently induced by radiation of male mice showed that six were allelic to T (Brachyury) but not identical to it. Homozygotes for each mutant die at least 2 days earlier than T/T homozygotes; two that were studied histologically are indistinguishable from one another. The development of these abnormal embryos is arrested by seven days of gestation, when cells of embryonic ectoderm cease proliferation and become pycnotic. Endoderm and extra-embryonic ectoderm do not seem to be primarily affected, and survive and grow for at least 2 days more. Serological studies of one of these mutations suggest that it is a deletion. A review is presented of these and other T-like mutations that have been described; from this it appears that five different categories of T-like mutants are discernible.

The relative frequency of retention of two mitochondrial loci, determining resistance to oligomycin (oli1) and erythromycin (ery1), has been analysed in petite (rho(−)) mutants derived from a number of unrelated strains of Saccharomyces cerevisiae. The frequency of retention of one marker relative to the other in spontaneous petites showed marked variation dependent on the strain of origin. The differences between strains in this characteristic were shown to be mitochondrially determined. Further, for individual strains, the relative retention of the markers in petites derived after UV-irradiation varied considerably in several cases from that observed with spontaneous petites. The observations on relative marker retention and the varied effects of UV-irradiation are discussed in terms of possible structural differences in the mitochondrial genomes of the various strains.

Chlorpromazine and several other phenothiazines at sub-bacteriocidal concentrations were found to cure an Escherichia coli F′ lac+ strain of its plasmid efficiently. Curing was most efficient at high pH and in complex medium when 70% or more of the bacteria were plasmid-free after 24 h growth of cultures in the presence of the drug.