Three-point transduction analysis was employed to determine the sequence of four structural and two regulatory methionine genes (metA, B, F, H and metI, J, respectively) on two apparently adjacent transduction fragments in Salmonella typhimurium. These fragments were subsequently orientated with respect to each other and the rest of the linkage map by the analysis of recombinants obtained in conjugation experiments. The following clockwise sequence of genes is proposed: -metJ-metB-metF-argF-thi-purD-metA-metI-metH-. The bearing of these results on the regulation of the metB–F and metA–H clusters is discussed.

According to the classical genetic analysis in Paramecium caudatum by Tsukii & Hiwatashi (1983), the E mating type of each syngen is expressed when the cell bears alleles specific for syngen at the Mt locus. The O mating type is expressed when cells are homozygous for the null allele, mt, at the Mt locus. In such mt/mt cells the O syngen specificity is determined by alleles at two other loci called MA and MB. Inthe study reported here, macronucleoplasmic transplantation technique was used to test the above hypothesis. When macronucleoplasm of type E3 (mating type E of syngen 3) was injected into a macronucleus of type O12 (mating type O of syngen 12), some recipients changed to type E of the donor syngen but some others changed to type E of the recipient syngen. Thus, syngen specificity of donor macronucleoplasm controlling type E was converted into that of the recipients, even though the latter has no gene that controls type E. When this transformant expressing type E of the recipiexnt syngen was re-injected back into E of the other syngen, the expression of the converted mating type in some way continued in the recipient. This suggests that syngen specificity of gene Mt of the donor was changed to that of the recipients by intersyngenic transplantation of macronucleoplasm. We also obtained results suggesting that the gene dosage ratio of Mt to mt or Mt to MA and MB may be important for syngen specific expression of type E.

The structure and function of flagella are genetically determined and single gene mutants – for example, lacking in motility or of abnormal flagellar length – have previously been investigated. When such mutants are crossed with wild-type, temporary dikaryons – prozygotes – are formed with two nuclei and a common cytoplasm. The properties of the four flagella – two originally abnormal – have been observed as a function of time. In wild-type × non-motile mutant crosses, restoration of motility has been observed in a number of cases. If the dikaryons are deflagellated regeneration occurs, together with restoration of motility or of normal length to the previously abnormal pair. Complementation at the cytoplasmic level has been found in paired mutants.

An attempt is described to produce chromosome translocations in Glossina austeni which, it is hoped, might ultimately be used for tsetse fly control. The method consisted of selecting among the progeny of irradiated males for cases of inherited partial sterility. Thirty-four per cent of the testable sons of males which received doses of 5–7 krads showed these properties. In two cases the inheritance was patrilineal which suggests that the Y chromosome was involved. In most of the other cases a segregation among both male and female progeny of the partially sterile and normal types occurred and in these cases it appears that autosomes only were involved. Among males in these stocks the segregation ratio was close to 1:1, but in females there was a deficit of the partially sterile type. This may be partly associated with the fact that a large proportion of totally sterile and in-viable females were produced by these stocks. The proportion of zygotes which died at the embryonic, larval and pupal stages as a result of the action of the partial sterility factors varied between factors of different mutational origin. In view of the pattern of inheritance of these factors and their high frequency of induction it is argued that in all probability they are translocations in the heterozygous state.

A paramecium generally bears on its surface but one immobilization antigen from among the many it may have the potentiality for expressing. By assaying soluble extracts of whole cells, it had been demonstrated previously that animals of the E serotype may possess the cross-reacting G antigen. Now the existence of these secondary antigens—immobilization antigens undetected by in vivo tests—has been extended to include unrelated antigens, e.g. G antigen in animals of C serotype.

The amount of these cryptic immobilization antigens varies from stock to stock; also within a stock cultures harvested at different times may have quite different quantities.

The secondary and primary G antigens appear to be indistinguishable by the criteria of antigenic specificities, immunoelectrophoretic mobilities sedimentation rates and ammonium sulfate solubilities. As to their distribution within the cell, both secondary and primary antigens are located primarily on or within the cilia.

Six isolate lines of long standing, from the Centre's Brown Leghorn flock, were intermated in all possible directions, providing thirty cross and six pure line samples. Half the birds from each line and reciprocal cross were kept in floor pens and the rest caged in an adjacent battery house.

Sexual maturity, survivors' production to 500 days of age, and November through June egg numbers, all showed two main factors contributing to variations in cross performance: (1) a significant association with parental production levels as measured by mid-parent averages, and (2) an additional hybrid gain. For November to June production in pens, this hybrid gain appeared to approach a constant for the cross groups. Additional sources of variation were present in age at sexual maturity.

The 500-day records for the penned hybrids exceeded the line average by 50 eggs. Caged samples did less well and showed an advantage of only 34 eggs. In this location the hybrid gain for individual groups decreased with increases in mid-parent level.

Egg weight varied negatively with egg numbers only in the upper half of the wide egg-size range. The best layers fell at the lower end of the covariant range for egg size.

The importance of improving closed strains may not have been lessened by the expansion of the hybrid side of the poultry industry, for the pattern of relationships of line and cross production in this flock is consistent enough to justify the inference that the best hybrids come from the best-producing parents.

Simple, inexpensive techniques were used to analyse the mtDNA of nine chromosomally distinct populations of Petrogale. Eight of these populations occur in sequence along the Great Dividing Range of eastern Australia; six have been described as species. Diagnostic mtDNA morphs were found throughout the latitudinal ranges of four of the described species. A fifth morph spanned the ranges of two described species and three additional taxa which have been designated chromosome races. These five mtDNA morphs, and others with local distributions, were used to assess interactions between the taxa. Limited introgression was indicated across the chromosomal boundaries of P. penicillata/P. herberti and P. inornata/P. assimilis; atypical mtDNA morphs were found within the P. herberti and P. inornata chromosomal distributions. No introgression was detected between P. herberti and P. inornata, whose distributions are separated by the Fitzroy River. Nor was there evidence of recent contact between P. assimilis, P. herberti and P. purpureicollis, despite the late occupancy of parts of the intervening area by unidentified Petrogale. These data, considered in the light of information obtained from previous studies on chromosomes, allozymes and parasites, have contributed to the decision to consider all the eastern representatives of the lateralis-penicillata group of Petrogale as being specifically distinct from each other.

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.

In Drosophila melanogaster two alleles at the Third chromosome resistance locus (Tcr; 3–39·6) were isolated in a screen of EMS mutagenized third chromosomes for dominant resistance to dietary α-methyl dopa, α-MD, a structural analogue of DOPA. Both alleles of Tcr are recessive lethals exhibiting partial complementation. Almost half (48·3%) of the Tcr40 / Tcr45 heterozygotes die as embryos but some survive past adult eclosion. Both the embryonic lethal phenotype and the adult phenotype suggest that Tcr is involved in cuticle synthesis. Tcr mutants suppress the lethality of partially complementing alleles at the α-MD hypersensitive locus, l(2)amd. The viability of Tcr40 / Tcr45, however, is not increased by the presence of a l(2)amd allele. The possibility that the Tcr and l(2)amd mutations reveal a catecholamine metabolic pathway involved in cuticle structure is discussed.