Mitochondrial malic enzyme (MOD-2) was found to be missing in partially complementing genotypes between lethal deletion alleles at the albino locus in Chromosome 7 of the mouse. Since such partial complementers survive to adulthood, the absence of normal mitochondrial malic enzyme is compatible with life; however, the sterility of both females and males may be correlated with this enzyme deficiency. Of the six radiation-induced lethal albino mutations, five includedeletions for the Mod-2 locus mapping 1 centimorgan distally from c. Our data indicate that the maximum genetic distance occupied by any of these deletions is 6 centimorgans.

The sex specific bacteriophage PR4 has been found to plate on P. aeruginosa strains harbouring the TOL catabolic plasmid or the plasmid pND2 derived from TOL. Based on this, attempts were made to place TOL into a Pseudomonas plasmid incompatibility group and by showing that pND2 is incompatible with the R plasmid R2, TOL has been placed into the P-9 group. The NAH catabolic plasmid has been reported to be incompatible with TOL, pND2 and a variety of other plasmids derived from TOL. Thus, these plasmids also would appear to belong to the P-9 incompatibility group.

A genetic analysis was made of the Female-lethal (Fl) locus of Drosophila melanogaster. This is an X-linked mutation which causes lethality only in females. Other alleles do not complement Fl and are either lethal or sterile when homozygous in females. Complementation studies on Fl alleles demonstrate that there is no simple ranking of these alleles in terms of severity of phenotypic effect. Dosage manipulation of Fl alleles indicates that the sex-specificity is not a consequence of gene dosage effects. Viability studies on males carrying Fl alleles show that Fl alleles have no effect on viability regardless of the presence or absence of a Y chromosome. The Fl locus is therefore sex-specific. The hypothesis that Fl+ is involved in the establishment of imaginal phenotypic sex cannot be substantiated on the basis of experiments utilizing sex-change mutations.

A quite specific kind of sterile F1 female, called SF females, arises only when females of strains denoted reactive are crossed with males of the other class (inducer). It was previously shown that this sterility results from a nucleocytoplasmic interaction between the maternal reactive cytoplasm and a factor, called I, which may be born by any one of the paternal chromosomes. In SF females, but not in their brothers, a varying proportion of reactive chromosomes are able to acquire irreversibly the I factor, independently of any classical genetic recombination with the inducer chromosome(s). During this process, called chromosomal contamination, the contaminating chromosome(s) do not undergo any apparent change. The present paper deals with the efficiency of both original inducer and contaminated chromosomes to yield a more or less intense SF sterility. The Otanu inducer laboratory strain contains at least two types of X chromosomes (called strong and weak) which differ genetically with respect to their inducer efficiency. Reactive third chromosomes were contaminated by these strong or weak X chromosomes and their inducer efficiencies compared. Results show that they are on average stronger when they have been contaminated by strong X chromosomes than when contaminated by weak ones. Such a correlation favours the hypothesis that chromosomal contamination is due to the insertion of some genetic element(s) into reactive chromosomes.

The origin of triploid (3N) 5½-day blastocysts in rabbits is inferred from the segregation of sex chromosomes and of an autosomal M-marker whose properties are described. 39 triploids and no tetraploids were scored among 1454 chromosomally scored blastocysts. A delay of 8 h between an ovulatory injection and subsequent insemination raised the estimated normal incidence of 0·59% triploid blastocysts to 3·13%. The increase is ascribed primarily to digyny (17 blastocysts), and to diandry probably mediated by dispermy (1 blastocyst). The triploid components of the two 2N/3N mosaics and the one 3N/6N were digynic. Neither superovulation nor insemination of excessive numbers of spermatozoa could be shown to give rise to triploid embryos. The diandric triploid was X Y Y, the first of this constitution apparently reported in the rabbit. There was some evidence that X X Y triploid blastocysts up to 5½-day gestation are more viable than X X X. In the 2N/3N mosaics each component had been entered by one spermatozoon, and the dliploid component could not have been merely a contamination by dliploid maternal somatic cells. In 2N/4N, 2N/4N/8N and 3N/6N mosaics, each polyploid component showed an exact doubling of the marker chromosome constitution of a component of lower ploidy; their origin is ascribed to doubling or redoubling of chromosome number in isolated embryonic cells. With earlier data included, 49·08 (± s.e. 1·96)% of 652 diploid blastocysts were X Y. 460 non-experimental weaned rabbits were all cliploid.

Linkage disequilibria between pairs of 8 polymorphic enzyme loci (αGpdh, Mdh, Adh, Est-6, Pgm, Odh, Est-C and Acph) in some 100 natural population samples of Drosophila melanogaster were examined. The estimates of linkage disequilibrium were made from zygotic frequencies. The magnitude of linkage disequilibria are small and similar to those in previous reports. Variation in linkage disequilibrium among related subpopulations was analysed by analysis of variance of the correlation coefficients. Despite the small absolute value of linkage disequilibrium there is a suggestion of a correlation among related subpopulations. The magnitude of linkage disequilibrium was observed to be positively correlated with linkage. Two cage populations were observed to demonstrate large amounts of linkage disequilibrium between closely linked loci in contrast to the situation in natural populations. This is attributable to the finite sizes of these cage populations.

The ‘maxy’ technique was used for scoring the frequencies of whole body and fractional mutations in the progeny of males of Drosophila melanogaster that had been irradiated with 2000 R, irradiation being followed or preceded by treatment with caffeine or acriflavine. Three 2-day broods were used, and males irradiated without subsidiary chemical treatment were used as controls. Both chemicals whether given as post- or pre-treatment strongly reduced the frequencies of fractional mutants in all broods. The frequency of whole-body mutants was unaffected in the first two broods and suffered a moderate reduction in the third. These results are discussed in relation to the hypothesis that repair processes regulate the development of a primary lesion into either a whole-body or a fractional mutant and that the functioning of the repair enzymes depends on the state of maturity of the male germ cell.

The question of Drosophila laterality has been investigated in two species and in several strains by attempting to modify degrees of laterality (wing folding and directional choices in mazes) via selection and by ascertaining individual courtship behaviour preferences (circling, foreleg tapping, and wing extending). The results of courtship studies in D. paulistorum strains and in D. melanogaster indicate that, although individual members of a strain may be entirely right or left dominant, the majority of individuals are ambidextrous. As a group, there was no preference for right or left behaviours, and laterality was not a factor in success of courtship. The absence of lateral preference in courtship is consistent with the failure to demonstrate any genetic component for D. melanogaster left and right wing folding and maze behaviours.

Experiments were carried out to see if rare male mating advantage could be detected when males differ at only one locus. The eye colour mutant sepia was inserted into a strain of Drosophila melanogaster homozygous for a first, second, and third chromosome from the Canton-S strain. Tests for the rare male advantage were conducted using ratios of 4:1, 1:1, and 1:4 of the coisogenic wild-type and sepia males. No deviations from expected types of matings were observed. The results are discussed with respect to possible conditions necessary for the rare male effect to occur.

The sterility which is associated with male recombination induced by 31.1 MRF was studied genetically and cytologically. In all crosses it was found that female sterility mainly involves failure of the heterozygous females to lay eggs because their ovaries are atrophic. Under the optical microscope, the atrophic ovaries were seen to contain only germaria in their ovarioles. It was also found that in some cases 31.1 MRF affects only one of the two ovaries of the same female. This observation suggests that defective development of atrophic ovaries is not due to influences from the rest of the body but should be attributed to the inability of the germ cells to differentiate. Moreover, various stocks as well as homologous chromosomes were found to react differently to 31.1 MRF with respect to female sterility. In their effect on male sterility it was observed that some strains behave as neutral and others as reactive when mated with 31.1/Cy L4 males.

Preliminary investigation of the genetic basis of diapause in the gypsy moth, Lymantria dispar, involved a comparison of reciprocal crosses between wild-type moths and a selectively bred ‘non-diapause’ strain with the parental stocks, where half of the eggs resulting from each of the four mating types were exposed to one month of chill at 5 °C. The presence of chill dramatically altered the phenotypic expression of diapause-dependent characteristics. Early hatching was completely recessive in unchilled eggs, while hatching time was intermediate in chilled eggs, and there was no difference between reciprocal hybrids. Proportion of eggs hatching and, therefore, number of larvae produced was also influenced by chill. Unchilled hybrids did not differ substantially from wild-type eggs, while chilled hybrids were closer to the performance of the selected line. In this case, a significant reciprocal difference indicated some involvement of sex-linkage in the inheritance of diapause.

Initial experiments demonstrated that the plasmid R6K cannot be transferred to or maintained readily in the E. coli DNA polymerase I deficient strain JG138 polA1. Results with E. coli MM386 polA12 (R6K), which has a temperature sensitive polymerase I enzyme, showed cell division becomes abnormal when the polymerase I enzyme of the host bacteria is inactivated at the restrictive temperature. Under conditions of polymerase I deficiency, R6K replication, as measured by monitoring R-factor-mediated β-lactamase activity, also becomes abnormal with the loss of multiple R6K copies per cell and the apparent maintenance of a single R-factor copy per cell.

Evidence is presented that a strain of Pseudomonas putida harbours a catabolic plasmid which encodes for the degradation of p-cresol through the protocatechuate ortho cleavage pathway. This plasmid can transfer giving approximately 10−3 transconjugants per donor cell, can be cured with mitomycin C, belongs to the P-9 plasmid incompatibility group and can be transduced with the bacteriophage pf16.

An inherited exencephaly in the mouse is described, using embryos at 11–17 days gestation. The cephalic portion of the neural tube remains open on the dorsal surface, the bony vault of the brain fails to develop, and the tissues of the brain are exposed; the development of these tissues, which is somewhat variable, is described. There is strong evidence that the condition is due to a single recessive gene, xn, with full viability until birth. Penetrance is twice as high in females as in males, and it varies overall according to the genetic milieu studied, from 33% to 84%. These features, and the absence of pleiotropic effects and of genetic evidence of associated chromosomal anomalies, make its inheritance different from that of exencephalies so far described.

We have examined karyotypes of five species from five genera of cyprinid fishes endemic to the central and southeastern United States: Campostoma anomalum, Hybognathus hayi, Hybopsis aestivalis, Phenacobius mirabilis, and Pimephales vigilax. All five have a diploid chromosome number of 50. Variation in chromosome arm number among the five species is slight, and may be due to measurement error or technique difficulties. The karyotypes of 40 North American cyprinids are now known. All but five species have 50 (diploid) chromosomes. Variation in chromosome arm number also appears minimal; one-armed chromosomes (centromeres subterminal to terminal) normally comprise only a small fraction of the karyotype, and each species has roughly the same number of chromosomes with median and submedian centromeres. The conservatism of gross chromosomal evolution among these fishes is not in accord with recent hypotheses which suggest that progressive evolution of organisms may depend to a large degree on gene rearrangement brought about by gross chromosomal restructuring. Cyprinids are a highly speciose group in North America, and there is relatively strong morphological differentiation among species. The present data suggest that gross chromosomal restructuring may play only a minor role in the speciation and evolution of these fishes.

The multi-locus systems expressing non-epistatic and generalized symmetric selection lend themselves to the study of the stability of certain central polymorphic equilibria. These equilibria persist when any form of migration connects demes which share a common equilibrium. The analysis of the stability of the equilibrium in the global system is tractable, thus supplementing known protection results for two alleles at one locus with stability conditions on an internal equilibrium involving an arbitrary number of loci, each with an arbitrary number of alleles. Two of the principal findings are that stability of central Hardy–Weinberg type equilibria increase with ‘more’ migration and ‘more’ recombination. As a corollary, local stability in each deme implies stability in a system with migration superimposed; but instability in each deme when isolated does not imply instability when migration is superimposed.

The allozyme polymorphism of Diadromus pulchellus has been analysed at 22 loci, the expression of one (Est-4) being male-limited. Six loci were found polymorphic for two (Ldh-1, Ldh-2, Acp-2, Pgi and Sdh) or three (Est-3) codominant alleles. Allele frequencies are similar in males and females at four loci in a laboratory population but there are important heterozygote deficiencies in females at three of them. The possibilities of negative heterosis or assortative mating to explain this deficiency are discussed.

Mutations in the rex gene of phage λ affect lysogeny. λrex− phages have an increased probability of forming abortive lysogens instead of stable lysogens. In addition, established lysogens produce elevated levels of cured cells during anaerobic but not aerobic growth. It is suggested that the function of the rex gene is related to excision or repressor function.

The method of heritability estimation proposed by Abplanalp (‘linear heritability’ estimation) is reviewed and the formulation simplified. It is equivalent to the regression of performance of sibs of an individual, itself excluded, on that of the individual. The method is found to be slightly biased in small samples but, in terms of sampling variance, can make efficient use of the data.

Experiments were carried out to investigate genetic relationships within a population of Coriolus versicolor (a polyporaceous basidiomyceto causing white rot of wood) present in a birch stump. The population consisted of individual dikaryons occupying longitudinally continuous columns of decay separated from one another by narrow, dark, relatively undecayed interaction zones. These dikaryons were shown to be genetically homogeneous throughout their respective decay columns by dedikaryotization procedures. They were mutually antagonistic when paired in culture, but monokaryons derived from their fruit-bodies were interfertile. Experiments using synthesized dikaryons indicated that antagonism is inevitable between genetically distinct mycelia, but that the intensity of interaction diminishes with increased relatedness. Results of pairings between synthesized dikaryons and monokaryons varied according to the relatedness of the isolates. Antagonism invariably occurred when the monokaryon contained a nucleus differing from both nuclei in the dikaryon, but this did not necessarily prevent dikaryotization. Often in this situation dikaryotized sectors developed in the monokaryon visibly separated by zones of antagonism (‘tracks’). Where the monokaryon contained the same nucleus as one of the components of the dikaryon, antagonism usually occurred initially, but normally the colonies eventually fused.