Haem synthetase activity and co-ordination of α- and β-globin chain synthesis have been investigated in prenatal reticulocytes of congenic FL/4Re +/+ Lvb/Lvb and FL/1 Ref/f Lvb/Lvb, mice, which have a marked hypochromic, microcytic, siderocytic anaemia, with reduced erythrocyte numbers at birth, and also in other stocks bearing the f lesion. Haem synthetase activity in f/f reticulocyte homogenates was similar to that in normal cells but was markedly dependent on protoporphyrin added to the homogenate, while activity in normal cell homogenates was relatively independent of added precursor. In cultured normal prenatal reticulocytes α- and β-globin was synthesized in approximately equal amounts during a 4 h labelling period, but in f/f reticulocytes there was an approximate 50% deficiency in β-globin chain synthesis. This deficiency could be repaired by added haem but not by protoporphyrin. Such a lesion is quantitatively consistent with the observed hypochromia of neonatal f/f erythrocytes. The relationship of this abnormality to effects of the f locus on early erythropoietic precursor cells is discussed.

The age of an allele segregating in a finite population may be defined in two ways. They are (1) the age of a mutant gene that has never reached fixation in the population, and (2) the age including any fixation period in the past. Theoretical expressions for these are derived on the assumption that every mutant is unique.

The generalized transducing phage F116 has been used to prepare lysates from fast- and slow-growing cultures of Pseudomonas aeruginosa strain 1. These lysates have been used to transduce a number of auxotrophic markers to prototrophy and the ratios of the numbers of transductants obtained with each lysate have been determined. Since the markers are those which have been mapped by conjugation in previous studies it has been possible to compare the ratios obtained for each marker with the relative position of the marker on the chromosome map. If the assumption is made that there is only one circular chromosome in P. aeruginosa strain 1 it is possible to suggest a way in which two apparently unlinked segments might be joined together. It is also possible to suggest that the chromosome replicates sequentially in two directions from a fixed origin.

Prophage H90 has been found to undergo a phenomenon similar to zygotic induction, during conjugal transfer from a lysogenic donor to a non-lysogenic recipient.

It has not been possible to demonstrate that the level of infectious centres increases concomitantly with transfer of the prophage. However, the genetic consequence of zygotic induction was observed with regard to decreased recombinant yield of markers distal to the prophage. This latter fact has been exploited in interrupted mating experiments, to locate the prophage at between 5 and 7 min on the Pseudomonas aeruginosa strain PAO map. It was further shown by transduction experiments that the prophage does not appear to be linked to clusters of co-transductional markers at the 5 and 7 min locations.

Pawns are behavioural mutants which show impairment in membrane excitability and are, therefore, devoid of normal avoiding reactions. We obtained 103 lines of Pawns through mutagenesis and screening. Among those that yielded to breeding studies, 59 lines belonged to the pwA complementation group and 38 lines belonged to the pwB group. No other genic loci were found in this extensive analysis. Mutants of the pwA locus showed various degrees of phenotypic leakiness. Based on the pheno- and genotypic differences, we estimated that at least 45 independent mutational events were represented in these 103 Pawn lines.

PAM 26, a radiation-sensitive mutant of Escherichia coli strain B, is described. Its properties are attributable to a mutation in a gene, exrB, which is cotransducible with malB. It differs from uvrA (also malB-linked) derivatives of strain B in being sensitive to 1-methyl-3-nitro-1-nitroso-guanidine and γ-radiation, and in being able to reactivate UV-irradiated phage T3. It differs from exrA (also malB-linked) derivatives of strain B in forming filaments during the course of normal growth as well as after irradiation. When exrB was transduced into a K12 (lon+) strain, filaments did not form spontaneously. Three-point transductions established the order of markers as met A malB exrB. Based on an analysis of the frequency of wild-type recombinants in a reciprocal transduction between exrA and exrB strains, it was inferred that they are not isogenic and that the order of markers is malB exrA exrB.

Mean chiasma frequencies and the amounts of between-bivalent chiasma variation were computed for pollen mother cells (p.m.c.) and embryo-sac mother cells (e.m.c.) of five distinct inbred rye lines. Despite the considerable differences for both these metrics shown by the different lines, very little variation was seen between p.m.c. and e.m.c. belonging to the same lines. It is concluded that chiasma formation in p.m.c. and e.m.c. of rye is governed and regulated by a single controlling system of genes and that variation in this genetic system is expressed identically in the two sexes.

Gene and genotypic frequencies for a deleterious mutant in mutation selection balance are derived for an infinite population undergoing partial self-fertilization. These provide formulations of mean survival and the mutational load. Obtained also are the average number of mutant genes and affected individuals stemming from a single mutant.

As a concomitant effect on frequencies at a neutral locus the mutational load is distributed disproportionately among the neutral genotypes. For partially recessive mutant genes on the 1, 1-sh, 1-s scale, the effect is to increase the frequency of the heterozygote and to decrease the frequencies of homozygotes at the neutral locus relative to the frequencies expected with complete neutrality. This apparent overdominance at the neutral locus has been shown to be connected with identity disequilibrium rather than linkage disequilibrium. It increases generally as s and h decrease, and as the proportion of self-fertilization and the degree of linkage increase. The apparent overdominance with complete linkage is generally less than double that for free recombination. For partially dominant mutant genes, h ≥ ½, the effects on the frequencies of heterozygote and homozygotes at the neutral locus are reversed.

A method is described for detecting centromere linkage in Saccharomyces cerevisiae using a simple monohybrid for the locus in question. The method utilizes the two-spored asci produced by a normal homothallic diploid and depends upon a selective elimination of specific chromatids during spore formation. The pattern of selective elimination was not detected in a heterothallic strain but was found to be a dominant trait in an inter-strain cross. It was shown that gross chromosome aberrations are probably not responsible for the two-spored asci produced by either the heterothallic or homothallic strains.

A least-squares diallel analysis of the offspring of crosses of seven inbred lines of house mice was performed for the mean widths of the second (M2) and third (M3) mandibular molars. Significant differences among lines, as well as between inbreds and hybrids (positive heterosis) were found for these characters. Estimates of the heritabilities (from general combining ability variances) were high for both teeth as were estimates of maternal effects. Specific combining ability and reciprocal effects were significant only for the M3. Additionally, X-irradiation reduced the mean number of individuals per litter, and thereby indirectly influenced the widths of both molars.

The semi-dominant X-linked gene tabby (Ta) in the mouse, and one of its recessive autosomal mimics, downless (dl) each produces a mutant syndrome that includes absence of hairs on the tail due to failure of tail hair follicle initiation. However, whereas downless tails failed to produce hair follicles in culture on the chick chorioallantoic membrane, which is in keeping with the adult phenotype of both downless and tabby mice, tabby tails produced follicles at about 40% of the control level. Furthermore, in contrast to previous findings for downless, the culture of mixed genotype epidermis-dermis combinations provided no evidence of a primary epidermal effect in tabby.

Pseudomonas arvilla mt-2 (ATCC 23073) has been shown to harbour a transmissible plasmid which codes for the degradation of benzoate and m-toluate. Plasmid-borne genetic information codes for the conversion of these compounds to catechol then the assimilation of catechol via the meta cleavage pathway.

A new method for obtaining mitochondrial mutants of Paramecium aurelia is described. Sensitive organisms were first placed in medium containing a low concentration (0·02 mg/ml) of erythromycin (ERY), insufficient to prevent fission. The paramecia were then transferred through a graded series of increasing ERY concentrations, with a period of growth at each concentration. A high yield of ERY-resistant mutants was obtained.

Continuous growth in 0·02 mg/ml ERY also resulted in the accumulation of a spectrum of mutants resistant to various concentrations of ERY. Many of these mutants are also resistant to mikamycin. On returning the resistant paramecia to media lacking ERY, some clones remained resistant whilst others reverted to sensitivity.