Two alleles of a gene (rac) unlinked to the mating-type locus (mt) have been identified in strains of Physarum polycephalum from different laboratories. Heterothallic strains differing in mt alleles cross more rapidly if they differ also in their rac alleles. The recovery of hybrid plasmodia from crosses between apogamic (mth) and heterothallic strains is more likely to be achieved if strains of different rac genotype are used.

The previously isolated plasmid pND3, arising from recombination between the TOL catabolic plasmid and the R plasmid R91, was transduced by pf16 in Pseudomonas putida. Apparent transductional shortening was evident in 25% of the transduced pND3 plasmids. Transductants were isolated which had segregated the antibiotic resistance marker, transfer ability and some of the catabolic functions of the parent plasmid.

A combined cytological and genetic analysis has been carried out to determine whether the spontaneous male recombination associated with a line of Drosophila melanogaster derived from Southern Greece (31.1 MRF) involves chromosome breakage and random reunion. In all crosses showing male recombination, extensive abnormalities involving anaphase bridges and fragments were found at first and second meiotic divisions. This confirms that the low level of recombination associated with male recombination lines is not produced by normal, controlled crossing-over of the type found in females, but by chance reunions, following more erratic breakage events at first and second anaphase. In addition the occurrence of some limited premeiotic recombination cannot be excluded. The 31.1 MRF system shows higher recombination levels at elevated temperatures (29 °C) and chromosome abnormality frequency is also greatly increased. The 31.1 MRF induces both male recombination and chromosomal abnormalities at meiosis when it is inherited from females deriving their cytoplasm from stock other than CyL4/Pm. It is concluded that this factor acts independently of sex and that the reciprocal cross effect is caused by a cytoplasmic factor which the 31.1/CyL4 strain inherited from the CyL4/Pm stock.

Cell numbers in four organs of large, control and small mice were estimated by nuclear counts. Average cell mass was estimated from the cell number and the organ weight. The mice were from the selected Q-strain with six replicate lines in each size-group. The organs were lung, liver, spleen and kidney. At 6 weeks of age the large mice had more cells and larger cells than the controls in all organs; the small mice had fewer and smaller cells than the controls. The regression of log cell-number on log-organ weight provides a measure of how much, proportionately, cell number contributes to the differences in organ weight. In the lung and spleen, cell number contributed about 70% of the strain differences in organ weight, cell mass contributing about 30%; in the liver and kidney the relative contributions were about equal, at 50%.

Cell counts at different ages from 3 to 15 weeks showed that cell number and cell mass contributed to the increases of organ weights during growth in roughly the same proportions as stated above. From this it is concluded that the main effect of selection for body weight has been to speed up or slow down the normal processes of cellular growth.

A study of inbred strains of the mouse using competitive protein-binding techniques revealed significant strain variation in the total plasma thyroxine levels and in the plasma-free thyroxine index. Measurements of minimal metabolic rates also showed strain variation, but the positive correlation which might be expected between the plasma-free thyroxine index and the minimal metabolic rate did not obtain. Possible explanations are discussed.

D. melanogaster imagoes were collected weekly throughout the summer and early fall of 1976. Their Adh genotypes were determined by electrophoresis. The frequency of the Adh4 isoallele fluctuated throughout the period of study. Correlation coefficients assuming no delay, one week delay, two weeks' delay, three weeks' delay, and a four-week delay of the effect of temperature on the frequency of the Adh4 isoallele were insignificant. It was concluded that temperature alone may not be a selective factor but may be selective in combination with other environmental factors.

Curing of an F-prime plasmid by imipramine was most efficient on bacteria growing semianaerobically at 37 °C. The plasmid curing effect of imipramine was increased in the presence of methylene blue, whilst fluorescein, chlorpromazine-sulphoxide and tetraoxyanthrachinon antagonized the plasmid curing action of the drug. In addition to its plasmid curing effect, imipramine treatment selected for Lon mutants at high frequency. Lon mutants show increased resistance to the drug but cured strains, if Lon+, are not resistant.

Incidence of colourblindness among 3325 males belonging to 21 endogamous Dhangar castes (shepherds) of Maharashtra, India, has been reported. Of the 21 castes studied 5 lacked the gene for colourblindness, while in other groups it varied from 1% to 55%, with a series average of 2·65%. The low incidence of observed colourblindness has been discussed in the light of the nomadic way of the life of some of the Dhangar castes. The results have been compared with other nomadic populations of Maharashtra. The results, in general, are compatible with the Post and Pickford's hypothesis of differential selection for colourblindness.