The fi+ (fertility inhibition+) property was originally described in R factors related to F (F-like factors). The original fi− factors, in contrast, were related to the transfer factor of a colicin I factor (I-like factors). We describe here a group of R factors which are fi+ but I-like. It is suggested that all the terms fi+, fi−, F-like and I-like be used in the description of transferable plasmids.

A temporal survey of the alcohol dehydrogenase locus in a natural population of Drosophila melanogaster from the Canary Islands has revealed the existence of an electrophoretic Fast thermostable variant, mapped within 0.8 units of the structural Adh locus, and which persists over a 6-year period with a frequency ranging from 0.8 to 0.5%.

The gene(s) controlling the high-molecular-weight glutelin subunits in rye (designated as Glu-Rl) was mapped with respect to the centromere using a 1RL-1DS wheat-rye translocation line and sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE). Analysis of 479 seeds from test-crosses between a 1R/1RL-1DS heterozygote and the cultivar India 115, revealed 14·6% aneuploid and 3·95% recombinant progeny. Excluding the aneuploids, this locus was calculated to be 4·65 ± 1·04 cM from the centromere on the long arm of chromosome 1R, which is comparable to the position of the homoeologous loci in wheat and barley.

Trimethoprim-resistant mutants of E. coli K12 have been isolated by-serial subculture in progressively higher concentrations of trimethoprim. High-level resistance depends on the accumulation of several mutational changes. Transduction with bacteriophage P1 has shown that all the mutations involved in resistance are associated with a locus, to be called tmr, between pyr A and pdxA and closely linked to pdxA. Resistance is accompanied by, and presumably due to, an increased activity of the target enzyme, dihydrofolate reductase. The tmr locus may include the structural gene for dihydrofolate reductase but the only mutations that have so far been observed are concerned with regulation.

Population cages were set up containing an X-chromosome balancer, and either a single wild-type chromosome(homozygous cages) or a mixture of wild-type chromosomes(heterozygous cages). The balancer chromosome was eliminated more rapidly from the heterozygous cages, indicating that chromosome heterozygotes are at an advantage over chromosome homozygotes. The disadvantage of X-chromosome homozygosity in the female is estimated to be about 40%. From earlier studies it is known that the average disadvantage of homozygosity for either of the two major autosomes of D. melanogaster is approximately 80%. Since these autosomes are both about twice as long as the X chromosome, the disadvantage per unit length is similar for both chromosomal types.

Both X-chromosomal and autosomal heterosis can be explained by either dominance or overdominance at individual loci. However, a dominance model can only explain the similarity if many of the X-linked loci (about 50%) are limited in expression to the female.

Chromosome 1 with one or two long insertions has been previously found in natural mouse populations. The inheritance of chromosome 1 with two insertions from the Yakutsk population is analysed in this paper. It was demonstrated that heterozygous females transmit this chromosome to 80–85% of offspring. The observations made at M II, in conjunction with the recombination data, allowed us to conclude that preferential passage of the chromosome 1 with insertions to the oocyte and egg, rather than to the first and second polar bodies at meiosis, is the causative factor of the distorted segregation. A meiotic drive of such potency has not been previously reported for female mammals. The possible mechanism of the drive is discussed.

The expectation for a gene dose effect in an X-linked phenotype is that the corresponding metrical trait in heterozygous females will lie between values for affected hemizygous males and unaffected males and females. We made sequential measurements (at 30, 60, 90, 120 and 150 days) of serum phosphate concentration and tail length in mice with X-linked hypophosphatemia (genotypes: Hyp/Y, Hyp/+ and Hyp/Hyp) and in their normal litter-mates (genotypes: +/Y, +/+). We also measured renal mitochondrial 25-hydroxyvitamin D3-24-hydroxylase (24-hydroxylase) activity in 5 to 7-month-old mice fed control and low phosphate diets and representing all five genotypes. The animals were obtained by controlled breeding under uniform environmental conditions. The mutant animals all had uniformly and significantly lower serum phosphate levels, shorter tail length and higher 24-hydroxylase activity relative to unaffected litter-mates. There was no evidence of a gene dose effect because values were not significantly different among the three mutant genotypes. We also studied the influence of gamete of origin on serum phosphate, tail length and renal mitochondrial 24-hydroxylase activity in the Hyp/+ offspring of affected males (Hyp/Y) or affected females (Hyp/+ or Hyp/Hyp). We found no effect on the distribution of trait values. We conclude that parental origin of mutant allele does not explain the absence of a gene dose effect in Hyp mice.

Advantage was taken of a unique situation to test, with adequate controls, the assertion that male and female gametes conjugate at random. The data concern the aberrant locus T of the mouse, at which there are a number of t alleles that enter into the majority of effective spermatozoa of males heterozygous for one of them. Segregation in females is normal. Evidence is presented for one of these t alleles, tailless-Edinburgh (te), that conjugation between gametes was not at random when this gene was present in spermatozoa. When a choice of eggs was presented by heterozygous females, tailless-Edinburgh spermatozoa united more frequently with normal than with brachyury eggs and more frequently with brachyury than with tailless-Edinburgh eggs. The relevance of this finding is discussed in relation to expected equilibria of t alleles in closed populations. Other forms of selective fertilization are discussed and their genetic consequences compared.

Mutant colonies of yeast are described which varied in colour from blue to green and in intensity of colour when grown on medium containing methylene blue. Blue mutant colonies contained more dead cells, decolorized redox dyes more slowly, had a higher respiratory quotient on glucose containing medium, and absorbed more methylene blue dye than did wild-type. The blue colony phenotype was induced both spontaneously and at high frequency by ultraviolet light and ethylmethane-sulphonate in both haploid and diploid strains. Many of the light-coloured colonies isolated following mutagenic treatment reverted to wild-type when subcultured but most dark-coloured colonies remained stable. Stable blue mutants were shown to arise by mutation of many separate nuclear genes in haploids and were often caused by recessive lethals in diploids.

Grizzled (gr) is a recessive gene with complete penetrance but reduced viability. It is linked with waltzer (v) in linkage group X, the recombination frequency being 14·6 ± 2·6%. Its visible effect is to dilute the yellow pigment of the hairs. Body weight is reduced by about 25% atbirth and remains at about 10–20% below that of non-grizzled litter mates. Viability up to the time of classification is about 50–60% of that of non-grizzled litter mates. The mortality of grizzled homo-zygotes occurs at all stages from about 10 days of gestation up to the time of classification. No specific cause of the mortality was evident.

During meiosis the two parts of a tandem duplication are able to pair in a double loop instead of pairing with the corresponding region of the homologous chromosome. The frequency of intrachromosomal exchange within this double loop was measured in heterozygous females of tandem duplication Dp(1; 1)Gr by the phenotypes of the exceptional F1 males. The intrachromosomal exchange frequency is increased significantly by both the ‘interchromosomal effect’ of heterozygous inversions in the autosomes and by a double inversion in the homologous X chromosome. Distribution of the exchange events depends on the pairing situation and its frequency within the double loop. The analysis of clusters of intrachromosomal recombinants observed favours the assumption that this exchange type is exclusively a meiotic event.

Oral morphogenesis in stock 51 of Paramecium tetraurelia was investigated using the techniques of Chatton-Lwoff and protargol silver impregnation. During the stomatogenesis accompanying divisional morphogenesis a new oral anlage field and endoral kinety are formed and persist throughout the interfission period in both the proter and the opisthe. This previously overlooked fact is important for understanding the developmental origins and significance of the endoral kinety and the oral anlage field. Previously, the kinetosomes constituting the oral anlage field were thought to be formed just prior to the onset of stomatogenesis, being in some way derived from the kinetosomes of the endoral kinety. The demonstration of a permanent anlage field as an integral component of the oral assemblage suggests that the earliest stages of stomatogenesis might best be viewed as temporally controlled surfacing and/or ciliation of pre-existing kinetosomes rather than their de novo synthesis. The endoral kinety would thus have no contributory role in the formation of the anlage field used in the immediately ensuing stomatogenesis.

In many reptiles, sex determination is temperature-sensitive. This phenomenon has been shown to take place in the laboratory as well as in nature, but its effect on natural populations remains questionable. In the turtle Emys orbicularis, the effects of temperature override a weak mechanism of genetic sex determination which is revealed in incubation at pivotal temperature. At this temperature, the sexual phenotype is concordant with the expression of the serologically defined H-Y antigen (H-Ys) in non-gonadal tissues; males are H-Ys negative (H-Y−) whereas females are H-Ys positive (H-Y+). To estimate the importance of sexual inversion (sexual phenotype and H-Ys expression discordant) in populations of Brenne (France), the frequencies of male and female sexual phenotypes among H-Ys phenotypes were determined. The frequencies of sex reversed individuals are low, only 6 % of phenotypic females being H-Y− and 11 % of phenotypic males being H-Y+. According to these data, two theoretical models have been constructed to estimate the contribution to sex determination of individuals in relation to their genotype. The first model excludes any influence of incubation temperature and sexual phenotype on the fitness of individuals. The second one considers that these parameters influence fitness because this model has been previously shown to favour environmental sex determination. In both models, it appears that sex determination can be viewed as genotypic and monogenic with some individuals sexually inverted by theaction of temperature. One category of homozygous animals differentiates mainly into one sex, and the heterozygous animals differentiate mainly into the other sex. The second category of homozygotes has a low frequency in the populations and can differentiate as male or female without high constraint. Then it is estimated that in Brenne approximately 83% of the eggs are incubated in conditions allowing the genetic component to influence sex determination.

Measurements of chiasma frequency over a range of temperatures from 9 to 35 °C in euploid wheat and lines nullisomic for chromosome 5D showed the absence of chromosome 5D greatly to increase the sensitivity of chiasma frequency to temperature, resulting in complete univalence at the lowest temperatures. Careful examination of meiotic prophase showed the lowering of chiasma frequency to be correlated with failure of zygotene chromosome pairing, justifying the use of the term asynaptic. Observation of the pairing behaviour of an isochromosome in the nullisomic 5D background suggested that the asynapsis was due to a failure in the mechanism of chromosome pairing rather than of the pre-alignment of homologues. The observed effects in the absence of chromosome 5D could be due to the presence of a recessive allele at the locus of chromosome 5A, also known to control stability of chiasma frequency to temperature. In conclusion it is pointed out that in euploid wheat the sensitivity of chiasma frequency to temperatures within the normal meteorological range could influence the cytological stability of the wheat crop.