The broad host-range non-conjugative IncQ plasmid RSF1010 was mobilised with 100% efficiency in membrane filter matings, both in E. coli K12 and P. aeruginosa PAO, by broad host-range conjugative IncP plasmids. No homology between RSF1010 and an IncP plasmid could be detected. In E. coli, IncIα and IncX plasmids, but not IncF, IncN or IncW plasmids, were also relatively efficient at mobilising RSF1010, while in P. aeruginosa, R91–5 (IncP-10) was highly efficient, but pMG5 (IncP-2) and FP2 (IncP-8) were very inefficient. IncP plasmids also mobilised several plasmids derived from RSF1010 for use as in vectors in in vitro recombination experiments very efficiently, and pSC101 quite efficiently: this reduces the level of biological containment possible with these plasmids.

Mapping quantitative trait loci (QTLs) for binary traits in backcross and F2 populations was investigated using stochastic stimulation. Data were analysed using either linear regression or a generalized linear model. Parameters which were varied in the simulations were the population size (200 and 500), heritability in the backcross or F2 population (0·01, 0·05, 0·10), marker spacing (10 and 20 cM) and the incidence of the trait (0·50, 0·25, 0·10). The methods gave very similar results in terms of estimates of the QTL location and QTL effects and power of QTL detection, and it was concluded that in practice treating the zero-one data as continuous and using standard linear regression was efficient.

Experiments were designed to investigate the effect of homozygous deletions upon the frequency and the average length of heterozygous regions in bacteriophage T4D. A long deletion, rdf41, which covers at least the whole rII region, was found to increase the heterozygosity for r48, while no increase was observed when a short deletion was employed. The long deletion was found to increase the average length of amber-HETs by a length approximately the size of the rII region.

A drastic reduction in average HET length was found in FUDR crosses homozygous for the long deletion rdf41, indicating that the type of HET that does increase in FUDR is very short.

In the cross with no deletion in either parent, premature lysis HETs were found to be much longer than normal lysis HETs. Assuming that redundancy HETs are long compared to heteroduplex HETs this result indicates that redundancy HETs are made earlier in the latent period than heteroduplex HETs. A fluctuation in HET frequencies was found for different markers, especially in FUDR.

About half of all HETs, both in normal crosses and in FUDR crosses, was found to be parental for outside markers.

In non-FUDR crosses, polarized segregation was shown by 12 out of 27 multi-marker HETs after normal lysis and 5 out of 22 multi-marker HETs after premature lysis. In FUDR crosses, 24 out of 77 multi-marker HETs showed polarity.

The allele kr1, conditioning ready crossability between wheat and rye when wheat is the female parent, is at a locus already known to be on chromosome 5B of wheat. This locus was mapped using a telocentric chromosome consisting of the long arm of chromosome 5B. Mapping was carried out by analyses of F2 and testcross progenies. The two experiments gave a mean recombination frequency, between the locus and the centromere, of 11·45 ± 3·0%. The possibility of different recombination frequencies in male and female meiosis is discussed.

Single ascospore cultures from triploids were screened as a potential source of disomic tester stocks for the purpose of genetical mapping of chromosomes in yeast. A high tolerance of aneuploidy was found, and strains disomic for only one chromosome were rare. There was a high occurrence of strains disomic at specific chromosomes and in certain multiple combinations of disomic chromosomes.

Longitudinal microtubules appear in Paramecium tetraurelia when cells are ready to divide (ca. interfission age 0·9). They arise in the longitudinal cortical ridges between kineties and form, in each ridge, an incomplete circlet of 15–18 microtubules, disappearing 10–15 min after separation of the fission products (ca. interfission age 0·03–0·04). Vinblastine, colchicine, colcemid, mercaptoethanol, and cold treatments all result in loss of these microtubules, rounding up of the cells, and some suppression of cell division. The tubules are thought to play a role in cellular elongation, morphogenesis, and separation.

Welshons & Russell (1959) have presented data to show that the XO chromosomal constitution in the mouse is female. This conclusion was based on results of genetical tests with sex-linked markers and on chromosome counts. All XO females were matroclinous, that is, they had inherited their X-chromosome from their mother. Females of this type will arise when non-disjunction occurs in the meiotic divisions of the father and results in spermatozoa without a sex-chromosome. Alternatively, the paternal sex-chromosome may be lost from the fertilized ovum if non-disjunction of sister-chromatids occurs during the first cleavage division. This latter explanation has been urged by Ohno, Kaplan & Kinosita (1959), who found no evidence for non-disjunction of the X-and Y-chromosome in an extensive cytolosical examination of the mouse testis.

Unstable alleles, broken chromosomes and stable mutants have arisen in maize out of infected plants of Barley Striped Mosaic Virus and other viruses. Surprisingly, these same events have appeared out of progenies of these infected plants that themselves do not show any infection. These mutants showing instability have resulted from insertions that are not necessarily related. Two of these insertions (BS1 and TZ86) that have been analysed molecularly have the general characteristics of maize insertions with terminal inverted repeats and host duplication at the terminus of the transposon. In other experiments three of the unstable alleles at the a locus in maize (A locus, chromosome 3, short arm; one of genes for anthocyanin control) that arose in derivative lines of the initially treated plants are responsive to a transposable element, the Uq element. It was determined that the Uq element was not present in this initially treated plant but was present in the untreated female plant. It is proposed that the initial treatment induced events that in turn led to the mobilization of elements and that these events continue to occur in later generations. It seems that genomic events once initiated such as mobility of elements cannot be terminated despite a discontinuation of the treatment (virus) and, like a Frankenstein monster, is not responsive to its maker.

rpoB is the structural gene for the β-subunit of E. coli RNA polymerase. The rpoB-3 allele confers resistance to the antibiotic rifampicin and is unusual in being dominant to the wild-type allele. We used the plasmid pZD23, a derivative of the broad host range conjugative plasmid RP4, to introduce the rpoB-3 allele into a range of bacterial species. Species belonging to the same family as E. coli (Enterobacter aerogenes, Citrobacter freundii, Hafnia alvei møller, Klebsiella pneumoniae, Salmonella typhimurium) expressed rpoB-3 to give a rifampicin resistant phenotype; this demonstrated heterospecific transcription. The transfer of pZD23 to the non-Enterobacteriaceae species Azotobacter vinelandii and Rhizobium leguminosarum did not result in rifampicin resistance. In the former case this was due to non-expression of the rpoB-3 resistance phenotype, in the latter case the dominant resistance phenotype had been lost from pZD23. Heterospecific transcription can be used as a criterion for the investigation of genetic relatedness between bacterial species.

The known limits of the distal imprinting region of mouse Chromosome (Chr) 2 are defined by the breakpoints of the translocations T(2;8)2Wa, (T2Wa), and T(2;16)28H, (T28H), in distal H3, and proximal H4 respectively. We have shown that T2Wa and T(2;4)1Go, (T1Go), which has a breakpoint in central H3 map close to a, non-agouti. Ada, adenosine deaminase, lies very near the proximal boundary and Ra, ragged, maps very close to the distal boundary, and is less than 0-2 cM from wasted, wst. From the current data Ada can be taken as the proximal, and Ra as the distal gene marker of the imprinting region on the linkage map. From consensus maps twenty three other markers, including fourteen genes, lie between Ada and Ra, some of which may be useful in investigations of imprinting. Of the markers included in the study reported here, four, Ada, ls, lethal spotting, Ra and wst lie or probably lie within the region but none display any evidence of imprinting. We suggest that recombination frequency is elevated in distal Chr 2, because in none of the crosses could the most closely linked marker be ordered in relation to the translocation breakpoint due to the high frequency of double crossovers.

A pedigreed control strain was divided into three lines which were maintained genetically distinct over nine generations. Mean coefficients of inbreeding of about 0·1 were attained. Results suggest that discernible genetic drift had occurred in several traits. Separate estimates of genetic variance were obtained from observed variation between and within lines. These estimates differed significantly in the case of only one of the eight traits observed. Observed variation between lines agreed reasonably well with that predicted.

Polygenic variation can be maintained by a balance between mutation and stabilizing selection. When the alleles responsible for variation are rare, many classes of equilibria may be stable. The rate at which drift causes shifts between equilibria is investigated by integrating the gene frequency distribution W̅2NΠ(pq)4Nμ−1. This integral can be found exactly, by numerical integration, or can be approximated by assuming that the full distribution of allele frequencies is approximately Gaussian. These methods are checked against simulations. Over a wide range of population sizes, drift will keep the population near an equilibrium which minimizes the genetic variance and the deviation from the selective optimum. Shifts between equilibria in this class occur at an appreciable rate if the product of population size and selection on each locus is small (Nsα2 < 10). The Gaussian approximation is accurate even when the underlying distribution is strongly skewed. Reproductive isolation evolves as populations shift to new combinations of alleles: however, this process is slow, approaching the neutral rate (≈ μ) in small populations.

Conjugating pairs of syngen 1 exposed to 0·1 M-CaCl2 during the time of macronuclear development often abort the new macronuclei and retain the old macronucleus and its associated phenotypes. The new micro-nucleus is retained, however, so that macro–micro heterocaryons can be constructed. Because the macronucleus is from a sexually mature strain, the heterocaryon is capable of mating immediately, without passing a period of sexual immaturity. Macronuclear abortion may prove a useful short-cut in genetic analysis.

Nine enzyme activity variants of liver/erythrocyte pyruvate kinase have been found amongst laboratory and wild mice. Four of these variants have been shown by biochemical and immunological criteria to be mutations of the structural gene, Pk-1s. These four structural gene mutations, and two regulatory gene mutations, define the gene complex, [Pk-1]. One allele of the structural gene, Pk-1sl, found in the inbred strain C57BL, has an unusual phenotype and affects the expression of pyruvate kinase in the liver but not erythrocyte. A possible mechanism for this tissue-specific structural gene mutation is suggested.