An innovative approach to tree breeding called ‘breeding without breeding’ (BWB) is presented. The method, as applied on the material in hand, allows the capture of 75–85% of the genetic response to selection attained through conventional programmes without the need to do any controlled pollination and simplified or possibly no experimental field testing: both considered to be the most resource-demanding activities in breeding programmes. BWB combines the use of genotypic or phenotypic pre-selection of superior individuals, informative DNA markers for fingerprinting and pedigree reconstruction of offspring to assemble naturally created full- and half-sib families resulting from mating among selected parents, and quantitative genetics analyses to identify elite genotypes for further genetic improvement or the establishment of production populations. BWB utility is demonstrated using a retrospective study of Douglas-fir (Pseudotsuga menziesii) progeny tests consisting of offspring produced from 150 controlled crosses among 60 parents and established over three sites. The empirical results are supported by theoretical expectations demonstrating anticipated minimum genetic response compared with conventional approaches. The method's simplicity offers an exceptional opportunity for the development of comparable breeding efforts in developing countries, advanced and new breeding programmes, and economically important and ‘minor’ species.

The Rec-1 strain of Caenorhabditis elegans increases recombination frequency three-fold. In this paper, we have investigated the effect of Rec-1 on the intragenic recombination phenomena of crossing-over and gene conversion. These events were increased two- to three-fold as was X-chromosome non-disjunction. All of the recovered recombinants were independent events, indicating that Rec-1 does not act pre-meiotically. The pattern of recombination in the Rec-1 strain resembles a meiotic pattern more than a radiation expansion. We conclude from this result that the Rec-1 enhancement of recombination is not the result of an increased number of DNA lesions randomly distributed along the chromosome. The increased recombination frequency of Rec-1 was not accompanied by any detrimental effects on growth, progeny number or spontaneous mutation rate. In this regard, the results may have implications for models which propose either selective advantage or disadvantage accompanying increased recombination.

Mi-spotted (misp) is a new mutation in the mouse at the microphthalmia (mi) locus. It has no obvious visible effect in either the heterozygote (misp/+) or homozygote (misp/misp) and was discovered by virtue of its interaction with white (miwh). Mice of genotype miwh/misp are pale yellow with white spots; yellow areas later become ‘sooty’ at the first moult.

Though mice of genotypes a/a; misp/+ and a/a; misp/misp cannot be visibly distinguished from those of a/a; +/+, the amount of tyrosine-2-C14 incorporated in melanin in skins of 5-day-old mice of these genotypes differed. Assays of tyrosine incorporation were extended to include other non-agouti genotypes differing only at the microphthalmia locus. The amount of tyrosine incorporated was greatest in +/+ followed in order by misp/+, misp/+, misp/misp, miwh/+, miwh/misp, and miwh/miwh.

Pigment granules were examined in club hairs of these same genotypes for different regions of the hair shaft. Hairs of misp/+, misp/misp, and mi/+ could not be distinguished from +/+ either in number, kind or arrangement of granules. Hairs of miwh/+ showed reduced cortical and medullary pigment, especially distally, which was even more pronounced in hairs of miwh/misp. Medullary granules of miwh/misp varied greatly in size with a few large yellow-brown granules.

Aggregation chimaeras were made from embryos of C57BL/6 and BALB/c mice. Chimaeric and control females were mated with ICR males at 8 weeks of age and their litter sizes were evaluated over a 5-month period after the first mating. Progeny tests showed that 18 of 27 chimaeras produced oocytes of both genotypes. The mean litter sizes of C57BL/6, BALB/c and their F1 crosses (C57BL/6 × BALB/c and BALB/c × C57BL/6) were 8·14, 9·36, 13·38 and 13·40, respectively. The mean for chimaeras was 11·54 and chimaeric heterosis was evident, but it was not as much as heterosis in the F1 When the chimaeras were classified into the mixed and single-genotype progeny chimaeras, chimaeric heterosis was observed only in the mixed-progeny chimaeras. Quantitative GPI analyses in ten organs showed that the degree of chimaerism in the mixed-genotype progeny chimaeras was higher than that in most of the single-genotype progeny chimaeras and that the degree of chimaerism in the ovaries was positively correlated with litter size in the mixed-genotype progeny chimaeras. On the other hand, such correlation was not observed in the single-genotype progeny chimaeras.

Linkage data, obtained by a combination of selective analysis of haploid recombinants and analysis of segregating heterozygotes, are given for twenty-eight loci in Streptomyces coelicolor A3(2). This brings the total known loci for the organism to thirty-nine. The two linkage groups previously recognized remain separate, and their lengths have been increased to about 60 and 70 recombination units respectively. Whether the two linkage groups correspond to two chromosomes remains an open question.

Three further examples of close linkage of pairs of functionally related loci have been found (a trio of such loci was already known), and three other pairs provide possible examples of the same phenomenon. Some loci which are clustered in Salmonella are unlinked in Streptomyces.

In the fission yeast Schizosaccharomyces pombe, growth responses of mutants strains in the de novo purine synthesis pathway, in the purine interconversion system, and of various double mutants, have been studied upon different purine-supplemented media. The results show that exogenous purine utilization as nucleotide source is based exclusively upon pyrophosphorylation of purine bases, and they make it possible to identify most of the enzymic steps acting, in this organism, upon a purine ring to give another purine ring.

A scheme of the interconversion system in Schizosaccharomyces pombe is given.

Some 400 wild mice (Mus domesticus) from southern Germany (the triangle formed by the cities Tübingen, Heidenheim and Friedrichshafen) were karyotyped and, in 243 of them, the chromosome compositions were determined by banding techniques. Virtually all mice tested carried at least one pair of metacentric chromosomes; some mice had up to ten metacentric chromosomes. Based on their chromosome composition, five mouse populations could be distinguished. Population I was characterized by the diploid chromosome number of 2n = 38 and the presence of two copies of metacentric chromosome Rb(4.12)1Tu. This translocation was also found in virtually all mice captured in southern Germany, almost always in a homozygous state. Mice of other populations had extra metacentric chromosomes Rb(5.15)15Tu (population II), Rb(13.14)17Tu (population III), Rb(5.14)18Tu (population IV) and Rb(11.13)6Tu (population V). In addition, rare variants (1 or 2 mice) were found in the different populations, which were heterozygous for additional metacentric chromosomes. Population V was quite heterogeneous in that it contained up to five metacentric chromosomes in addition to those mentioned. The number and the composition of these metacentric chromosomes varied from place to place. With the exception of population I, the individual populations occupied geographically distinct areas: Representatives of population I were found concentrated in one area, but, in addition, some were scattered over the entire studied region.

1. A two-hour relative deficiency of nicotinamide, produced by maternal treatment with 6-aminonicotinamide, resulted in a maximum frequency of vertebral fusions following treatment on day 9·5 of gestation, and a maximum frequency of cleft palates following treatment on day 13·5.

2. Both defects appeared with higher frequencies in the A/Jax than in the C57BL/6J inbred strain.

3. The frequency of induced vertebral fusions in F1 embryos from crosses between the strains was higher when the father was from the A/Jax strain than when the mother was—a patroclinous reciprocal cross difference.

4. The frequency of induced cleft palate in F1 embryos from crosses between the strains was higher when the mother was from the A/Jax strain than when the father was—a matroclinous reciprocal cross difference.

5. Since the reciprocal cross differences in frequency of vertebral fusions and for cleft palates were in opposite directions, the hereditary factors influencing susceptibility to the teratogen appear to differ for the respective organ anlage. These differences appear to be, in part, cytoplasmic.

6. The frequency of induced cleft palate in the offspring of backcrosses of (untreated) F1 female hybrids to A/Jax males differed according to the cytoplasmic origin of the F1 mothers. Thus the susceptibility of an embryo to the teratogen appears to be influenced by factors transmitted through the cytoplasm.

The insertion site polymorphism of the copia, mdg1, mdg3, gypsy, and P transposable elements was analysed by in situ hybridization to the polytene chromosomes in genomes of males from a natural population of Drosophila melanogaster. Parameters of various theoretical models of the population biology of transposable elements were estimated from our data, and different hypotheses explaining TE copy number containment were tested. The copia, mdg1 and gypsy elements show evidence for a deficiency of insertions on the X chromosomes, a result consistent with selection against the mutational effects of insertions. On the contrary, mdg3 and P copy numbers fit a neutral model with a balance between regulated transposition and excisions. There is no strong evidence of a systematic accumulation of elements in the distal and proximal regions of the chromosomes where crossing over and ectopic exchanges are reduced. For all chromosome arms but 3L, however, the TE site density increases from the proximal to the distal parts of the chromosomes (the centromeric regions were excluded in this analysis) with sometimes a sharp decrease in density at the extreme tip, following in part the exchange coefficient. The way the copy number of TEs is contained in genomes depends thus on the element considered, and on various forces acting simultaneously, indicating that models of TE dynamics should include details of each element.

Resistance to the cyclodiene insecticide dieldrin maps to a single gene (Rdl) on the left arm of chromosome III in Drosophila melanogaster (Meigen). The gene was further mapped by the use of chromosomal deficiencies to a single letter sub-region, 66F, on the polytene chromosome. The cross-resistance spectrum of a backcrossed strain lacking elevated mixed function oxidase activity, a common resistance mechanism, was examined. Levels of resistance similar to those found in other insects were found to dieldrin, aldrin, endrin, lindane, and picrotoxinin. Strong similarity of this single major gene with that found in other cyclodiene resistant insects is suggested by its cross-resistance spectrum and chromosomal location, via homology with other Diptera. The significance of major genes in insecticide resistance is discussed.

Evidence is presented that the distribution of the combinations of the sexes in twin lambings has subnormal dispersion: there are more opposite-sexed pairs than same-sexed pairs. When adjustment is made for the occasional presence of monozygotic twin pairs, the departure from expectation (on the assumption that the sexes of DZ twins are distributed binomially) is highly significant. Thus sheep litters seem to show a feature characteristic of litters of pigs and (probably) mice and rabbits. This is consistent with the suggestion that p, the probability of a male zygote, varies systematically from one zygote to another within a litter.

The quaking (qk) locus on mouse chromosome 17 has been defined by a single viable quaking allele. Three new alleles of quaking were selected after ENU mutagenesis by their failure to complement the quaking phenotype. The qkk2 allele was induced on wild-type chromatin and the qkkt1 and qkkt4 alleles were induced on t-chromatin. Each is a recessive embryonic lethal mutation. They fail to complement each other and are not complemented by the deletion, TtOrl. Homozygotes and hemizygotes die at 8–9·5 days gestation, but not at a single precise time. Because the classical quaking mutation complements the lethality of these new alleles, but they fail to complement its quaking phenotype (myelination defect), we conclude that the quaking+ function is required for embryonic survival as well as for myelination.

New experimental designs have detected unexpectedly large variations in the time at which macronuclear assortment begins, and in the ratios of the stabilized products. Variation is detected between strains, and, within strains, between conjugating pairs. The Chx locus gave results ranging from late assortment (40–60 fissions) to early assortment with skewed input, indicating the existence of some relation between the parameters of input ratio and time of determination.

The regulation of the syntheses of a number of phosphatases in the fungus Aspergillus nidulans has been examined. Levels of the intracellular alkaline phosphatase P11 are increased by starvation for carbon, nitrogen, phosphorus or sulphur. There is, however, no evidence that any of the wide domain regulatory genes which mediate sufficiency-triggered repression for each of these elements involved. A possible interpretation is that all four forms of starvation result in accumulation of an inducing metabolite. The palcA gene has been identified as a wide domain, probably positive-acting regulatory gene mediating phosphate repression. The palcA product controls the syntheses of alkaline phosphatase PI, acid phosphatases PIII and PV, a phosphodiesterase lacking phosphomonoesterase activity and probably also a phosphate permease. Mutations resulting in derepression of phosphate-repressible activities at acid but not alkaline growth pH define a gene designated pacJ. pacJ mutations also confer arsenate resistance at low but not high pH. It is likely that phosphate derepression and arsenate resistance result from reduced uptake of H2PO4−. Finally, phosphatase regulation might be less complex than previously thought. Mutations designated r and mapping at several loci apparently have no effect on phosphatase. They enhance phosphatase colony staining but this occurs even if the phosphatase substrates are omitted from the staining mixtures. r mutations appear to promote reactions converting the diazonium salts used for phosphatase staining to coloured precipitates.

The number of loci which are potentially able to produce sterility genes was estimated for Drosophila melanogaster. There appear to be, on the second chromosome, about 80 loci capable of producing male sterility and about 60 loci capable of producing female sterility. These figures seem to be considerably less than (400–500) loci responsible for lethal genes.

1. First- and second-generation crosses between killer, neutral and sensitive strains of yeast have been carried out in all combinations.

2. The results of this analysis indicated that the killer character is under the control of two types of cytoplasmic genetic determinant. One type, (k), determines killing, and the other, (n), neutrality. The absence, (o), of both types of determinants confers the sensitive phenotype.

3. That both types of cytoplasmic determinant require the same dominant nuclear allele, M, for their maintenance has been indicated in two ways. First, both types are lost when the nuclear genotype is changed from M to m. Secondly, cells of genotype m(k) or m(n), which have been shown to occur among the first formed cells arising from spores of Mm(k) and Mm(n) diploids respectively, are unable to maintain their cytoplasmic determinants. On the other hand, spore cultures of M(k) and M(n) genotype derived from these same diploide continue to maintain the determinants.

4. Thus genotype of killer cells is M(k), of neutrals M(n), and of sensitivities either M(o) or m(o).

5. Cells maintaining both types of cytoplasmic determinant (i.e. of genotype M(k)(n) or M−(k)(n)) have been obtained by appropriate crosses, and shown to be of killer phenotype.

6. Alternative hypotheses to account for the results of this genetic analysis have been discussed.