We have constructed a linkage map of random amplified polymorphic DNAs (RAPDs) in Bombyx mori. We screened 320 10-mer primers, and found 243 clear polymorphic bands between C108 and p50 strains. In the F2 generation, segregation ratios of 168 bands were nearly 3:1 in a chi square test, showing Mendelian inheritance. The MAPMAKER program sorted 168 bands into 29 linkage groups and 10 unlinked loci at minimum LOD score 3·0, and determined orders of loci in each group, which contained 2–11 markers. It also detected typing errors in our data. We calculated map distances between pairs of neighbouring loci using recombination values in males and the Kosambi mapping function. Our RAPD map consists of 169 loci including the p locus, and the sum of map distances is approximately 900 cM. Linkage groups 1 and 2 of our map correspond to chromosomes 1 and 2 on the conventional linkage map because of linkage to sex and p, respectively.

The effective population size is required to predict the rate of inbreeding and loss of genetic variation in wildlife. Since only census population size is normally available, it is critical to know the ratio of effective to actual population size (Ne/N). Published estimates of Ne/N (192 from 102 species) were analysed to identify major variables affecting the ratio, and to obtain a comprehensive estimate of the ratio with all relevant variables included. The five most important variables explaining variation among estimates, in order of importance, were fluctuation in population size, variance in family size, form of N used (adults υ. breeders υ. total size), taxonomic group and unequal sex-ratio. There were no significant effects on the ratio of high υ. low fecundity, demographic υ. genetic methods of estimation, or of overlapping υ. non-overlapping generations when the same variables were included in estimates. Comprehensive estimates of Ne/N (that included the effects of fluctuation in population size, variance in family size and unequal sex-ratio) averaged only 0·10–0·11. Wildlife populations have much smaller effective population sizes than previously recognized.

We present data for the initial construction of a molecular linkage map for the domesticated silkworm, Bombyx mori, based on 52 progeny from an F2 cross from a pair mating of inbred strains p50 and C108, using restriction fragment length polymorphisms (RFLPs). The map contains 15 characterized single copy sequences, 36 anonymous sequences derived from a follicular cDNA library, and 10 loci corresponding to a low copy number retrotransposon, mag. The 15 linkage groups and 8 ungrouped loci account for 23 of the 28 chromosomes and span a total recombination length of 413 cM; 10 linkage groups were correlated with established classic genetic maps. Scoring data from Southern blots were analysed using two Pascal programs written specifically to analyse linkage data in Lepidoptera, where females are the heterogametic sex and have achiasmatic meiosis (no crossing-over). These first examine evidence for linkage by calculating the maximum lod score under the hypothesis that the two loci are linked over the likelihood under the hypothesis that the two loci assort independently, and then determine multilocus linkage maps for groups of putatively syntenic loci by calculating the maximum likelihood estimate of the recombination fractions and the log likelihood using the EM algorithm for a specified order of loci along the chromosome. In addition, the possibility of spurious linkage was exhaustively tested by searching for genotypes forbidden by the absence of crossing-over in one sex.

In Drosophila, the three yolk protein (yp) genes are transcribed in a sex-, tissue- and developmentally specific manner, providing an ideal system in which to investigate the factors involved in their regulation. The yolk proteins are synthesized in the fat body of adult females, and in the ovarian follicle cells surrounding the developing oocyte during stages 8–10 of oogenesis. We report here an analysis of the yolk protein 3 (yp3) gene and its flanking sequences by means of P-element mediated germ-line transformation and demonstrate that a 747 bp promoter region is sufficient to direct sex-specific expression in the female fat body and both the temporal- and cell-type-specificity of expression during oogenesis. Two elements that independently govern yp3 transcription in these tissues have been separated and no other sequences in the upstream, downstream or coding regions have been identified that are autonomously involved in yp3 expression.

The t haplotypes are variant forms of the proximal one-third of chromosome 17 in the mouse. They contain four inversions (relative to the wildtype DNA) extending over most of this region and house a number of male sterility factors. Males carrying two complete t haplotypes (t/t) are sterile, as are males homozygous for S2, the sterility factor located in the most distal (relative to the centromere) inversion. Males homozygous for the sterility factor S1, located in the most proximal inversion, are not sterile; however, if such a male also is heterozygous for other sterility factors, then sterility results. It has been suggested therefore that homozygosity for S1 enhances the detrimental action of other sterility factors. Sperm from t/t males have severe motility defects and are unable to penetrate investment-free eggs, while sperm from fertile t/+ mice have less serious motility defects and exhibit a delay in penetration of investment-free eggs. To determine whether homozygosity for S1 enhances the cellular defects exhibited by sperm from mice heterozygous for other sterility factors, we compared the motility and egg-penetrating ability of sperm from fertile mice homozygous for S1 to that of sperm from mice carrying one complete t haplotype and one proximal or distal partial t haplotype. The data suggest that sperm from males carrying a proximal partial t haplotype and a complete t haplotype have serious defects in motility and penetration of the investment-free egg, and support the hypothesis that S1 enhances the detrimental effects of other sterility factors within the t haplotype.

Fifty-six accessions of Triticum monococcum and one accession each of T. beoticum and T. sinskajae were analysed for their storage protein compositions and breadmaking quality as determined by the SDS-sedimentation test. In total 30 different alleles at the Glu-A1m locus coding for high-molecular-weight glutenin subunits (HMW-GS), 25 alleles at the Gli-A1m locus coding for ω- and γ-gliadins and 45 alleles at the Gli-A2m locus controlling the synthesis of α/β-gliadins were detected. Most accessions contained one x-type and one y-type HMW-GS and two genotypes were null for both types of subunits. Two polypeptides within the mobility range of HMW-GS in SDS-PAGE were shown to be ω-type gliadins encoded by genes on the short arm of chromosome 1 A. T. sinskajae and several ‘monococcum’ accessions were shown to share the same alleles at Gli-A1m, Gli-A2m and Glu-A1m, confirming sinskajae as a subspecies of T. monococcum. The SDS-sedimentation volumes of most accessions were very low (11–35 ml), a few accessions showing mean sedimentation volumes as high as 90–93 ml. Through the comparison between biotypes occurring in some accessions of ‘monococcum’, good bread-making quality was found to be associated with the presence of alleles y, c and i at the Gli-A1m locus. All accessions were resistant to leaf rust and rich in protein (≥ 16·5%), and most of them showed resistance to powdery mildew.

Published reports suggest that the incidence of monozygotic twinning in women is increased after hormonally induced ovulation. Since some statistical evidence exists to indicate that monozygotic twinning may also occur in mice, we attempted to devise a mouse system in which the incidence of such twinning could be compared after spontaneous versus hormonally induced ovulation, in order to analyse the developmental basis of such an effect. We used phenotypic identity in litters segregating for ten genetic loci (not all independent) to indicate possible twin pairs. DNA fingerprinting using three human minisatellite probes was then performed blind on these pairs and on sibling controls. From a total of over 2000 mice born, 40 apparently identical pairs were identified, on which DNA finger-printing was successfully carried out on 35 pairs. All proved to be derived from different zygotes. We conclude that monozygotic twin pairs are either extremely rare in the stock of mice that we studied, or have such reduced viability that their chance of surviving to weaning is low.

A method based on the animal model is described which allows the estimation of continuous changes in variance components over time using restricted maximum likelihood (REML). The method was applied to the analysis of a selection experiment in which a foundation population formed from a cross between two inbred strains of mice (C57BL/6J and DBA/2J) was divergently selected for 6 week body weight over 20 generations. The analysis suggested that there was an increase in phenotypic variance of about 50% in the low selected lines over the course of the experiment which was attributed to increases in the environmental and additive variance components. Variance changes in the High selected lines were generally smaller than in the Low lines, although there was an estimated 20% increase in the environmental variance. Simple models to explain these effects involving dominance, linkage and epistasis were explored. Testing which of these was responsible for the variance changes noted in this experiment (if any) is difficult, although the epistasis and dominance models require less stringent conditions than the linkage model, and the dominance model is supported by evidence of heterosis in the F1.

Lines of mice have been selected for up to 50 generations on the following traits: high body weight, low body weight, high fat content or low fat content. The lines selected for high or low body weight differ by a factor of 2·5 and those selected for high or low fat content differ by a factor of five, both traits measured in 10 week old males. A set of behavioural traits was measured to ascertain whether this selection had caused correlated responses in behaviour: studies included feeding behaviour, open field behaviour, ultrasound calling rates of pups, and the response to the introduction of a novel physical object. Alterations in behavioural patterns which were expected a priori were observed but there appeared to be no changes in behaviour associated with any one selection criterion. Estimates of the genetic correlations between selected and behavioural traits were, with one exception, generally less than 0·1 in magnitude and not significantly different from zero (the exception was food intake in lines selected on body weight). Assuming that mice are accurate models for commercial species, then these results have important implications for animal welfare: they demonstrate that large scale behavioural changes do not arise as an inevitable consequence of intense long-term selection on traits of economic importance in commercial species

We have investigated the distribution of resistance genes in relation to genetic structure and gene flow between various islands of French Polynesia in Culex pipiens quinquefasciatus. We show that (1) resistance to organophosphorous insecticides, mediated by A2–B2 esterases, is present in all islands, (2) A2–B2 frequency decreases as distance from Tahiti increases, and (3) genetic differentiation (measured as estimates of the Fst, parameter from allozyme polymorphism) between islands is significantly correlated to geographic distances which is also correlated to air or sea commercial traffic. These data are discussed in relation to A2–B2 invasion of French Polynesian islands.

Transpositive mutagenesis was employed to prepare genetic strains useful in cloning the Virescent-1 locus (V1) of maize. A stepwise approach was used based on: (1) the isolation of putative insertion phenotypes (62 cases); (2) the verification of the genetic nature of the selected events (36 v1-m mutant alleles induced); (3) the accurate genetic study of 11 alleles; (4) the genetic assessment that the alleles v1-m1 and v1-m4 are due to the insertion of a Ds element into the locus V1; (5) the proof that a Ds-like DNA element induces the inactivation of the wild type function in the allele v1-m1. The phenotype of the unstable alleles, studied by germinating and keeping maize seedlings at the temperature of 18 °C, are the following: alleles v1-m1, v1-m9, v1-m11, v1-m17 and v1-m18 showing a few revertant green sectors on their leaves; v1-m4 exhibiting a reverse type of variegation; alleles v1-m2 and v1-m13 with a coarse pattern of variegation; alleles v1-m12, v1-m21 and v1-m23 frequently showing leaves part green with white stripes and part white with green stripes. For the alleles studied, in addition to somatic instability, germinal reversions also occurred. In some cases, these reversions resulted in stable derivatives with a different colour from that of the wild-type (‘near green’ or pale phenotypes). The results presented not only allow the v1-m1 allele to be chosen as a starting material for cloning the V1 locus, but also define the molecular strategy to be followed.

Oocytes from (C3H/HeH × 101/H)F1 and Rb(16.17)7Bnr homozygous females were exposed to a range of doses of nocodazole in vitro. The spindle poison caused a dose dependent increase in metaphase I (MI) arrest and hyperploidy. A concentration of 0·03 μg/ml was found to induce a maximum hyperploid frequency of 3·1% and 11·6% respectively without a high level of MI arrest. Between 0·03 and 0·05 μg/ml MI arrest increased substantially and reached a frequency of approximately 90%. In a further experiment oocytes from Rb7 homozygous, heterozygous and 3H1 females were exposed to 0·03 μg/ml nocodazole 4, 6 or 8 h after the onset of maturation. The phase at which the spindle was inhibited resulted in a specific pattern of nondisjunction which in turn was dependent on whether the female carried an Rb metacentric. 3H1 oocytes gave a normally distributed pattern of increase in aneuploid frequency (over the spontaneous value) centering around a 6 h application. This was thought to be due to the interaction of chromosomes with the microtubules of the spindle during attachment and/or alignment. In contrast both Rb homozygotes and heterozygotes gave the same biphasic response, with a high frequency of aneuploidy in the oocytes when nocodazole was applied 4 and 8 h after the onset of maturation. In Rb homozygotes we demonstrated that the Rb bivalent underwent nondisjunction more frequently than the average acrocentric, when nocodazole was administered early. It can be assumed that the Rb trivalent in Rb heterozygotes showed a similar response. This early Rb specific effect, in combination with a delayed-version of the acrocentric effect found in the 3H1 mice was thought to generate the biphasic pattern. We discuss the implications of (a) the different meiotic behaviours of metacentrics and acrocentrics and (b) the meiotic delay in Rb mice.

The effects of partial inbreeding on effective population size and rates of fixation of mutant genes are investigated in selected populations. Truncation selection and an infinitesimal model of gene effects for the selected trait are assumed. Predictions of effective size under this model are given for partial selfing and partial full-sib mating and an extension to a more general model is outlined. The joint effect of selection and partial inbreeding causes a large reduction in the effective size relative to the case of random mating. This effect is especially remarkable for small amounts of selected genetic variation. For example, for initial heritability 0·1 and proportion selected 1/6, the ratio of effective size to population size is 0·10 in populations with about 90% selfing while it is 0·85 in random mating populations. The consequence is a reduction in the fixation probability of favourable genes and, therefore, a reduction in the final response to selection. Stochastic simulations are used to investigate the effects of partial inbreeding and selection on fixation and extinction rates of genes of large effect and of recessive lethals with effects on the selected trait. For genes of very large effect, the effective size is not a critical factor and it is expected that partial inbreeding will be efficient in increasing fixation rates of recessive mutants. Lethal recessives are eliminated more frequently and their equilibrium frequency is lower under partial inbreeding, but only when their effects on the heterozygote are not very large.

Two ecotypes have been described for Culex pipiens mosquitoes of the temperate zone: a human commensal type and a feral type, but their degree of evolutionary differentiation and taxonomic status are still unclear. The commensal form is characterized by life-history traits probably adaptive to underground man-made environments. This situation has sometimes been considered as an example of recent speciation although the existence of intermediate forms indicates that the balance between gene flow and disruptive selection should first be assessed. The present study was concerned with (1) the determination of biological traits involved in adaptation to commensalism, and (2) the pattern of gene flow within and between ecotypes in a restricted area. It was found that (1) significant differences in biological traits exist between mosquitoes from different habitats, (2) characteristics of the commensal type are not universal in mosquitoes from underground man-made habitats, (3) allozyme markers do not clearly differentiate ecotypes and (4) insecticide resistance genes, which reveal recent migration, occur in each ecotype. These results are discussed in the context of possible speciation due to commensalism.

Divergent artificial selection for abdominal bristle number in Drosophila melanogaster has been carried out starting from a genetically homogeneous base population. Lines with two different systems of mating, random (P lines) or between full sibs whenever possible (about 50%), random otherwise (I lines) were compared. Responses after 40 generations of selection were mostly due to one or two mutations of large effect (0·2 to 2 phenotypic standard deviations) per line. Ten mutations affecting the selected trait were individually studied (five lethal and five non-lethal, these being predominantly additive). These mutations satisfactorily explain the response attained, although some minor mutations may also be involved. No evidence of epistasis for bristle number was found. The average final divergence was 57% larger in the P lines, but it was mostly due to lethals or highly deleterious mutations. Thus, after relaxation of selection, the ranking reversed and the mean divergence became significantly larger in the I lines (14%). Analysis of inbreeding showed that the very small amount of variation created by spontaneous mutations (a heritability for the selected trait of about 3%) was responsible for a reduction in the effective size of about 50% in the I lines (relative to the case with random selection), but only about 10% in the P lines. Mutational heritabilities estimated from the response to selection (0·05–0·18%) were within the range usually found for this trait in previous experiments. REML estimates account for correlations between relatives, and were much larger in those lines where the response was due to lethal mutations, as these do not contribute to response after reaching maximum frequency.

The distribution of 13 transposable element families along 15 X chromosomes from an African natural population of Drosophila simulans was determined by in situ hybridization to polytene chromosomes. The transposable elements cloned from Drosophila melanogaster all hybridized with Drosophila simulans chromosomes. The number of copies per family was 3·5 times lower in the latter species and correlated with the copy number per family in Drosophila melanogaster. With the exception of 297, the copy number per chromosome followed a Poisson distribution. Element frequencies per chromosome band were generally low. However, several sites of the distal region and the base of the X chromosome had high frequencies of occupation. Elements had higher abundance at the base of the chromosome compared to distal regions. Overall, the distribution of transposable elements in Drosophila simulans is similar to that found in Drosophila melanogaster. These data provide evidence for the operation of a force (or forces) opposing transpositional increase in copy number, and that this force is weaker at the bases of chromosomes, consistent with the idea that recombination between elements at non-homologous sites contains TE copy number. The reduction in copy number of all TE families in Drosophila simulans compared to Drosophila melanogaster can be explained by stronger selection against transposable element multiplication and/or lower rates of transposition in Drosophila simulans.

A high frequency of proviral acquisition has previously been reported in the offspring of SWR/J–RF/J hybrid mice. In the present study, it was investigated whether this proviral acquisition would be useful for large-scale insertional mutagenesis studies. A population of SWR/J–RF/J hybrid mice with a predominantly SWR/J background was created. Lines of mice with such a background and partially congenic for two active proviruses from the RF/J strain were generated (the insert lines). Control lines were derived from mice which had no proviral loci but had an otherwise similar genetic background. DNA samples of mice in the insert lines were screened for the appearance of new proviral loci by Southern hybridization. The rate of proviral acquisition, calculated from the observed number of new proviral loci was 0·023 new proviruses per mouse. This rate is lower than found in previous studies and too low for large-scale insertional mutagenesis studies. A sensitivity experiment indicated that there was adequate detection of new proviral loci.The number of segregating proviruses was consistent with the number of newly acquired proviruses actually detected. Two additional crosses between mice in the insert lines and SWR/J mice were performed. The rate of proviral acquisition was greatly increased when SWR/J females were initially mated to insert mice, but remained unchanged when SWR/J males were used. This suggested that mice in the insert lines had acquired a maternally transmitted factor, which was suppressing viral expression and thus reducing the rate of proviral acquisition.

A general approach is developed to estimate secondary selection at a modifier locus that influences some feature of a population under mutation-selection balance. The approach is based on the assumption that the properties of all available genotypes at this locus are similar. Then mutation-selection balance and weak associations between genotype distributions at selectable loci and the modifier locus are established rapidly. In contrast, changes of frequencies of the modifier genotypes are slow, and lead to only slow and small changes of the other features of the population. Thus, while these changes occur, the population remains in a state of quasi-equilibrium, where the mutation-selection balance and the associations between the selectable loci and the modifier locus are almost invariant. Selection at the modifier locus can be estimated by calculating quasiequilibrium values of these associations. This approach is developed for the situation where distributions of the number of mutations per genome within the individuals with a given modifier genotype are close to Gaussian. The results are used to study the evolution of the mutation rate. Because beneficial mutations are ignored, secondary selection at the modifier locus always diminishes the mutation rate. The coefficient of selection against an allele which increases the mutation rate by υ is approximately υδ2/[U(2−ρ)] = υŝ, where υ is the genomic deleterious mutation rate, δ is the selection differential of the number of mutations per individual in units of the standard deviation of the distribution of this number in the population, ρ is the ratio of variances of the number of mutations after and before selection, and ŝ is the selection coefficient against a mutant allele in the quasiequilibrium population. However, the decline of the mutation rate can be counterbalanced by the cost of fidelity, which can lead to an evolutionary equilibrium mutation rate.

Previous work which appeared to show that some strains of mice taste glycine solutions as bitter has been found to be in error. The bitterness came from copper glycinate which formed in the brass drinking spouts. Taste testing with copper glycinate shows that the genetical data identifying the gene Glb are still valid. The close linkage of Glb and Rua has been confirmed. Most strains of mice prefer glycine solution to water, presumably because the glycine tastes sweet. The degree of preference for glycine is correlated with the degree of preference for other sweet substances such as saccharin or acesulfame. The gene dpa appears not to be involved.

The sweetness tasting gene Sac has been mapped to chromosome 4 at 8·1 ± 3·4 cM distal to Nppa (formerly Pnd). The bitterness tasting gene Soa is very closely linked to Prp on chromosome 6 (no recombinants among 67 backcross progeny). It is suggested that the sweetness and bitterness tasting genes have descended from a common ancestral tasting gene which existed before the tetraploidization of the genome which took place in early vertebrate evolution.