There are two known alleles of the mouse parotid secretory protein (PSP) gene: Pspa and Pspb. Pspa is carried by DBA/2J mice and Pspb is carried by C57BL/6J mice. Eighty-eight mice derived from a F1(C57BL/6J×DBA/2J) to DBA/2J backcross were analysed for PSP mRNA expression in the sublingual glands. Expression was found in heterozygous mice only. This indicates that only Pspb is expressed in this tissue. Furthermore, it maps the allele-specific sublingual gland determinant within 3·4 cM of Psp. Previous analysis of Pspb identified an enhancer-like region in position −4·6 to −3·1 kb that was necessary for transgene expression in the sublingual glands. Here it is shown that the corresponding region in Pspa enhances transgene expression in the sublingual glands as efficiently. The implications for regulation of PSP mRNA expression in the sublingual glands are discussed.

This study is an attempt to trace the fate of hobo elements in the genomes of E strains of Drosophila melanogaster that have been transfected with pHFL1, a plasmid containing an autonomous hobo. Such long-term population studies (over 105 generations) could be very useful for better understanding the population and genomic dynamics of transposable elements and their pattern of insertions. Molecular analyses of hobo elements in the transfected lines were performed using Southern blots of XhoI-digested genomic DNAs. The complete element was observed in all six injected lines. In two lines we observed, at generation 100, two deleted elements, which did not correspond to Th1 and Th2. The results obtained by the in situ method show that the number of hybridization sites increases in each line and prove that the hobo element may be amplified in an RM genome. The hobo activity does not seem to be systematically correlated with the number of hobo elements. After generation 85, the evolution of the hobo element's insertion site number depends on the injected line. In all lines, the total number of insertions remains quite small, between 0 and 11. Hobo elements are located on each of the chromosomal arms. We describe ‘hotspots’ – insertion sites present in all lines and in all generations. On the 3R arm, a short inversion appeared once at generation 85.

Competitions between matched pairs of diploid strains of Saccharomyces cerevisiae, one capable of undergoing sexual recombination (MAT-heterozygous) and the other not (MAT-homozygous), have proved useful for measuring the effects of mitotic and meiotic recombination and DNA repair on competitive ability in this organism. Overall competitive differences between the strains can be enhanced by converting them to petites (aerobic respiration incompetent). Here we report the results of competitions between pairs of strains that also differ in their ability to undergo mismatch repair. In petite strains, the growth rates of mismatch-repair defective strains declined over time regardless of their MAT genotype. Mismatch-repair proficient MAT-heterozygous strains did not show a decline, while repair-deficient MAT-homozygous strains did. The decline appears to be due to the accumulation of deleterious mutations of small effect, which can be corrected by MAT-heterozygous strains having intact mismatch repair. The relative competitive abilities of MAT-heterozygous and MAT-homozygous strains diverged during the course of the competitions, and the variance of this divergence increased significantly when mismatch repair was defective. This large stochastic component indicates that a relatively small number of deleterious mutations may be involved. The accumulation of deleterious mutations and their subsequent repair may have a bearing on the origin of sex in this organism.

A hybrid dysgenesis syndrome in Drosophila virilis is associated with the mobilization of at least four unrelated transposable elements designated Helena, Paris, Penelope and Ulysses. We carried out 42 crosses between eight strains differing in transposable element copy number in order to assess their contributions to hybrid dysgenesis. Linear regression and stepwise regression analysis was performed to estimate the correlation between the difference in euchromatic transposable element number between the parental flies of different strains involved in the crosses and the percentage, in the progeny of these crosses, of males with atrophic gonads. Male gonadal atrophy is a typical manifestation of the D. virilis hybrid dysgenesis syndrome. About half the variability in the level of male gonadal atrophy can be attributed to Penelope and Paris/Helena. Other factors also seem to play a significant role in hybrid dysgenesis in D. virilis, including maternally transmitted host factors and/or uncontrolled environmental variation. In the course of this work a novel transposable element named Telemac was found. Telemac is also mobilized in hybrid dysgenesis but does not appear to play a major causative role.

To clone the Bombyx xanthine dehydrogenase (XDH) gene as a dominant marker for silkworm transgenesis, we performed nested reverse transcriptase–polymerase chain reaction (RT-PCR) using embryonic mRNA and primers designed from the conserved region of Drosophila and rat XDH genes. Sequencing of amplified 180 bp fragments showed that two different sequences were present in the fragments. Since both possessed striking similarity to XDH genes of other organisms, we considered these to be portions of silkworm XDH genes and designated them BmXDH1 and BmXDH2. Subsequently we cloned separately the entire region of the two cDNAs by PCR using phage DNA of an embryonic cDNA library and sequenced them. The two cDNAs were around 4 kb in size and possessed complete open reading frames. The deduced amino acid sequences of the two BmXDHs were very similar to each other and to those of other organisms. The expression pattern of wild-type larvae basically followed the tissue specificity of the enzyme and no significant difference was observed between the two XDH genes. The expression of both genes was detected in the XDH-deficient mutants, oq and og, but non-synonymous substitutions were specifically detected in the BmXDH1 of the oq mutant. In addition, a length polymorphism of the second intron of the BmXDH1 co-segregated with the oq translucent phenotype, suggesting that deficiency in BmXDH1 is the cause of the oq translucent phenotype.

Rapid and divergent evolution of male genitalia represents one of the most general evolutionary patterns in animals with internal fertilization, but the causes of this evolutionary trend are poorly understood. Several hypotheses have been proposed to account for genitalic evolution, most prominent of which are the lock-and-key, sexual selection and pleiotropy hypotheses. However, insights into the evolutionary mechanisms of genitalic evolution are hindered by a lack of relevant in-depth studies of genital morphology. We used a biparental progenies breeding design to study the effects of food stress during ontogeny on phenotypic expression of a suite of genital and non-genital morphological traits, both linear traits and multivariate shape indices, in a natural population of the water strider Gerris incognitus. In general, genitalic traits were as variable as non-genital traits, both phenotypically and genotypically. Average narrow-sense heritability of genital traits was 0·47 (SE=0·05). Further, while food stress during development had a large impact on adult morphology, and expression of genitalic traits exhibited significant levels of condition dependence, different genotypes did not significantly differ in their ability to cope with food stress. Genitalic conformation was also both phenotypically and genetically correlated with general morphological traits. These patterns are in disagreement with certain predictions generated by the long-standing lock-and-key hypothesis, but are in general agreement with several other hypotheses of genital evolution. We failed to find any additive genetic components in fluctuating asymmetry of any bilaterally symmetrical traits and the effects on fluctuating asymmetry of food stress during development were very low and insignificant. Some methodological implications of our study are discussed, such as the bias introduced by the non-negativity constraint in restricted maximum likelihood estimation of variance components.

We have discovered, in an inbred line (Loua) of Drosophila melanogaster from Zaïre, a third chromosome showing unusual P element repression. Repression of P element transposition by this chromosome, named Loua3, is dominant zygotic and has three unusual properties. Firstly, its repression of the gonadal dysgenesis caused by a strong P haplotype is strongly temperature-dependent, being most evident at higher rearing temperatures. Secondly, subdivision of Loua3 by recombination abolishes repression: the effect is apparently a function of the intact chromosome. Finally, Loua3 also diminishes somatic lethality when chromosomes carrying many ‘ammunition’ elements (Birmingham2) are exposed to the constitutive transposase source Δ2-3(99B). The chromosome has 17 P elements, none full-length, located in at least 12 dispersed positions.

The house mouse, Mus musculus, harbours a variable cluster of long-range repeats in chromosome 1. As shown in previous studies, some high-copy clusters such as the MUT cluster are cytogenetically apparent as a homogeneously staining region (HSR) and are associated with a distortion of the Mendelian recovery ratio when transmitted by heterozygous females. The effect is caused by a decreased viability of +/+ embryos. It is compensated by maternal or paternal MUT. In this study, a deletion derivative of MUT, MUTdel, shows normal transmission ratios and no compensating capability. In this respect, MUTdel behaves like a wild-type cluster. Hence, both properties – transmission ratio distortion and compensating capability – map to the deleted region. The deletion comprises three-quarters of the MUT HSR and does not extend to the nearest markers adjacent to the HSR.

The influence of mutation, selection and reproductive systems on within-population size variation at microsatellite loci was analysed using simulations. Mutation occurred through either (biased or unbiased) replication slippage, or unequal recombination between homologous chromosomes. Selection acted either on large allele size, or on the difference in size between the two homologous alleles of an individual. Reproduction was either sexual (panmictic) or clonal. Classical population genetics parameters, such as gene diversity or variance of allele size, were followed over (generally) 5000 generations for various sets of values of the mutation rate and strength of selection, in either clonally or sexually reproducing populations. The reproduction system had little influence on genetic parameters, either under neutral conditions or when selection acted on large allele size. Selection against difference in allele size strongly constrained variability in panmictic populations, whereas a limited influence was observed in clonal populations. Selection against the difference in allele size between the two alleles of an individual is an alternative explanation for the long life expectancy of microsatellite loci in sexual species. Whether this selection process actually occurs can therefore be tested by comparing the allele size distribution of microsatellite loci between regions/genomes exhibiting markedly different recombination rates.

Three new dominant suppressor mutations of the C1 transcription regulator gene in maize – C1-IΔ1, C1-IΔ2 and C1-IΔ3 – are described that suppress anthocyanin colouration in kernels similar to the function of the C1-I standard inhibitor. The C1-IΔ mutations were induced by imprecise excision of an En/Spm transposon in the third exon of the C1 gene. These transposon footprints cause a frameshift in the C1 open reading frame that leads to truncated proteins due to an early stop codon 30 amino acids upstream of the wild-type C1 protein. Therefore, the C1-IΔ gene products lack the carboxy-terminal transcriptional activation domain of C1. The C1-I standard allele also lacks this domain and in addition differs in 17 amino acids from the wild-type C1 allele. The new C1-IΔ alleles provide evidence that deletion of the carboxy-terminal activation domain alone is sufficient to generate a dominant suppressive effect on the function of wild-type C1.

Due to the tremendous cost of the traditional mutation-accumulation approach (the Bateman–Mukai technique), data are rare for deleterious mutation parameters such as genomic mutation rate, selection and dominance coefficients. Two alternative approaches have been developed (the Morton–Charlesworth and Deng–Lynch techniques). Except for the Deng–Lynch method, the statistical properties (bias and sampling variance) of these techniques are poorly understood; therefore we investigated them using computer simulation. With constant fitness effects of mutations, the Bateman–Mukai (assuming additive effects) and Deng–Lynch (assuming multiplicative effects) techniques are unbiased; the Morton–Charlesworth technique (assuming multiplicative effects) is very biased if fitness is used in the regression to estimate h, but slightly biased if the logarithm of fitness is used. With variable fitness effects, all techniques are biased. The Deng–Lynch technique is statistically better than the others except when fitness is used to estimate the average degree of dominance in selfing populations with the Morton–Charlesworth technique. If fitness effects are multiplicative but additivity is assumed, the Bateman–Mukai technique is biased under constant fitness effects, and less biased under variable fitness effects relative to when fitness effects are additive (as assumed by the technique). Our study not only quantifies the degree of bias under the biologically plausible situations investigated, thus forming a basis for correct inference of the true parameters by using these techniques, but also provides insights into the relative efficiencies of these techniques when the same number of genotypes are handled experimentally.

Natural populations of Drosophila kikkawai were collected in India and Sri Lanka, along a latitudinal transect ranging from 6·8° to 31·8° N latitude. Six morphometrical traits were analysed: wing and thorax length, body weight, ovariole number, and abdominal and sternopleural bristle numbers. Significant clines were observed for the three size-related traits and for ovariole number, corresponding to a regular increase in the mean value with latitude, but not for bristle numbers. Due to the utilization of two types of laboratory food, data were distributed into two separate data sets. A low-nutrient food produced smaller flies on average because of more intense crowding. The two rearing conditions produced significant clines but with significantly different slopes. The wing/thorax ratio, which is inversely related to wing loading, also increased with latitude. The analysis of Indian climatic conditions suggested that winter temperature, decreasing from south to north, could be more efficient than summer temperature, which varies in an opposite way, as a selective factor for inducing the clinal variations. The sibling species D. leontia, which is known only from the humid tropics, was found to be much smaller than D. kikkawai and did not fit the clinal regressions. Such morphological differences should help to identify the two species when found in sympatry.

Information on the nature of epistasis between alleles affecting fitness is hardly available, but relevant for, among other issues, our understanding of the evolution of sex and recombination. Evidence of synergistic epistasis between deleterious mutations is support for the Mutational Deterministic hypothesis of the evolution of sex, while finding antagonistic epistasis between beneficial alleles would support the Environmental Deterministic hypotheses. Both types of epistasis are expected to cause negatively skewed fitness distributions of full-sib offspring from a sexual cross. Here, we have studied the form of the distribution of a variety of quantitative characters related to fitness by searching the literature. The fitness traits encountered include the mycelial growth rate in fungi, and earliness, resistance against pathogens, seed number, and pollen fitness in plants. Fitness-related traits in plants show almost exclusively negative skewness, while the results for fungal species are more ambiguous. Possible sources of negative skewness other than epistasis, such as recessiveness of deleterious alleles or a negatively skewed error variance, were tested and found to be unimportant. We argue that these results suggest the existence of synergistic epistasis between deleterious alleles or antagonistic epistasis between beneficial alleles in plants, which is general support for the currently popular hypotheses of sex and recombination, but does not distinguish between them.

A fundamental assumption of models for the maintenance of genetic variation by environmental heterogeneity is that selection favours alternative alleles in different environments. It is not clear, however, whether such antagonistic pleiotropy is common. We mapped quantitative trait loci (QTLs) causing variation for reproductive performance in each of three environmental treatments among a set of 98 recombinant inbred (RI) lines derived from a cross between two D. melanogaster laboratory strains. The three treatments were standard medium at 25°C, ethanol-supplemented medium at 25°C, and standard medium at 18°C. The RI lines showed highly significant genotype–environment interaction for the fitness measure. Of six QTLs with significant effects on fitness in at least one of the environments, five had significantly different effects at the different temperatures. In each case, the QTL by temperature interaction arose because the QTL had stronger effects at one temperature than at the other. No evidence for QTLs with opposite fitness effects in different environments was found. These results, together with those of recent studies of crop plants, suggest that antagonistic pleiotropy is a relatively uncommon form of genotype–environment interaction for fitness, but additional studies of natural populations are needed to confirm this conclusion.

The question of loss of genetic diversity in spatially structured populations has been considered by many authors, who have either assumed symmetric migration between subpopulations or restricted the analysis to two subpopulations and allowed asymmetric migration. In this paper we briefly discuss the two-subpopulation case that has been dealt with by other authors and then find a general formula for fixation probabilities for a population divided into three and four subpopulations. The number of individuals in the subpopulations can be different, but the size of each subpopulation is constant over time. Migration between the subpopulations may be asymmetric, that is the number of migrants moving from subpopulation i to subpopulation j is not the same as the number of migrants moving from subpopulation j to subpopulation i. When migration is symmetric, the results of previous authors are confirmed. The result for asymmetric migration shows that the influence a subpopulation has on the fixation probability for the whole population is determined by its size and the net amount of gene flow out of the subpopulation, directly and indirectly, to the whole population. The position of a subpopulation relative to the other subpopulations (that is, edge versus centre) is only important in that it can determine the amount of net gene flow from a subpopulation. Some examples are given of how this result can be applied, and of applications to conservation genetics. We conclude that when considering a management plan with the intention of maintaining genetic diversity, the relative strength and direction of migration must be considered.

We use modifier theory to compare the evolution of recombination under mutation–selection and migration–selection balance models. Recombination between loosely linked loci subject to weak multilocus selection is controlled by the genotype at a selectively neutral modifier locus. We show that the success of a new modifier depends on the sign and amount of epistasis as well as on the linkage of the modifier locus to the loci under selection. With both migration and mutation, for recombination to increase requires negative (synergistic) epistasis. When epistasis is sufficiently weak, increased recombination is always favoured under mutation–selection balance and never under migration–selection balance. With stronger negative epistasis, there exists a critical recombination value. In this case, a recombination-increasing allele invades the population under mutation–selection balance if its recombination rate with the major loci is less than the critical recombination value, whereas with weak migration it must be above this value. These results are the same for haploid and diploid populations.

A simple regression strategy for mapping multiple linked quantitative trait loci (QTLs) in inbred populations is proposed and applied to data from a non-obese diabetic (NOD) mouse backcross. The method involves adding and deleting markers from a linear model in a stepwise manner, allowing the association with a particular marker to be examined once associations with other (in particular neighbouring) markers have been taken into account. This approach has the advantage of using programs available in standard statistical packages while still allowing adequate separation of possible multiple linked effects. For the mouse backcross, using these methods, at least two and possibly three diabetogenic loci are detected on each of chromosomes 1 and 3. Some evidence for epistasis is seen between the loci on chromosome 1, with a possible additional epistatic interaction between the loci on chromosome 3. Congenic strain analysis of the chromosome regions in NOD diabetes suggests that although the true type I error rate may be larger than that suggested by the nominal P values, our results nevertheless correspond well with those disease loci and interactions detected using a congenic approach, indicating that the regression method may be a powerful strategy for the detection and characterization of QTLs in inbred populations.

A simulation study was performed to investigate methods for mapping single-dose (simplex) and double-dose (duplex) markers, and for identification of homologous chromosomes in an autotetraploid species, and to see how the map accuracy depends on the population size. An initial population of 1000 individuals was simulated, with 30 simplex and 10 duplex markers, and recombination fractions and lod scores were calculated between all pairs of markers. These were used to test the feasibility of mapping the simplex and duplex markers simultaneously. Smaller populations, from 500 to 75 individuals, were then simulated, and the estimates of the pairwise recombination fractions and the derived maps were compared with the true map. It was found that the accuracy of the estimates depended strongly on the type of markers involved, with simplex–simplex coupling pairs being most reliable and simplex–simplex repulsion pairs and duplex–duplex pairs in any configuration but coupling being least reliable. Maps can be assembled using recombination fractions and lod scores from pairs of simplex–simplex markers (coupling and repulsion), duplex–simplex (coupling and repulsion) and duplex–duplex (coupling). The agreement between the map order and the true order was good, although the map distance was generally underestimated at small sample sizes.

In this research we estimated the contribution of a major-gene effect to the control of litter size in hybrids between two local populations of the house musk shrew (Suncus murinus). Segregation analysis was performed on the basis of a mixed polygene and major-gene model. The model presumes that two parental populations may differ from each other in gene frequencies and in the values of polygenic effects but not in the major-gene contribution of the trait. Moreover, the peculiarity of the trait – litter size – is taken into account. This trait is not an individual attribute. It characterizes the parental couple and may depend on the genotypes of both parents. Results of segregation analysis of a large hybrid pedigree of Suncus murinus indicate that the parental populations differ in the allele frequency of the major gene (one population is homozygous, while the other contains the two alleles in approximately equal proportions) and in the values of average polygenic effects. Both major-gene and polygenic components are necessary for the correct description of litter size inheritance in interracial hybrids of S. murinus, inasmuch as the exclusion of either of them leads to a significant drop in likelihood. The Elston–Stewart criterion also confirms the Mendelian inheritance of the major gene.

Methods to formulate and maximize response to selection for a quantitative trait over multiple generations when information on a quantitative trait locus (major gene) is available were developed to investigate and optimize response to selection in mixed inheritance models. Deterministic models with and without gametic phase disequilibrium between the major gene and other genes that affect the trait (polygenes) were considered. Genetic variance due to polygenes was assumed constant. Optimal control theory was used to formulate selection on an index of major gene effects and estimates of polygenic breeding values and to derive index weights that maximize cumulative response over multiple generations. Optimum selection strategies were illustrated using an example and compared with mass selection and with selection with full emphasis on the major gene (genotypic selection). The latter maximizes the single-generation response for a major gene with additive effects. For the example considered, differences between selection methods in cumulative response at the end of a planning horizon of 5, 10, or 15 generations were small but responses were greatest for optimum selection. Genotypic selection had the greatest response in the short term but the lowest response in the longer term. For optimum selection, emphasis on the major gene changed over generations. However, when accounting for variance contributed by the major gene, optimum selection resulted in approximately constant selection pressure on the major gene and polygenes over generations. Suboptimality of genotypic selection in the longer term was caused not so much by gametic phase disequilibrium but rather by unequal selection pressure on the major gene (and, therefore, on polygenes) over generations, as frequency and variance at the major gene changed. Extension of methods to more complex breeding structures, genetic models and objective functions is discussed.