Microsatellites closely associated with each member of the Tcp1O gene family were amplified simultaneously from t haplotype and wild-type forms of mouse chromosome 17, by PCR. The t complex responder (Tcr) locus, which plays a central role in transmission ratio distortion, maps within the Tcp10 cluster on the t haplotype. Thus the amplified set of microsatellite loci (referred to collectively as Tcp10ms) provides a direct marker for this central component of the meiotic drive system associated with all naturally occurring t haplotypes. A unique Tcp10ms pattern of microsatellite alleles was obtained for a number of independent, laboratory-maintained complete and partial t haplotypes. Independent t chromosomes found in wild mice from US populations also had unique patterns, even when they were classified within the same lethal complementation group. Wild and laboratory chromosomes in the tw5 group showed similarly-sized but non-identical Tcp10ms patterns, suggesting they share a recent common ancestor. These chromosomes are likely to have derived from an ancestral chromosome within the founding population of North American house mice. The Tcp10ms pattern was also shown to be useful in field studies for distinguishing among independentt haplotypes, when more than one is present within a single population.

The species cross between Drosophila melanogaster and D. simulans was first described by Sturtevant in the 1920s. According to his description, the hybridization of D. simulans females and D. melanogaster males produces only (or almost only) male progeny. Female hybrids are embryonic lethal. Here it is shown that these traditional results no longer hold. Instead, D. simulans is polymorphic for factor(s) that qualitatively affect the outcome of species crosses to D. melanogaster. Remarkably, many, if not most, strains of D. simulans produce abundant female hybrids when crossed to D. melanogaster males. Genetic analysis of the difference between D. simulans strains that produce many versus few hybrid females shows that recovery of hybrid females depends on autosomal, maternally acting gene(s).

Gene amplification involving a particular haplotype has been found at the esterase B locus of mosquitoes from various countries. This similarity has been explained by a unique amplification event followed by migration and selection by organophosphate (OP) insecticides. This assumes that the polymorphism of non-amplified esterase haplotypes is so large that the chance of independent amplification in two distinct populations is negligible. In order to test this assumption, three susceptible populations from northern Europe were sampled and analysed for esterase and haplotype polymorphism. At the protein level, 18 and 16 alleles were found for esterase A and B respectively in one French population (n = 74), and 16 and 14 in an English one(n = 50). At the DNA level, 24 alleles at the esterase B locus were detected in a sample of 72 mosquitoes from one population, with the use of only one restrictionenzyme (EcoR V). Restriction maps of two nonamplified haplotypes randomly sampled from a single breeding site in Belgium were built with six restriction enzymes. 60% of all restriction sites were different among the two maps. The huge polymorphism found in northern Europe requires specific explanations for its stability, but it considerably strengthens the hypothesis of migration of amplified haplotypes.

Experiments on Drosophila suggest that genetic recombination may result in lowered fitness of progeny (a ‘recombination load’). This has been interpreted as evidence either for a direct effect of recombination on fitness, or for the maintenance of linkage disequilibria by epistatic selection. Here we show that such a recombination load is to be expected even if selection favours increased genetic recombination. This is because of the fact that, although a modifier may suffer an immediate loss of fitness if it increases recombination, it eventually becomes associated with a higher additive genetic variance in fitness, which allows a faster response to directionselection. This argument applies to mutation-selection balance with synergistic epistasis, directional selection on quantitative traits, and ectopic exchange among transposable elements. Further experiments are needed to determine whether the selection against recombination due to trie immediate load is outweighed by the increased additive variance in fitness produced by recombination.

In plants, models for mapping quantitative trait loci (QTL) based on flanking markers have been mainly developed for progenies of inbred lines. We propose twoflanking marker models for QTL mapping in F1 progenies of non-inbred parents. The first is based on the segregation of four different scorable alleles at a marker locus (the four-allele model) and the second (the commonallele model) on one scorable allele per marker locus segregating in both parents. These models are suitable for the majority of the allelic configurations which may occur in crosses between heterozygous parents. For both cases, when four scorable or one common-allele per marker locus segregate, additional algorithms were developed to estimate the recombination frequency between two marker loci. Tests carried out with simulated populations of various sizes indicate that the models provide a good estimate of QTL genotypic means and of recombination frequencies between flanking markers and between the marker loci and the QTL.The estimates of QTL genotypic means have a higher precision than the estimates of recombination frequencies. The four-allele model shows a higher ability to detect QTLs than the common-allele model. If segregation ratios are distorted, the power of both models and the precision of the estimates of recombination frequencies are reduced, whereas the accuracy of estimates of QTL genotype means is not affected by distorted segregation ratios. The power of the common-allele model is substantially reduced if QTL genotypic means depend on additive allelic interactions, whereas the four-allele model is less affected by the non-additive behaviour of QTL alleles.

The recombination frequency (r) between two loci defined by conventional or molecular markers can be estimated by solving proper Maximum Likelihood equations. These are based on expected and observed marker class frequencies in the progeny of a cross, and are specific for each allelic configuration of the parents(1). In a cross between two diploid parents up to four different alleles, besides a null allele, can be detected at one locus. This defines in each parent, considering a locus A, nine basic allelic configurations based on two allelic marker fragments(Ai/Aj), one single marker allele and a null allele (Ai/AO), or just null alleles (AO/AO). With respect to two loci the consideration of all possible diploid allelic configurations in the parents of a cross allows the detection of 21 different expected marker class distributions producing estimates of r in the progeny. General formulas for calculating the ML equations and the corresponding information functions have been developed for the 21 marker class distributions. Simplified formulas have been also derived and the relative efficiency of the information functions compared. As expected, in the majority of cases, allelic marker configurations give more precise estimates of linkage values than single marker configurations. A method for the construction of linkage maps based on two point estimates, linkage subgroups and allelic bridges is presented. The method is an improvementon an original proposal by Ritter et al.(1990).

The total gametic disequilibrium between two loci linked to polymorphic inversions can be partitioned into two types of components: within and between chromosome arrangements. The within components depend on the gametic disequilibrium within each chromosome arrangement. The between components depend on the locus-inversion disequilibria. This partitioning has practical applications and is indispensable for studying the dynamics of these systems because inversions greatly reduce recombination in the heterokaryotypes while allowing free, and sometimes different, recombination in each of the homokaryotypes. We provide equations for the per generation change of the various disequilibria for systems with two and three chromosome arrangements, and the general recursive equations predicting the disequilibria after any number of generations for the case of two arrangements. Simulation studies were carried out using different values of the recombination parameters and all possible initial conditions. The results show a complex convergence to linkage equilibrium in inversion systems. The various disequilibria can have local maxima and minima while approaching equilibrium and, moreover, their dynamics cannot be described, in general, using a single parameter, i.e. an effective recombination rate. We conclude that the effects of inversions on gametic disequilibria must be carefully considered when dealing with disequilibriain inversion systems. The formulae provided in this paper can be used for such purpose.

We study the dynamics under directional truncation selection of the genetic variability of a quantitative character controlled by a finite number of possibly linked loci with additive effects. After the first generation of selection, the build-up of linkage disequilibria (Bulmer effect) is analytically demonstrated from a genetical point of view in an infinite population. In the following generations, the dynamics of the system in a finite population are predicted using analytic recurrences under a multi-normal approximation, and computer simulations. The effects of recombination on the dynamics of linkage disequilibria induced by selection and drift, and the consequences for the additive genetic variance are then analysed and discussed from the simulation results. Compared to the rapid exploitation of genetic variability promoted by high recombination rates, low recombination rates promote an early storage of genetic variability in repulsion associations of alleles and a possible late release of genetic variance in the population, so that the variability of the character may be maintained over a longer period of time. In some cases, favourable recombination events in tightly linked systems induce an increase of the additive variance of the character, which may explain some results observed in long-term selection experiments. Our results emphasize that the joint effects of selection, linkage and drift must notbe neglected in theoretical quantitative genetics, and require further investigation.