Restriction analysis shows that wild Scandinavian mice belonging to the species Mus mtuculus contain the mitochondrial DNA of a neighboring species, M. domesticus. This demonstration results from comparisons of Scandinavian mice with authentic M. dwometicus and M. muscdus from other parts of Europe. Electrophoretic and immunological analysis of eight diagnostic proteins confirms that mice from north of the hybrid zone in Denmark are M. musculus in regard to their nuclear genes. In contrast, the mice tested from this region and a nearby part of Sweden have exclusively M. domesticus types of mitochondrial DNA. Phylogenetic analysis of the restriction maps suggests that the mitochondrial DNAs found in Scandinavian M. musculus could stem from a single M. domesticus female.The growing use of mtDNA as a tool for genetic research on animal populations (1, 2) makes it important to compare the ability of nuclear and mitochondrial genomes to move between populations. [mtDNA differs conspicuously from nuclear DNA not only by being outside the nucleus but also by existing in thousands of copies per cell, being inherited maternally, and evolving quickly (3,4).] Such a comparison can be made by examining the distribution of genes across a hybrid zone-i.e., a geographic zone where two species meet and interbreed but where there is limited flow of nuclear genes (5).Of all the hybrid zones examined by both organismal and molecular biologists, that between two species of mice in Denmark is the best known (6-8). The comprehensive study by Hunt and Selander (7) of proteins encoded by the nuclei of 2,696 mice caught at 44 Danish localities delineated the hybrid zone as regards nuclear genes. In addition, the protein evidence agrees with anatomical evidence as to the geographic location of this hybrid zone (6-8).Further protein work has shown how these Danish mice are related to other commensal mice (9, 10). Commensal mice are those species that live in close association with buildings used by humans. They contrast with aboriginal mice (in Europe: Mus spretus, M. hortulanus, and M. abbotti), which live predominantly independent of human dwellings and, in nature, do not interbreed with commensal mice (10-12). According to a phylogenetic analysis of the protein data, there are two commensal mouse species in Europe. One, known as M. domesticus, lives in southern Denmark, in most of the rest of western Europe, and around the Mediterranean Sea (11, 12) (see Fig. 1). The second, M. musculus, lives in northern Denmark, the rest of Scandinavia, and eastern Europe (11, 12). The hybrid zone defined by Ursin (6) and Selander and co-workers (7, 8) is the meeting place of M. domesticus and M. musculus in Denmark (see Fig. 1). These two types of mice are sometimes considered as semispecies. Our decision to refer to them as separate species is based not only on extensive morphological and biochemical evidence (10-12) but also on the observation that there is a high incidence of sterility in the male offspring of crosses between M. musc...

The extent to which alleles can disperse across a hybrid zone depends on the selection they are subjected to in the hybrid genetic background or, for those that are selectively neutral, on their ability to escape from the unfavourable environment by recombination. Three markers spanning a 45 CM segment in the center of the X chromosome were used to investigate the degree to which selection against X chromosome linked genes helps to maintain the barrier to gene flow in the hybrid zone between A4us musculus domesticus and M. m. musculus in Denmark.The introgression of all the sex chromosome specific markers was more limited than that of the autosomal enzymes (Idh I, Amy, Gpdl, Pgml, Esl, Es2. Mpi, Npl, EslO, Sod]) and the mitochondriul DNA. The cline for DXPus2, which is in the center of the X chromosome, is extremely steep and shows that certain genes located in this region are strongly selected against in the hybrid background.The clines of the other two X-linked markers, Hprt and DXPusl, and of the Y chromosome are not as abrupt and all three have similar asymmetric introgression patterns. Although the musculus variants appear to behave in much the same way as those of the autosomal genes, the domesticus variants do not introgress. The results show that X-linked and to a lesser extent Y-linked genes are more strongly selected against in the hybrid genome than the mitochondrial genome or the different autosomal loci. This suggests that co-adapted gene systems involving the sex chromosomes may play an important role in the hybrid breakdown between the two subspecies.

Hairdressers are highly exposed to skin-damaging substances. The self-reported incidence of hand eczema was substantially higher in female hairdressers than in controls from the general population and than that found previously in register-based studies. For many individuals, onset of hand eczema occurs early in life. Only about 10% of the hand eczema cases among hairdressers would be prevented if no one with skin atopy entered the trade.

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BackgroundExposure to diesel exhaust causes inflammatory responses. Previous controlled exposure studies at a concentration of 300 μg/m3 of diesel exhaust particles mainly lasted for 1 h. We prolonged the exposure period and investigated how quickly diesel exhaust can induce respiratory and systemic effects.MethodsEighteen healthy volunteers were exposed twice to diluted diesel exhaust (PM1 ~300 μg/m3) and twice to filtered air (PM1 ~2 μg/m3) for 3 h, seated, in a chamber with a double-blind set-up. Immediately before and after exposure, we performed a medical examination, spirometry, rhinometry, nasal lavage and blood sampling. Nasal lavage and blood samples were collected again 20 h post-exposure. Symptom scores and peak expiratory flow (PEF) were assessed before exposure, and at 15, 75, and 135 min of exposure.ResultsSelf-rated throat irritation was higher during diesel exhaust than filtered air exposure. Clinical signs of irritation in the upper airways were also significantly more common after diesel exhaust exposure (odds ratio=3.2, p<0.01). PEF increased during filtered air, but decreased during diesel exhaust exposure, with a statistically significant difference at 75 min (+4 L/min vs. -10 L/min, p=0.005). Monocyte and total leukocyte counts in peripheral blood were higher after exposure to diesel exhaust than filtered air 20 h post-exposure, and a trend (p=0.07) towards increased serum IL-6 concentrations was also observed 20 h post-exposure.ConclusionsDiesel exhaust induced acute adverse effects such as symptoms and signs of irritation, decreased PEF, inflammatory markers in healthy volunteers. The effects were first seen at 75 min of exposure.