178,370 research outputs found
Phylogeography of five Polytrichum species within Europe
No full textUsing allozymes and microsatellites we have analysed the genetic structure among European populations for several Polytrichum species to infer relevant factors, such as historical events or gene flow, that have shaped their genetic structure. As we observed low levels of genetic differentiation among populations, and no decreasing levels of genetic variation with increasing latitude within most of the examined species, no genetic evidence was obtained for a stepwise recolonization of Europe from southern refugia after the latest glacial period for R. commune, P. uliginosum, R formosum and R piliferum. The near absence of population substructuring within these species does indicate that extensive spore dispersal is the most important factor determining the genetic structure among European Polytrichum populations. Gene flow levels have apparently been sufficient to prevent genetic differentiation among populations caused by genetic drift, and to wipe out any genetic structure caused by the postglacial recolonization process. On the other hand, increased genetic differentiation of alpine R formosum populations suggests that mountain ranges might restrict gene flow significantly among Polytrichum populations. In contrast to most examined Polytrichum species, R juniperinum showed high levels of genetic differentiation and a profound genetic structure. Assuming that gene flow is not more restricted in P. juniperinum, these findings suggest that this species has recolonized Europe after the latest glacial period from two different refugia, one possibly being the British Isles. (C) 2003 The Linnean Society of London
Polymorphism at the G6pd and 6Pgd loci in Drosophila melanogaster: IV. Genetic factors modifying enzyme activity
No full textThe significance of genetic erosion in the process of extinction: I. Genetic differentiation in Salvia pratensis and Scabiosa columbaria in relation to population size
No full textAs part of a programme to determine the importance of the loss of genetic variation for the probability of population extinction, the amount of allozyme variation was determined in 14 populations of Salvia pratensis and in 12 populations of Scabiosa columbaria. Significant correlations were found between population size and the proportion of polymorphic loci (Salvia: r = 0.619; Scabiosa: r = 0.713) and between population size and mean observed number of alleles per locus (Salvia: r = 0.540; Scabiosa: r = 0.819). Genetic differentiation was substantially larger among small populations than among large populations: in Salvia G(ST) was 0.181 and 0.115, respectively, and in Scabiosa 0.236 and 0.101, respectively. The results are discussed in relation to genetic drift, inbreeding and restricted gene flow
The alcohol dehydrogenase polymorphism in Drosophila melanogaster: Fitness measurements and predictions under conditions with no alcohol stress
No full textCharacterization of conditionally expressed mutants affecting age-specific Drosophila melanogaster: Lethal conditions and temperature-sensitive periods
No full textThe specific genetic basis of inbreeding depression is poorly understood. To address this question, two conditionally expressed lethal effects that were found to cause line-specific life span reductions in two separate inbred lines of Drosophila melanogaster. were characterized phenotypically and genetically in terms of whether the accelerated mortality effects are dominant or recessive. The mortality effect in one line (14) is potentially a temperature-sensitive semilethal that expresses in adult males only and is partially dominant. The other line (110) responds as one would expect for a recessive lethal. It requires a cold shock for expression and is cold sensitive. Flies exhibiting this lethal condition responded as pupae and freshly eclosed imagoes. The effect is recessive in both males and females. The expression of the lethal effects in both lines is highly dependent upon environmental conditions. These results will serve as a basis for more detailed and mechanistic genetic research on inbreeding depression and are relevant to sex and environment-specific effects on life span observed in quantitative trait loci studies using inbred lines
Changes in genetic architecture during relaxation in Drosophila melanogaster selected on divergent virgin life span
No full textArtificial selection experiments often confer important information on the genetic correlations constraining the evolution of life history. After artificial selection has ceased however, selection pressures in the culture environment can change the correlation matrix again. Here, we reinvestigate direct and correlated responses in a set of lines of Drosophila melanogaster that were selected on virgin life span and for which selection has been relaxed for 10 years. The decrease in progeny production in long-lived lines, a strong indication of antagonistic pleiotropy, had disappeared during relaxation. This was associated with a higher cost of reproduction to long-lived flies in mated, but not in virgin life span. These data strongly suggest that genetic mechanisms of mated and virgin life span determination are partly independent. Furthermore, data on body weight, developmental time and viability indicated deleterious effects of longevity selection in either direction, giving rise to a nonlinear relationship with life span for these characters. In order to reclaim original patterns, we founded a new set of derived lines by resuming selection in mixed replicate lines of the original set. Although selection was successful, most patterns in correlated characters remained, showing that these new patterns are resistant to new episodes of selection
The effect of DDT on the polymorphism at the G6pd and Pgd loci in Drosophila melanogaster
No full textPolymorphism at the G6pd and 6Pgd loci in Drosophila melanogaster: III. Developmental and biochemical aspects
No full textPloidy level and somatic chromosome number variation in Agrostis stolonifera
No full textAgrostis stolonifera is a polyploid complex in which clonal propagation is predominant. Polyploidization often results in the induction of chromosomal aberrations at the mitotic and/or meiotic level. We observed that variation in ploidy level was present in Agrostis stolonifera, and that variation in chromosome number within genotypes also occurred. Populations differed in the degree of variation observed. Analysis of the frequency distribution of chromosome numbers per cell among different populations showed a wide range of variation in the inland meadow population, an intermediate level in the polder and salt marsh populations, and a very low level in the sand dune population. The results are discussed in the context of the origin of somatic chromosome number variation
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