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  • Articles: DFG German National Licenses  (23)
Source
  • Articles: DFG German National Licenses  (23)
Material
Years
  • 11
    Electronic Resource
    Electronic Resource
    Adaptation by natural selection in populations ofDrosophila pseudoobscura (1970)
    Springer
    Cellular and molecular life sciences 26 (1970), S. 208-208 
    Details
    ISSN: 1420-9071
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Resumen Seis poblaciones deDrosophila pseudoobscura han evolucionado, debido a la selección natural, hacia una mayor adaptación al ambiente. Durante 20 o 25 generaciones el número de individuos nacidos por unidad de comida y el tamano de la poblacion han aumentado gradualmente entre un dos y un cuatro por ciento por generaciön.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01895587
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  • 12
    Electronic Resource
    Electronic Resource
    Wineries, drosophila, alcohol, and Adh (1980)
    Springer
    Oecologia 47 (1980), S. 141-144 
    Details
    ISSN: 1432-1939
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Previous workers (McKenzie and Parsons, 1972, 1974; McKenzie, 1974; Briscoe et al., 1975) have found anomalous distributions of species of Drosophila, of sexes of D. melanogaster, and of Adh alleles in and around wineries in Australia and Spain. Field studies in California's Sonoma Valley provide evidence that the explanations advanced for these distributions may incorrect. The anomalous distribution of species was attributed to alcohol, either as a selective agent or as a behavioral stimulus. We find a virtually identical species distribution in the absence of environmental alcohol. The anomalous sex ratio was attributedd to differential survivall of the sexes when raised on alcohol. We present crude evidence thatehe difference may simply be a behavioral response to some product of fermentation, which need not be alcohol. Finally, the allele frequency difference reported from Spain was attributed to differential adult mortality on alcohol. We do not find an allele frequency difference even when alcohol is exposed, and therefore suggest that selection is occurring in pre-adult stages.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00541790
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  • 13
    Electronic Resource
    Electronic Resource
    Genetic polymorphism: from electrophoresis to DNA sequences (1983)
    Springer
    Cellular and molecular life sciences 39 (1983), S. 813-823 
    Details
    ISSN: 1420-9071
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary Recent studies indicate that the amount of protein variation undetected by electrophoresis may be reasonably small. Nevertheless, at the protein level, a typical sexually-reproducing organism may be heterozygous at 20 or more percent of the gene loci. Although the evidence is limited, it appears that at the level of the DNA nucleotide sequence every individual is heterozygous at every locus — if introns as well as exons are taken into account. The evidence available does not support the hypothesis that, at least at the protein level, the variation is adaptively neutral.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01990397
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  • 14
    Electronic Resource
    Electronic Resource
    The enigma of intron origins (1999)
    Springer
    Cellular and molecular life sciences 55 (1999), S. 3-6 
    Details
    ISSN: 1420-9071
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s000180050264
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  • 15
    Electronic Resource
    Electronic Resource
    Overcompensation as a mechanism for maintaining polymorphism: egg-to-adult viability in Drosophila (1990)
    Springer
    Genetica 82 (1990), S. 183-187 
    Details
    ISSN: 1573-6857
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Frequency-dependent selection may be accounted for, in ecological terms, by the differential effectiveness of alternative genotypes in exploiting limiting environmental resources. Differentiation in resource exploitation among genotypes implies in turn that a mix of genotypes may exploit more fully the resources than a genetically uniform population, a phenomenon called ‘overcompensation’ Experiments designed to test for overcompensation whow that highly polymorphic populations can support larger numbers of individuals per food unit than less polymorphic populations. This difference cannot be attributed to the level of individual heterozygosity, which is the same in both types of populations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00056361
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  • 16
    Electronic Resource
    Electronic Resource
    Effects of allozyme variation on fitness components in Drosophila melanogaster (1983)
    Springer
    Genetica 62 (1983), S. 139-146 
    Details
    ISSN: 1573-6857
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract We have explored in Drosophila melanogaster the fitness effects of allelic variation at three enzyme loci: α Gdh, Adh, and Acph. Viability and rate of development are studied at two densities, near-optimal and competitive. No genotypic effects could be demonstrated on rate of development at either density or on viability under optimal conditions. Small but significant effects on viability appear under competitive conditions. Fecundity is measured for all nine possible mating combinations between the three female and the three male genotypes at each locus. Female genotype has important fitness consequences; heterosis exists at every locus. Male genotype also contributes to fitness, but without heterosis. There are significant interactions between female and male genotypes, so that the fecundity of a mating combination cannot be determined from the average fitnesses of the female genotype and the male genotype involved.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00116635
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  • 17
    Electronic Resource
    Electronic Resource
    Biochemical genetics of chromosome forms of Venezuelan spiny rats of the proechimys guairae and proechimys trinitatis superspecies (1979)
    Springer
    Genetica 50 (1979), S. 89-97 
    Details
    ISSN: 1573-6857
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Spiny rats from Venezuela show an extensive karyotypic diversification (2n=24 to 2n=62) and little morphological differentiation. This study reports genetic distance, heterozygosity and polymorphism based upon 22 loci in semispecies and allospecies of the Proechimys guairae superspecies from N Central Venezuela, as compared with Proechimys urichi, a member of the Proechimys trinitatis superspecies from eastern Venezuela. Four chromosome forms of the P. guairae complex are included, each characterized by karyotypes of 2n=46 (Fundamental Number=72), 2n=48 (FN=72), 2n=50 (FN=72) and 2n=62 (FN=74). Proechimys urichi has a distinetive karyotype of 2n=62 (FN=88). The overall mean value of Nei's genetic identity index for all pair-wise comparisons is I=0.942±0.011. Mean identity within the P. guairae complex is Ī=0.969±0.033. Mean identity between P. urichi and members of that complex is Ī=0.889±0.011. Within the P. guairae complex, increased genetic divergence is correlated with higher karyotypic divergence. Heterozygosity varies from H=0.059 to H=0.153, with a mean value of H0.059. The mean percent of polymorphic loci is P=18.2±3.9 after the ‘0,95%’ polymorphism criterion, and P=20,5±5.2 after the ‘0.99%’ criterion. These results are compared with similar data from fossorial and non-fossorial rodents. Spiny rats are non-fossorial, forest-dwelling rodents which have undergone a speciation process with little genetic divergence and extensive chromosome rearrangements.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00123283
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  • 18
    Electronic Resource
    Electronic Resource
    Correlation between recombination frequency and fitness in Drosophila melanogaster (1981)
    Springer
    Genetica 56 (1981), S. 61-69 
    Details
    ISSN: 1573-6857
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The origin and maintenance of genetic recombination are unsettled evolutionary issues. Genetic variation affecting recombination frequency appears to be pervasive in nature, suggesting that natural selection must increase recombination frequency under some circumstances. However, theoretical arguments and experimental evidence indicate that the frequency of recombination should be reduced by natural selection. A hypothesis not previously explored is that recombination modifiers may directly affect the fitness of their carriers; rather than only indirectly (through the production of recombinant progeny) as generally assumed. We have tested this hypothesis by examining three fitness components (viability, male fertility, and female fecundity) in Drosophila melanogaster homozygous for second chromosomes isolated from a natural population. Then, we have measured the frequency of recombination in flies heterozygous for each wild second chromosome and a chromosome carrying five recessive alleles. The results indicate that genes modulating the frequency of recombination have direct effects on fitness as proposed by the hypothesis. However, the correlation between frequency of recombination and fitness is negative. Thus, the riddle of recombination remains unexplained and, in fact, more puzzling that ever.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00126931
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  • 19
    Electronic Resource
    Electronic Resource
    Fitness of allozyme variants in Drosophila pseudoobscura III. Possible factors contributing to the maintenance of polymorphisms in nature (1977)
    Springer
    Genetica 47 (1977), S. 65-70 
    Details
    ISSN: 1573-6857
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Experiments have been performed to investigate the mechanisms maintaining enzyme polymorphisms in natural populations. We have measured effects on fitness of genotypic variants at three loci, Est-5, Odh, and Mdh-2, in D. pseudoobscura. Significant differences exist among the genotypes in the rate of development from egg-to-adult; there is also indication of differences in larval survival. In a population segregating for allelic variants at all three loci, there is indication that segregation distortion at meiosis or some form of gametic selection might be involved. The relative fitnesses of alternative genotypes are reversed when either different fitness components are considered, or the genotypic frequencies are changed, or the larval density is increased. These fitness reversals may contribute to the maintenance of the polymorphisms, and may account for cyclical oscillations of allozyme frequencies observed in natural populations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00122441
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  • 20
    Electronic Resource
    Electronic Resource
    Genetic variation for rate of development in natural populations of Drosophila melanogaster (1986)
    Springer
    Genetica 71 (1986), S. 123-132 
    Details
    ISSN: 1573-6857
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract We have sampled wild chromosomes from two natural populations of Drosophila melanogaster and obtained flies fully homozygous for the second chromosome, the third chromosome, or both, as well as flies heterozygous for one or both wild chromosomes and balancer chromosomes. Rate of embryogenesis (egg laying to larval hatching) and rate of development from egg to adult are measured, by classifying the individuals into fast, intermediate, and slow developmental classes. The experiments indicate that variation for rate of embryogenesis and for rate of egg-to-adult development is plentiful in the natural populations. Various hypotheses are enunciated to account for the small range of phenotypic variation observed in wild-type individuals with respect to the two parameters (embryogenesis and egg-to-adult development) and for the difficulty in changing the mean rates by artificial selection. Appropriate experiments may decide among the hypotheses, helping us to understand the genetic control of rate of ontogenesis, which is an important fitness component.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00058695
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