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  • 1985-1989  (3)
  • 1980-1984  (6)
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Year
  • 1
    Electronic Resource
    Electronic Resource
    Linkage Disequilibrium in Natural Populations of Trypanosoma cruzi (Flagellate), the Agent of Chagas’ Disease (1988)
    Oxford, UK : Blackwell Publishing Ltd
    The @journal of eukaryotic microbiology 35 (1988), S. 0 
    Details
    ISSN: 1550-7408
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: . We have studied linkage disequilibrium in natural populations of Trypanosoma cruzi, the agent of Chagas’ disease, by analyzing (i) a set of 524 stocks from the whole geographical range of the parasite, characterized at four gene loci coding for enzymes; (ii) a subsample of 121 stocks characterized at 12 enzyme loci; and (iii) a subset of 386 stocks from six locations in Bolivia, characterized by four enzyme loci. Our results show that the linkage disequilibrium reaches the maximum possible value, given the observed allelic frequencies, for almost all the locus pairs. This result is most consistent with the hypothesis that genetic recombination is absent or very rare in T. cruzi natural populations. Partition of the linkage disequilibrium variance for the six Bolivian populations shows that both inter- and intrapopulation components are substantial and that the relationships among the components are DIS2 〈 DST2, and D'IS2 〈 D'ST2. These inequalities are interpreted as the result of an interplay between genetic drift, rare or absent mating, and clonal selection in generating linkage disequilibrium in T. cruzi populations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1550-7408.1988.tb04081.x
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  • 2
    Electronic Resource
    Electronic Resource
    Satellite DNA sequences and reproductive isolation in theDrosophila willistoni group (1980)
    Springer
    Cellular and molecular life sciences 36 (1980), S. 837-839 
    Details
    ISSN: 1420-9071
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary Satellite DNAs of theDrosophila willistoni group have been analyzed by Hae III endonuclease digestion. Differences were observed between the 2 speciesD. willistoni andD. paulistorum and also between semispecies ofD. paulistorum and, to a lesser extent, between subspecies ofD. willistoni. Differences did not appear to be consistently greater between strains producing sterile hybrid males than between those producing fertile hybrids.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01978600
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    Paper (German National Licenses)
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  • 3
    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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    Paper (German National Licenses)
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  • 4
    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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    Paper (German National Licenses)
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  • 5
    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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  • 6
    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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    Paper (German National Licenses)
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  • 7
    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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  • 8
    Electronic Resource
    Electronic Resource
    Continuous variation: Possible role of regulatory genes (1984)
    Springer
    Genetica 52-53 (1984), S. 1-15 
    Details
    ISSN: 1573-6857
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00121808
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    Paper (German National Licenses)
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  • 9
    Electronic Resource
    Electronic Resource
    Intra- and intergenotypic competition in Drosophila melanogaster: effects of density on larval survival and rate of development (1986)
    Springer
    Genetica 70 (1986), S. 59-67 
    Details
    ISSN: 1573-6857
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract We have examined the effects of density and frequency in the larval competition of Drosophila melanogaster by measuring three fitness components: viability (V), mean development time (MDT) and a combination of these two (E). We have detected (contrary to most published results) non-linear effects of density in single-genotype cultures; in addition, different functions are required to describe the density effects below and above the optimal density. Frequency has also non-linear effects in the two-genotype cultures. Only one polymorphic equilibrium frequency, which is stable, occurs with respect to V; but two polymorphic equilibria, one stable and one unstable, exist with respect to E. The responses in single-genotype cultures do not allow one to predict the outcome of the competition in two-genotype cultures.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00123215
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