| 词汇 | example_english_genetic-drift |
| 释义 | Examples of genetic driftThese examples are from corpora and from sources on the web. Any opinions in the examples do not represent the opinion of the Cambridge Dictionary editors or of Cambridge University Press or its licensors. Given enough time, geneticdrift results in the fixation or loss of alleles at particular loci. These data suggest that purifying selection removes deletion variation before it is fixed in populations, but that insertions are capable of fixing through geneticdrift. Molecular markers to study geneticdrift and selection in wheat populations. This is because geneticdrift drives deleterious mutants to high frequencies for all mating systems. Thus, each year the worms were subjected to selection pressure during 2 steps, and to geneticdrift during 22 steps. When populations are small, effects of geneticdrift are more important. The interaction between selection against partially recessive mutations and geneticdrift in small populations also influences the rate of decay of neutral variation. The biology of the crop would suggest that in its natural habitat, 'populations' could evolve by geneticdrift into isolation, inlocalities such as river valleys. Two forces affect the inbreeding and geneticdrift at neutral loci linked to loci under selection. The forces that cause differentiation for these markers would be the result of mutation, geneticdrift and no selection. On the other hand, parasites from such host populations may also be less variable, because they themselves experience geneticdrift, and therefore less virulent. During the establishment of these populations, bottlenecks and the effects of geneticdrift may result in unrepresentative genotypic distributions and loss of variation. There can be no doubt that evolutionary potential is reduced by geneticdrift and inbreeding in small populations. The process of differentiation of the frequencies of non-selected ancestral alleles in different taxonomic groups due to geneticdrift begins immediately after a speciation event. Given that distance estimators based on allele frequencies rely on geneticdrift, they are sensitive to changes in population size. This is due to the selection of a small number of parents (a single parent in these simulations), analogous to the phenomenon of geneticdrift. Image scoring only works in case of strong geneticdrift or a very small cost of actually being altruistic. Geneticdrift in clines which are maintained by migration and natural selection. Randomly distributed crossovers may generate block-like patterns of linkage disequilibrium : an act of geneticdrift. Furthermore, these traits are significantly associated with eco-geographical factors, consistent with selection for local adaptation rather than geneticdrift. In phase 1 geneticdrift causes sub populations to cross adaptive valleys, and consequently occupy different regions of the adaptive landscape to one another. In addition to random geneticdrift, there are many possible reasons for such a difference. Factors such as random geneticdrift can therefore maintain the system far from equilibrium. Therefore, not only geneticdrift, but also mutation pressure affects allele frequencies. During this process, some types of element could have been lost randomly by geneticdrift. Our model and estimation procedure assume that the population is sufficiently large for the effect of geneticdrift to be ignored. Apparently, equilibrium element number decreases sufficiently that geneticdrift can result in fixation of element-free genotypes, even in large populations. This further suggests that mutation and geneticdrift alone cannot explain the evolution of microsatellite loci in the long term. Self-fertilization is known to increase spatial structure, by enhancing geneticdrift and reducing gene flow because of diminished pollen dispersal. Inbreeding reduces the effective population size, and consequently enhances the effect of geneticdrift. In populations fragmented into small subpopulations, as assumed in our study, geneticdrift has an important effect on the distribution of allele (and genotype) frequencies. The simplest situation modelled is a random-mating population with stable demography at genetic equilibrium between mutation and geneticdrift. Despite low genetic differentiation among infrapopulations and a high mean intensity of parasite infection, geneticdrift may exert an important effect on the population. Their dispute over the relative importance of geneticdrift in changing gene frequencies extended over more than a quarter of a century. The variance due to random geneticdrift has been calculated on the basis that there would be no mutation, selection or intermixture. The phenomena originating these modules could also be based on geneticdrift, recombination processes and different selective immune pressures. Inbreeding facilitates the selective elimination of partially recessive deleterious mutations, while geneticdrift hinders the purging process and may drive the deleterious mutations to fixation. Repeated population bottlenecks lead to losses in genetic variation because of random geneticdrift. This is then used to demonstrate that cultural and geneticdrift are operating in similar ways. Geneticdrift, in contrast to selection, causes completely different changes in allele frequencies within populations. Linkage disequilibrium at steady state determined by random geneticdrift and recurrent mutation. However, significant correlations were established between these traits and eco-geographical factors, consistent with spatial heterogeneity selection rather than geneticdrift. Inbreeding and coancestry could be explained parsimoniously by fewer ancestors capturing the whole information due to geneticdrift. In many predominantly selfing populations, geneticdrift is likely to result in loss of all elements. In other words populations should evolve under geneticdrift or driftmutation alone. Firstly, a geneticdrift might have taken place in the laboratory-bred strain over the intervening years due to the effect of subculturing. Indeed, most genetic polymorphisms used in population genetic studies are assumed to be neutral and affected mainly by both mutation and geneticdrift. These data are indicative of the existence of geneticdrift that is most probably maintained by limited gene flow. Selection, migration and mutation are assumed to be unimportant in changing allele frequencies compared with geneticdrift. Our model and estimation procedure assume that the population is sufficiently large for geneticdrift effect to be ignored. With geneticdrift, it is assumed that adult population size is the sample size and each adult produces an effectively infinite number of seeds. Design and analysis of experiments on random geneticdrift and inbreeding depression. The intention of the present study was to explore the role of natural selection and geneticdrift on the degree of inversion polymorphism. But in small populations, the role of geneticdrift can become significant, in addition to mutation and selection. This slows down the turnover of generations and thus reduces geneticdrift and inbreeding. Another issue that has not received much attention in previous studies on purging is the interactions among inbreeding, geneticdrift and selection. The programme consisted of a succession of generations that were submitted to anthelmintic treatment or to putative geneticdrift only. Secondly, the local dynamics may impose geneticdrift on populations and limit the amount of variation. The interesting aspect is that gene diversity will strongly depend upon geneticdrift. There are several reasons that suggest strong geneticdrift in populations of digeneans. An accumulation of clashing loci could occur if fluctuations are accompanied by isolation (no migration) or by a large amount of geneticdrift. The second term of the denominator refers to the geneticdrift due to the variable contribution from parents. However, our results cannot be compared directly with those from analytic formulas derived by these authors, since geneticdrift was not considered in the present study. We compute the expected mean and variance of the distribution of marker allele frequency changes under the null hypothesis (geneticdrift) and the alternative hypothesis (directional selection). This is because different lines in a population are no longer independent, and more lines result in less geneticdrift and stronger selection against the deleterious mutations. If the optimum phenotype changes further in this direction more switches become necessary (in practice, random geneticdrift will play a role in determining which of the loci switch). Second, it reduces the effective population size applicable to the polygenes, the loss of their variation from geneticdrift contributing further to the loss in polygenic genetic response. Dominant conditions with low reproductive fitness show little regional variation in frequency, but milder conditions may show variation as a result of founder effect or geneticdrift. The great success of some invasions is therefore perhaps surprising, given that founder effects and geneticdrift might be expected to result in low genetic variation in colonizing species. Geneticdrift and estimation of effective population size. Natural selection and random geneticdrift in phenotypic evolution. While mutation is the ultimate source of this variation, the role of other evolutionary forces (selection, migration and random geneticdrift) in maintaining variation is generally unknown. Geneticdrift : the problem and its possible solution by frozen-embryo storage. The author considers a miscellaneous collection of observations and problems, and demonstrates how they are each consistent with mutation and geneticdrift as primary determinants of molecular evolution. In small populations, it is not the deterministic forces but the stochastic factor, random genetic drift, that is the major determinant of genetic structure of the populations. If the selection pressures are not divergent, but fluctuating, an escalating build-up of clashes is unlikely unless accompanied by peripheral isolation or high levels of geneticdrift. Recurrent introduction, founder effect, random geneticdrift, and/or selection pressure caused by biotic and abiotic factors would also contribute to the final genetic make-up of the introduced population. When the goal is to compare populations, these methods should in principle not be used when migration remains strong enough to blur the influence of geneticdrift and mutation. Geneticdrift alone is unlikely to drive genetic differentiation over such a small number of generations, unless it is accompanied by extreme bottlenecks and/or selection. Secondly, some mutants of small effect are fixed in small populations due to geneticdrift, permanently lowering the fitness of the population, and probably endangering its long-term survival. After 20 generations of inbreeding, selection and geneticdrift, mutations at most loci are lost while others are driven to much higher frequencies than the initial value (1\\120). For the experiments mentioned above, an appropriate statistical method should be developed to ensure that the observed frequency changes are due to selection rather than random geneticdrift. The reduction in fitness from geneticdrift at heterotic loci in small populations. Farmers need only buy new seed after five to seven years when farm-saved seed starts losing its vigour (giving lower yields) or suffering from 'geneticdrift'. The differences observed between some of the clines may reflect subtle differences in selection against fusions when heterozygous, but they also may be due to sampling or geneticdrift. Often these populations become genetically differentiated through geneticdrift, mutation and\\or divergent selection, and this differentiation can be reduced by migration among populations or uniform selection. In a highly subdivided population, a deleterious mutation quickly becomes either eliminated from or fixed in a line due to the high rate of inbreeding and geneticdrift within lines. Since the populations are largely clonal, this may enhance geneticdrift. From Wikipedia This example is from Wikipedia and may be reused under a CC BY-SA license. These can be caused by geneticdrift or by mutation, and they will tend to slow down the process of evolution. From Wikipedia This example is from Wikipedia and may be reused under a CC BY-SA license. This, however, is fallacious, given that evolution is not a completely random effect (geneticdrift), but rather proceeds with the aid of natural selection. From Wikipedia This example is from Wikipedia and may be reused under a CC BY-SA license. These examples are from corpora and from sources on the web. Any opinions in the examples do not represent the opinion of the Cambridge Dictionary editors or of Cambridge University Press or its licensors. |
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