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控制侵袭性种群的遗传道效应
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In a population that is not at Hardy-Weinberg equilibrium, the frequency of alleles changes over time. Therefore, any deviations from the five conditions of Hardy-Weinberg equilibrium can alter the genetic variation of a given population. Conditions that change the genetic variability of a population include mutations, natural selection, non-random mating, gene flow, and genetic drift (small population size).
Mechanisms of Genetic Variation
The original sources of genetic variation are...
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Gene flow is the transfer of genes among populations, resulting from either the dispersal of gametes or from the migration of individuals.
This phenomenon plays a significant evolutionary role in all organisms, and depending on the rates of gene flow, the mechanism either induces genetic diversity or generates genetic homogeneity among populations. When the rate of gene flow is low, the introduction of new alleles into a population generates genetic diversity. On the other hand, a high rate of...
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Natural selection—probably the most well-known evolutionary mechanism—increases the prevalence of traits that enhance survival and reproduction. However, evolution does not merely propagate favorable traits, nor does it always benefit populations.
Life is not fair. A deer grazing contentedly in a field can have her meal cut tragically short by a bolt of lightning. If the doomed doe is one of only three in the population, 1/3 of the population’s gene pool is lost. Random...
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Speciation is the evolutionary process resulting in the formation of new, distinct species—groups of reproductively isolated populations.
The genetics of speciation involves the different traits or isolating mechanisms preventing gene exchange, leading to reproductive isolation. Reproductive isolation can be due to reproductive barriers that have effects either before or after the formation of a zygote. Pre-zygotic mechanisms prevent fertilization from occurring, and post-zygotic...
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Small population sizes put a species at extreme risk of extinction due to a lack of variation, and a consequent decrease in adaptability. This weakens the chances of survival under pressures such as climate change, competition from other species, or new diseases. Large populations are more likely to survive pressures such as these, as such populations are more likely to harbor individuals that have genetic variants that are adaptive under new stresses. Small populations are much less...
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Organisms that are well-adapted to their environment are more likely to survive and reproduce. However, natural selection does not lead to perfectly adapted organisms. Several factors constrain natural selection.
For one, natural selection can only act upon existing genetic variation. Hypothetically, red tusks may enhance elephant survival by deterring ivory-seeking poachers. However, if there are no gene variants—or alleles—for red tusks, natural selection cannot...