Examples of stabilizing selection in the following topics:
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- Stabilizing, directional, and diversifying selection either decrease, shift, or increase the genetic variance of a population.
- If natural selection favors an average phenotype by selecting against extreme variation, the population will undergo stabilizing selection.
- As a result of this stabilizing selection, the population's genetic variance will decrease.
- Stabilizing selection occurs when the population stabilizes on a particular trait value and genetic diversity decreases.
- Different types of natural selection can impact the distribution of phenotypes within a population.In (a) stabilizing selection, an average phenotype is favored.In (b) directional selection, a change in the environment shifts the spectrum of phenotypes observed.In (c) diversifying selection, two or more extreme phenotypes are selected for, while the average phenotype is selected against.
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- Natural selection drives adaptive evolution by selecting for and increasing the occurrence of beneficial traits in a population.
- Natural selection only acts on the population's heritable traits: selecting for beneficial alleles and, thus, increasing their frequency in the population, while selecting against deleterious alleles and, thereby, decreasing their frequency.
- Natural selection does not act on individual alleles, however, but on entire organisms.
- Natural selection acts at the level of the individual; it selects for individuals with greater contributions to the gene pool of the next generation, known as an organism's evolutionary fitness (or Darwinian fitness).
- Through natural selection, a population of finches evolved into three separate species by adapting to several difference selection pressures.
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- Farmers developed ways to select for plant varieties with desirable traits long before modern-day biotechnology practices were established.
- Because foreign genes can spread to other species in the environment, extensive testing is required to ensure ecological stability.
- The Ti plasmids carry antibiotic resistance genes to aid selection and can be propagated in E. coli cells as well.
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- In frequency-dependent selection, phenotypes that are either common or rare are favored through natural selection.
- Another type of selection, called frequency-dependent selection, favors phenotypes that are either common (positive frequency-dependent selection) or rare (negative frequency-dependent selection).
- An interesting example of this type of selection is seen in a unique group of lizards of the Pacific Northwest.
- In this scenario, orange males will be favored by natural selection when the population is dominated by blue males, blue males will thrive when the population is mostly yellow males, and yellow males will be selected for when orange males are the most populous.
- Negative frequency-dependent selection serves to increase the population's genetic variance by selecting for rare phenotypes, whereas positive frequency-dependent selection usually decreases genetic variance by selecting for common phenotypes.
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- Natural selection cannot create novel, perfect species because it only selects on existing variations in a population.
- However, natural selection cannot produce the perfect organism.
- Natural selection can only select on existing variation in the population; it cannot create anything from scratch.
- Natural selection is also limited because it acts on the phenotypes of individuals, not alleles.
- This a common example of disruptive selection.
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- The regulation of population growth by these factors can be used to introduce a classical concept in population biology: that of K-selected versus r-selected species.
- For this analysis, population biologists have grouped species into the two large categories, K-selected and r-selected, although they are really two ends of a continuum.
- K-selected species are those in stable, predictable environments.
- Populations of K-selected species tend to exist close to their carrying capacity (hence the term K-selected) where intraspecific competition is high.
- In contrast to K-selected species, r-selected species have a large number of small offspring (hence their r designation).
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- Sexual selection, the selection pressure on males and females to obtain matings, can result in traits designed to maximize sexual success.
- The selection pressures on males and females to obtain matings is known as sexual selection.
- Sexual selection takes two major forms: intersexual selection (also known as 'mate choice' or 'female choice') in which males compete with each other to be chosen by females; and intrasexual selection (also known as 'male–male competition') in which members of the less limited sex (typically males) compete aggressively among themselves for access to the limiting sex.
- Females, on the other hand, tend to get a handful of selected matings; therefore, they are more likely to select more desirable males.
- Sexual selection can be so strong that it selects for traits that are actually detrimental to the individual's survival, even though they maximize its reproductive success.
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- Charles Darwin and Alfred Wallace independently developed the theories of evolution and its main operating principle: natural selection.
- Darwin called this mechanism natural selection.
- These tortoises were "selected" because they could reach more leaves and access more food than those with short necks.
- Natural selection, Darwin argued, was an inevitable outcome of three principles that operated in nature.
- His book outlined his arguments for evolution by natural selection.
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- Natural selection can only occur in the presence of genetic variation; environmental conditions determine which traits are selected.
- The same traits are not always selected because environmental conditions can change.
- The direction of natural selection shifted so that plants with small leaves were selected because those populations were able to conserve water to survive the new environmental conditions.
- Natural selection acts on individual organisms, which in turn can shape an entire species.
- Explain why only heritable variation can be acted upon by natural selection
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- In mating, there are two types of selection (intersexual, intrasexual) and three mating systems (monogamous, polygynous, polyandrous).
- These types are: intersexual selection (the choice of a mate where individuals of one sex choose mates of the other sex) and intrasexual selection (the competition for mates between species members of the same sex).
- Intersexual selection is often complex because choosing a mate may be based on a variety of visual, aural, tactile, and chemical cues.
- An example of intersexual selection is when female peacocks choose to mate with the male with the brightest plumage .
- Differentiate among monogamous, polygynous, and polyandrous mating systems, and distinguish between intersexual and intrasexual mate selection