types of natural selection

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11 Terms

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what is selection pressure?

an environmental factor which causes selection within a population by exerting environmental pressure

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examples of selection pressure

predatation, disease, temperature variation, human influence, limited light oxygen and water, competition

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what is the limiting factor due to?

the phenotype, which limits reproductive success as well as selection pressure

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any natural selection question:

  1. mutation results in new allele

  2. those new allele have the advantage of

  3. individuals with the allele are more likely to survive and reproduce

  4. increased frequency of this allele in a population

  5. directional selection

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what is directional selection?

shifts mean value of the phenotype in the direction that the extreme phenotype is favoured by selection.

<p>shifts mean value of the phenotype in the direction that the extreme phenotype is favoured by selection. </p>
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what does directional selection do over time?

individuals at one extreme may have an advantage, leading to selection to operate against the disadvantadged extreme and in favour of the other extreme, causing a shift in the population's traits - the mean and range of values shift towards the favoured extreme.

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example of directional selection

occurs when there is a change in environment

cheetahs - individuals with the speed allele more likely to catch prey than slower individuals. They have a select advantadge so they’re more likely to survive, reproduce and pass on their alleles. Over time, the frequency of alleles for high speed increases and the population becomes faster.

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<p>what is stabilising selection?</p>

what is stabilising selection?

reduces variation but doesn’t change the mean, by favouring average phenotypes over extremes, promoting traits that are average and limiting the prevalence of extreme traits, to make it more uniform.

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<p>example of stabilsiing selection</p><img src="https://knowt-user-attachments.s3.amazonaws.com/fa863ad5-77ea-4dd1-995a-b6f398c06807.jpg" data-width="100%" data-align="center" alt="knowt flashcard image"><p>occurs when there is no change in environment</p>

example of stabilsiing selection

knowt flashcard image

occurs when there is no change in environment

Human birth weight, where infants of average weight have higher survival rates compared to those that are underweight or overweight. Over time, proportion of population with average birth weight increases and range decreases, resulting in a narrower offspring graph

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what happens to standard deviation as the individuals with extreme traits decrease

The standard deviation decreases (stabilising selection).

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sequence of events leading to natural selection

  1. competition

  2. genetic variation within population - random mutations leading to stabilising selection

  3. combinations of alleles make them better able (fitter) to survive

  4. so more successful breeding and more offspring produced

  5. successful reproduction means alleles passed on through generations and the frequency of adventaageous alleles increases.