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Initial Population

After Ab treatment. Initial Population. New Population. Evolution is the change in the relative frequency of alleles in a population NOTE the word population Individuals evolve!!!

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Initial Population

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  1. After Ab treatment Initial Population New Population

  2. Evolution is the change in the relative frequency of alleles in a population • NOTE the word population • Individuals evolve!!! • For example; take a stable population of bugs that are about 50% light colored and 50% dark. Over time, less and less dark ones are seen and the population now has about 80% light and 20% dark. So what is evolution anyway? DO NOT

  3. Theory of Evolution Darwinism 

  4. Darwin noticed that the finches on the Galapagos Islands all had different beaks though the islands are incredibly isolated. • He reasoned that likely only a couple of finches founded the population but mutations over time allowed them to eat different foods. These new beaks kept getting passed on and eventually led to different species. So What does darwin have to do with it?

  5. Darwin called this idea that the organisms that are better able to survive and reproduce: natural selection. • Mutations that lead to better camouflage, for example, allow those organisms to survive, then reproduce, and slowly, the population changes. This is evolution. So What does darwin have to do with it?

  6. Natural selection is a mechanism by which evolution can occur. • It works through individuals, but the population is what evolves • Requires 3 conditions • Genetic variability • Trait is heritable • Leads to differentiated reproduction Natural Selection

  7. Mutations in gene pool • These mutations are random; there is no “ideal” • Changes in environment • Habitat • Climate • Niche What triggers the change?

  8. An organism has 3 choices in responding to environmental pressures: • Adaptation • Migration • Extinction • Without a changing environment, natural selection & evolution would not occur Environmental changes

  9. Evolution does not happen in the same way across all populations. • Natural Selection on a single gene can just change the allele frequencies (like the peppered moth) • With polygenic traits, it’s more complicated. Evolution can occur via: • Directional Selection • Stabilizing Selection • Disruptive Selection Is all evolution the same?

  10. In this case, individuals on ONE END of the population curve are better adapted to their environment. Ex: If you look at beak size, you have birds with a medium beak as the majority, with small and large beaks on each end of the curve. If a drought occurs and only the very large seeds survive, only large-beaked birds will be able to eat Directional Selection

  11. When the average individual is best, the population stabilizes – reducing the percentage of organisms on the extremes. Ex: Birth weight in humans has become stable within a range because too small is harmful for the baby and too big have difficulties during the birthing process. Stabilizing Selection

  12. This occurs when either extreme is better adapted for survival than the average. Ex: Most of a species of butterfly are brown. But on either end of the population curve, you see red and blue. These brightly colored butterflies resemble very poisonous butterflies and thus do not get eaten. Disruptive Selection

  13. In small populations, the percentages of alleles change more quickly – this is called genetic drift. • If populations get separated and each new population only has two of the four variations, you have a founder effect. Small populations

  14. A species is defined as a group of organisms that can interbreed and produce fertile offspring. • All of these subtle changes over time can eventually lead to a new species. So how do we get a new species?

  15. Population become geographically isolated from each other • Each “new” population will respond differently and to different selective pressures. • If they change so much that if, when back together, they could not produce fertile offspring, then speciation has occurred. Allopatric speciation

  16. This type of speciation occurs when organisms that could interbreed do not due to differences in timing or rituals. Ex: orchids will grow on the same branch of a tree but do not interbreed because they release pollen at different times Sympatric speciation

  17. Gradualism – when evolution occurs slowly over time (most of what we have talked about) • Punctuated equilibrium – when a major event changes the distribution of a population…leads to a quick burst of changes since mutations spread quickly through small populations • Founder effect, genetic drift How fast can evolution occur?

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