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Biology 11: Processes of Evolution
Name: _________________________
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Biology 11: Processes of EvolutionUnit Learning Goals
C5 Describe the five agents of evolutionary change: mutation, genetic
drift, gene flow, non-random mating, and natural selection (pp 264-265)
(pp 268-275)
C6 Understand the concept of speciation (macroevolution)
C7 Compare gradual change model with the punctuated equilibrium
model of evolution
Part A: Darwin’s Theory of Evolution
-Darwin’s 5-year voyage on the Beagle provided him with many pieces of evidence to demonstrate that Evolution has occurred.
-Darwin’s Theory of Evolution by Natural Selection is his explanation for how organisms have adapted to their environment.
-Darwin was influenced by his observations of Artificial Selection. Examine the diagrams right and explain this concept.
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-What are some other examples of artificial selection?
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-The diagram right illustrates Darwin’s idea of natural selection, except that he did not know about alleles.
-Lamarck, a French naturalist (1744-1829), proposed that Giraffe’s long necks evolved because they were needed. How would Darwin have explained this?
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-How does natural selection differ from artificial selection?
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-Pesticide application to agricultural fields is an example of how humans can inadvertently cause natural selection to occur. This reveals three things about natural selection:
a) Natural selection is an editing and not a creative process.
b) Natural selection is time and space specific.
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c) Evolutionary change can occur in a short time span.
Part B: Genetics and The Modern Theory of Evolution
-Since Darwin, many additions have been made to the Theory of Evolution
by means of Natural Selection. Genetics, in particular, has been incredibly
important in explaining how natural selection operates.
-Below are some important terms and ideas we have to know about before
we look further into the Modern Theory of Evolution:
a) A population is a ____________________________________________
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b) Alleles are _________________________________________________
c) What does it mean for an individual to be homozygous for a trait? And heterozygous?
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d) How are genotypes different from phenotypes?
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e) Examine the diagram below. What is the gene pool and allele frequency of a population?
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f) Microevolution is a___________________________________________________________________
Part C: Hardy-Weinberg Equilibrium
-Since Darwin’s time, scientists have studied how populations evolve, and they have extended his ideas to include other processes, besides natural selection, that can cause populations to evolve.
-The Hardy-Weinberg Equilibrium states that the frequency of alleles in a gene pool will remain constant over time unless five agents of microevolution are present:
1. Mutations
-Mutations are changes in the arrangements of nucleotides in DNA.
-Where must mutations occur if they are to affect a population’s genetic variability?
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-Remember that mutations can be harmful, neutral or helpful.
2. Genetic Drift
-Examine the diagram right. How is genetic drift different from natural selection?
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-Would the impact of genetic drift be felt more in a small population or a large population?
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-There are several different types of Genetic Drift:
a) Bottle Neck Effect
-The Bottle Neck Effect is a type of genetic drift where the population size is dramatically reduced by a natural disaster.
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-What consequence has this had for Prairie Chickens?
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-Pingelap Island is another example of this, where the rate of colourblindness is much higher than other populations due to a bottleneck event. This resulted in the recessive alleles for this disorder being present at a higher frequency in the post-disaster gene pool.
b) Founder Effect
-Differences in the gene pool of a small colony compared to the original population.
-How will the colony size affect how closely it resembles the original population genetically?
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-Tristan da Cunha is an example of this, where 15 British people founded the colony and 1 had the recessive allele for progressive blindness. By the 1960s, the rate of occurrence was 10x that of the rate found in the original population.
3. Gene Flow
-Is the movement of genes in and out of a population.
-How could this occur?
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-What is the over-all effect of gene flow?
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4. Non-Random Mating
-What characteristics do organisms usually look for in choosing a mate?
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5. Natural Selection
-Natural selection is the survival of the fittest, where the best adapted organism will survive and reproduce at a higher rate. This means that it will pass its genes onto the next generation at a higher rate.
Part D: Natural Selection
-In your own words, explain why natural selection is the only mechanism that consistently leads to adaptive evolution. Section 13.2 in your text will be helpful in doing so.
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-Three types of natural selection alter the genetic variation of a population’s gene pool:
1. Stabilizing Selection
-The intermediate group (clutch size) has the highest rate of survival and reproduction.
2. Directional Selection
-Over many generations, one of the phenotypes has the highest rate of survival and reproduction.
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3. Disruptive (or Diversifying) Selection
-Under what conditions might this type of natural selection occur?
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Part E: Speciation and Macro-Evolution
-Why are donkeys and horses not considered the same species?
-Members of the same species produce fertile, viable offspring.
1. Types of Reproductive Isolation
-There are several pre-zygotic and post-zygotic barriers that prevented organisms from reproducing together:
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2. Types of Speciation
-What is the difference between Allopatric and Sympatric speciation?
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-What cannot occur between populations undergoing these two types of speciation?
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-What type of speciation are the chipmunks below showing?
*Explore this idea further by examining the allopatric speciation of lizards animation.
3. Hybrid Production
-Examine the diagram right. What does it indicate about the two toad population? Are they one species or two?
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-Populations undergoing speciation can have three possible results depending on the strength of reproductive barriers:
4. Adaptive Radiation
-What is adaptive radiation?
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-Molecular analysis indicates that the species of Hawaiian depicted are all descended through allopatric and sympatric speciation from an ancestral tarweed that arrived 5 million years ago from North America.
5. Models of Evolutionary Change
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-Examine the two models of evolutionary change depicted right. How are they different from each other?
-Gradualism:
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-Punctuated Equilibrium:
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Part F: Test Your Understanding
-Is evolution goal oriented?
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-Try the concept map below:
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