BIOLOGY: Chapter 16

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BIOLOGY Chapter 16 The Evolution of
Populations Speciation

• Warm-Up (pg 292)
• Compare contrast convergent and divergent
  evolution (include examples).

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Section 16-1 Genetic Equilibrium

• Section 16-1 Objectives
• (1) The student will be able to explain the
  importance of the bell curve to population
  genetics.
• (2) The student will be able to describe 2 causes
  of genotypic variation in a population.
• (3) The student will be able to explain how to
  compute allele frequency and phenotype frequency.
• (4) The student will be able to explain
  Hardy-Weinberg genetic equilibrium.

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Section 16-1 Genetic Equilibrium

• Variation of Traits in a Population
• Population genetics- the study of evolution from
  a genetics perspective
• Population- collection of individuals of the same
  species that interbreed its the smallest unit
  in which evolution can occur
• Bell Curve (Fig 16-1, pg 299)- many traits in a
  population show variation that follows this curve
  (i.e., height and weight).
• Causes of Variation
• A. Environmental factors (i.e., food)
• B. Heredity
• C. Variations in genotypes
• 1. Mutation
• 2. Recombination during meiosis
• 3. Random fusion of gametes

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Section 16-1 Genetic Equilibrium

• Allele Frequencies The Gene Pool
• Gene pool the total genetic info available in a
  population
• Allele frequency (pg 300) divide the of a
  certain allele by the total of alleles of all
  types in a population.
• Predicting Phenotype (Fig 16-3, pg 301)
• Phenotype frequency equals of individuals w/a
  particular phenotype divided by total of
  individuals in a population

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Section 16-1 Genetic Equilibrium

• Hardy-Weinberg Genetic Equilibrium
• Wilhelm Weinberg, a German physician, Godfrey
  Hardy, a British mathematician, independently
  showed allele frequencies in a population remain
  the same through each generation unless
  influenced by outside sources.
• Its based on a set of assumptions about an
  ideal hypothetical population that is NOT
  evolving (real populations may violate
  conditions needed for genetic equilibrium where
  allele frequencies dont change each generation)
• 1. NO mutations
• 2. Individuals dont leave a population
• 3. Large population
• 4. Random mating
• 5. NO selection
• http//en.wikipedia.org/wiki/Hardy-Weinberg_princi
  ple

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Section 16-2 Disruption of Genetic Equilibrium

• Section 16-2 Objectives
• (1) The student will be able to list 5 conditions
  that can cause evolution to occur.
• (2) The student will be able to give an example
  of how migration can effect evolution.
• (3) The student will be able to define genetic
  drift, and tell how it affects endangered
  species.
• (4) The student will be able to contrast the
  effects of stabilizing, directional, and
  disruptive selection on variations in a trait
  over time.
• (5) The student will be able to give an example
  of sexual selection.

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Section 16-2 Disruption of Genetic Equilibrium

• Requirements of genetic equilibrium
• 1. Mutation
• Genetic equilibrium requires that allele
  frequencies do not change because of mutations.
• Genetic mutations disrupt genetic equilibrium by
  producing new alleles for a trait.
• 2. Migration
• Genetic equilibrium requires that a population
  stays constant.
• Ways to change gene frequencies
• Immigration movement into a population
• Emigration - movement out of a population
• Gene flow - genes move from one population to
  another

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Section 16-2 Disruption of Genetic Equilibrium

• 3. Genetic Drift
• Genetic equilibrium requires the presence of a
  large population.
• Genetic drift is only significant in small and
  medium-sized populations.
• Genetic drift allele frequencies in a
  population change as a result of random events,
  or chance (Figure 16-6, pg 305).
• 4. Nonrandom Mating
• Genetic equilibrium requires random mating,
  regardless of genetic makeup.
• Assortative mating - selection of a mate based on
  similar characteristics.
• Nonrandom mating can affect genotypes, but it
  does not affect overall allele frequencies.

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Section 16-2 Disruption of Genetic Equilibrium

• 5. Natural Selection- Genetic equilibrium
  requires the absence of natural selection.
• Figure 16-7, pg 307!!!
• Stabilizing Selection - individuals with the
  average form of a trait have the highest fitness.
• Directional Selection individuals that display
  a more extreme form of a trait have a greater
  fitness than individuals with an average form of
  the trait.
• Disruptive Selection - individuals with either an
  extreme variation of a trait have a greater
  fitness than individuals with an average form of
  the trait.
• Sexual Selection Females tend to choose the
  males as mates based on certain traits.

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Section 16-3 Formation of Species

• Section 16-3 Objectives
• (1) The student will be able to explain the
  difference between the morphological concept of
  species and the biological species concept.
• (2) The student will be able to define geographic
  isolation, and explain how it can lead to
  speciation.
• (3) The student will be able to name 2 kinds of
  reproductive isolation.
• (4) The student will be able to summarize the
  punctuated equilibrium hypothesis, and contrast
  it with the hypothesis of gradual change.

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Section 16-3 Formation of Species

• The Concept of Species
• Speciation process of species formation
  existing species are changed versions of older
  species results in many related populations
• Morphological Concept of Species
• Morphology the internal external structure
  and appearance of an organism basis for species
  classification
• This concept is limited because there can be
  phenotypic differences among individuals in a
  single population (Figure 16-9, pg 309).
• The Biological Species Concept
• Ernst Mayr, German born/American biologists,
  defined a species as a population of organisms
  that can successfully interbreed but cannot breed
  with other groups.
• Definition does not match extinct organisms or
  ones who reproduce asexually since the
  reproductive abilities cannot be tested.

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Section 16-3 Formation of Species

• Isolating Mechanisms
• Geographic Isolation physical separation of
  individuals in a population, such as when a
  habitat becomes divided.
• Natural selection genetic drift causes 2
  subpopulations to diverge (differ), eventually
  causing mating to not occur
• Reproductive Isolation results from barriers to
  successful breeding between population groups in
  the same area.
• Results in genetic variations
• 2 types of reproductive isolation
• 1. Prezygotic isolation occurs before
  fertilization
• 2. Postzygotic isolation occurs after
  fertilization

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Section 16-3 Formation of Species

• Rates of Speciation
• Fossil record shows that many species existed
  without change for long periods of time.
• Punctuated equilibrium the hypothesis that
  evolution proceeds at an irregular rate, with
  short periods of rapid evolution followed by long
  periods where no evolution occurs.