Speciation

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Speciation

• Genetic Equilibrium
• Disruption of Genetic Equilibrium
• Formation of Species

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Genetic Equilibrium
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• Species a group of individuals that look similar
  and whose members are capable of producing
  fertile offspring in the natural environment

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Morphological Species Concept

• Morphological Species Concept the idea that
  organisms can be classified by differences in
  their appearance
• Using this concept, scientists can readily
  communicate about the characteristics, behavior,
  and relationships of organisms.
• The morphological concept of species is limited
  because it does not account for the reproductive
  compatibility of morphologically different
  organisms.

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Biological Species Concept

• Biological Species Concept the idea that
  organisms can be classified by their ability to
  breed with one another
• Using both the biological and morphological
  concepts of species, modern scientists have
  arrived at the current definition of the term
  species.

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• Species a group of individuals that look
  similar and whose members are capable of
  producing fertile offspring in the natural
  environment

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Variation of Traits in a Population

• Population all the members of a species that
  live in the same area and make up a breeding
  group
• Within a population, individuals vary in many
  observable traits.

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Caribou Population Distribution
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Variation is the Raw Material of Natural Selection
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Variation of Traits in a Population
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What causes variation in traits?

• Environmental Factors
• Heredity
• A difference in genotype usually results in a
  difference in phenotype.
• Variations in genotypes arise through
• Mutation
• Genetic Recombination
• Independent Assortment
• Crossing Over

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Allele Frequencies and Genetic Equilibrium

• Gene Pool all the genes for all the traits in a
  population
• Allele Frequency the percentage of an allele in
  a gene pool
• Genetic Equilibrium the condition in which
  allele frequencies in a population do not change
  from generation to generation

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Genotypic and Allele Frequencies
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Hardy Weinberg

• Hardy and Weinberg outlined the conditions
  necessary for genetic equilibrium.

Wilhelm Weinberg
Godfrey Hardy
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Hardy-Weinberg Principle

• Hardy and Weinberg outlined the conditions
  necessary for genetic equilibrium.
• 1. no mutations occur
• 2. individuals neither enter nor leave the
  population through migration
• 3. the population is large
• 4. individuals mate randomly
• 5. natural selection does not occur

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Hardy-Weinberg Principle

• If one of these conditions does not hold true,
  allele frequencies of the population may change.
  In other words, evolution will occur.

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Disruption of Genetic Equilibrium
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Disruption of Genetic Equilibrium

• Evolution occurs when genetic equilibrium is
  disrupted.

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1. Mutation

• Mutations affect genetic equilibrium by producing
  totally new alleles for a trait.
• In addition, mutations can change the frequency
  of the alleles already present in the gene pool.
• The occurrence of mutation in most alleles is too
  low to cause major changes in the allele
  frequencies of an entire population.

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1. Mutation
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2. Migration

• Migration the movement of individual organisms
  into or out of a population, community, or biome
• Immigration movement of new individuals into a
  population
• Emigration departure of individuals from a
  population
• Gene Flow the movement of genes into or out of a
  population

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2. Migration
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3. Genetic Drift

• Genetic Drift a shift in allele frequencies in a
  population due to random events or chance
• In small populations, chance can significantly
  affect allele frequencies from one generation to
  the next.

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3. Genetic Drift
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3. Genetic Drift
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4. Non-Random Mating

• If animals chose their mates then certain traits
  would be selected for over less desirable ones.

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5. Natural Selection

• Natural selection is an ongoing process in
  nature, and is the single most significant factor
  disrupting genetic equilibrium.

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4 Types of Natural Selection

1. Stabilizing Selection
2. Directional Selection
3. Disruptive Selection
4. Sexual Selection

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Stabilizing Selection

• Stabilizing Selection a type of natural
  selection in which the average form of a trait
  causes an organism to have an advantage in
  survival and reproduction
• The extreme forms of the trait confer a
  disadvantage to the organism.
• Stabilizing selection is most effective in a
  population that has become well adapted to its
  environment.
• Stabilizing selection is the most common type of
  NS.

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Directional Selection

• Directional Selection a type of natural
  selection in which the distribution of a trait is
  shifted toward one of the extremes

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Disruptive Selection

• Disruptive Selection natural selection in which
  individuals with either of the extreme forms of a
  trait have an advantage in terms of survival and
  reproduction
• The average form of the trait confers a selective
  disadvantage to the organism.

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Sexual Selection

• Sexual Selection the preferential choice of a
  mate based on the presence of a specific trait
• Sexual selection may be stabilizing, directional,
  or disruptive.

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Formation of Species
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Speciation

• Disruption of genetic equilibrium leads to
  changes in the gene pool of a population.
• Natural selection causes the most significant
  genetic changes in a population, however, such
  changes do not necessarily lead to speciation.
• Speciation the formation of a new species

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Speciation
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Speciation
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Isolated Populations

• For a new species to arise, interbreeding of the
  population of fertile offspring must somehow
  cease among members of a formerly successful
  breeding population.
• For this to occur, populations or segments of
  populations must somehow become isolated.
• Two Forms of Isolation
• Geographic Isolation
• Reproductive Isolation

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Geographic Isolation

• Geographic Isolation the physical separation of
  populations
• Examples population becomes divided by land or
  water barrier, colonization of new island, river
  changes course, highway built across field, etc.

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Reproductive Isolation

• Reproductive Isolation the inability of formerly
  interbreeding organisms to produce offspring
• Reproductive isolation can occur through
  disruptive selection.

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Rates of Speciation

• Punctuated Equilibrium a theory that speciation
  may occur during brief periods of rapid genetic
  change
• Gradualism a theory that speciation may occur
  through a gradual change of adaptations
• Extinct the state of a species that no longer
  exists
• For a species to continue to exist, some members
  must have traits that allow them to survive and
  pass their genes on to the next generation.

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