Chapter 16: Evolution of Populations

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Chapter 16 Evolution of Populations

• 16.1 Genes and Variation
• 16.2 Evolution as Genetic Change
• 16.3 The Process of Speciation

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Population Genetics

• Evolutionary thought today is tightly linked to
  genetics.
• Remember, populations, not individuals evolve.
• All the alleles in a pop. added together are
  called the gene pool??.

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Blue People of Kentucky
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Population Genetics

• The frequency that any one allele is seen in the
  population is called the ?allele frequency
  (relative frequency)?.
• Is the frequency of the dominant Huntingtons
  allele high?
• Is the frequency of
• the dominant allele
• causing 6 fingers high?

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Population Genetics

• If the frequency of the alleles doesnt change
  over time, the population is at genetic
  equilibrium???.
• Hardy-Weinberg Principle
• see page 401

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Population Genetics

• When alleles are brought in and out of a
  population due to migration of individuals, it is
  called gene flow.

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Population Genetics

• When isolated chance events can alter gene
  frequencies in a population (therefore disrupting
  gene equilibrium) you have what is called genetic
  drift.
• Common in small isolated populations such as the
  Amish of Lancaster, PA
• Darwins finches (perhaps)
• founder effect change as a result of migration

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Population Genetics

• Sources of Genetic Variation
• Mutations
• Gene Shuffling
• Single gene trait
• Polygenic trait

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Population Genetics

• ???Types of selection ???
• When natural selection of a trait favors the
  average individuals in the pop. it is called
  stabilizing selection.

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Population Genetics

• ???Types of selection ???

• When natural selection favors both extreme
  phenotypes of a trait in a pop., it is called
  disruptive selection.

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Population Genetics

• ???Types of selection ???

• When natural selection favors one extreme
  phenotype of a trait, it is called directional
  selection.

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Population Genetics

• Type of Selection??
• Grey mice are preyed upon but black and white
  mice are left alone?
• The longer a giraffes neck gets the more food is
  available, while short necked giraffes die of
  starvation before they can reproduce?
• A slow gazelle is easily caught by a cheetah, but
  one too fast breaks its legs easily and is eaten
  by hyenas??

Disruptive
Directional
Stabilizng
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Population Genetics

• Artificial Selection Selection for traits that
  are determined and monitored by man.
• Ex. Breeding animals such as dogs or cats.
• Sexual Selection Selection by one gender for
  another gender.
• Ex. Peacock feathers, body hair disappearance in
  humans, walrus tusks.

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Speciation

• ???Speciation is when a new species is formed.
  This means that the individuals in the new
  species can no longer produce successful
  offspring with the population from which they
  came.

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Speciation

• ???Geographic Isolation can cause speciation over
  long periods of time.
• The seperated organisms are adapting to different
  environments and responding differently.
• Eventually if a mating is attempted, they can no
  longer produce successful offspring with one
  another.

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Speciation

• Reproductive Isolation is when a population can
  no longer successfully interbreed with its parent
  population (the pop. it came from).
• Reproduction if attempted will fail.
• Ex. One group breeds
• in the fall, one in the
• spring and over time
• the populations become
• new species incapable
• of interbreeding.
• Mating Calls
• Courtship rituals differ

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Speciation

• Temporal Isolation
• Two or more species reproduce at different times
• Example orchid in the rainforest

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Speciation

• Changes in chromosome number can cause
  speciation.
• Some cases of polyploidy (more common in plants)
  produce individuals that can only mate with other
  polyploids in a pop.

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17.4 Speciation

• Can occur rapidly
• Punctuated Equilibrium
• Gould
• Can occur very slowly
• Gradualism
• Darwin
• see page 439

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17.4 Patterns of Evolution

• ???Adaptive Radiation When an ancestral species
  evolves into several different species, each
  filling a specific niche.
• Darwins finches
• Hawaiian Honeycreepers
• (p. 406 436).

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17.4 Patterns of Evolution

• Divergent Evolution Species that once were
  similar or closely related become very different.
• New Species are very different from each other.
• Ex. Adaptive Radiation

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17.4 Patterns of Evolution

• ???Convergent Evolution Unrelated species that
  live in similar environments evolve the same
  adaptations in order to survive.
• Ex. Tasmanian Wolf and North American Wolf.
• P. 437

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Patterns of Evolution

• Coevolution the process by which two species
  evolve in response to changes in each other over
  time.
• Example flowering plants and their pollinator
• Page 437

http//biology.clc.uc.edu/courses/bio303/coevoluti
on.htm
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17.4 Note

• ???Common genetic occurrences we have studied
  such as polyploidy, crossing over, and point
  mutations can provide the genetic basis for
  evolution. Although these genetic changes are
  not evolution themselves, they can begin the long
  process of evolution by affecting one individual
  in a population in a positive way. But only if
  the trait is passed on, and on, and on???