Zoology Unit 2

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• Zoology Unit 2
• Evolution the change in a population over time.

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• Pre-Darwin Ideas
• 1. Lamarck
• A. French zoologist

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• Thought organisms developed new organs or
  modified existing organs to adapt to new
  situations.
• Organs not used would degenerate.

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• Species did not become extinct, only evolved
  into new species.
• Giraffes Thought they got long necks by
  stretching to get to higher leaves.

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• Wrong because modifications like that cannot be
  passed to the next generation.

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• 2. Darwins Ideas
• A. Thought species changed over long periods of
  time. (too long)

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• B. Theory of Uniformitarianism (Charles Lyell)
  said the earth was very old and the earth changed
  over time. This idea reinforced Darwins idea.

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• C. From looking at fossils on South America he
  recognized that some animals become extinct
  without leaving descendents or becoming new
  species.

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• D. On Galapagos he observed finches and
  tortoises.
• E. The finches have different size beaks with
  different shapes. Depending on what they eat.
  They show adaptive radiation.

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• Adaptive radiation is the formation of new forms
  of a species from an ancestral species in
  response to the opening of new habitats.

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• F. Natural selection developed after reading
  Thomas Malthus. He said human population will
  continue to grow until stopped by some factor
  such as war, famine, disease, etc.

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• Darwin thought the same thing might happen in
  nature.

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• G. Natural Selection has 4 parts.
• 1. All organisms produce more offspring than can
  reproduce.

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• 2. Inherited variation exists. Variations come
  from mutations in DNA and random mating. Some may
  be advantageous, some may be harmful.

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• 3. Individuals with the advantageous traits are
  more likely to survive and pass them to the next
  generation. These are called adaptive traits.

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• 4. Adaptive traits are passed on and become more
  frequently seen in the population. Traits that
  are dis-advantageous to the individual will
  eventually be eliminated.

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• 3. MICRO and MACRO EVOLUTION
• A. Microevolution is a change in the frequency of
  alleles in a population over time.

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• Examples are drug resistant strains of bacteria
  and bug that are resistant to pesticides.

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• B. Macroevolution is the large scale changes that
  result in extinction and the formation of new
  species.

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• C. What scientists refer to as evidence for
  macroevolution.
• 1. Biogeography is the study of the geographic
  distribution of plants and animals.

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• Biogeographers try to explain
• Why similar animals end up in places that are not
  connected physically. Ex. cats

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• Why animals separated by geographical barriers
  are often very different in spite of similar
  environmental conditions. Ex Australia and New
  Zealand.

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• 2. Paleontology the study of fossil records.
  Older fossils are usually found below or deeper
  than new fossils. By looking at how fossils
  change from older layers to newer layers we see
  how animals have changed.

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• 3. Comparative Anatomy
• Convergent evolution occurs when we find
  superficially similar structures in unrelated
  organisms.
• Ex wings in birds and insects.

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• In this case the wings are
  said to be analogous
  structures.

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• Comparative anatomy is the study of living and
  fossilized animals and their relationships.

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• In comparative anatomy homologous structures are
  studied. These are structures in different
  animals that suggests they have a common ancestor.

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• Ex. bones in the forelimbs of birds, humans,
  lizards, bats, etc. as seen in figure 4.11 on
  page 62.

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• Homologous DNA molecules related animals have
  similar DNA derived from the ancestral DNA.

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• 4. Developmental Patterns
• By looking at early embryonic stages we can see
  similarities. From the embryonic stage organisms
  begin to develop differently.

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• This is due to genes that control how fast the
  bones and organs develop and how they are
  proportioned.

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• Phylogeny Scientists use evolutionary evidence
  to build a phylogentic tree. Phylogeny refers to
  the evolutionary relationships of modern
  descendents of a common ancestor.

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• The tree shows the relationship between
  organisms, the branches show where species
  diverged into separate species.

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• DNA (get it?)

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• A. Population and Gene Pool
• 1. A population is a group of individuals of the
  SAME species that occupy an area at the same time.

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• Within the population the individuals will all
  have the same kind of genes. Differences seen in
  individuals is due to the presence of different
  alleles.

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• All the alleles for traits in all traits in a
  population is called the gene pool. It is a pool
  of hereditary resources containing all the
  possible alleles an individual can be made from.

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• 2. Population genetics is the study of the
  genetic events in the gene pool. The
  Hardy-Weinberg theorem describes what happens to
  the frequency of alleles in a population over
  time.

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• The Hardy-Weinberg theorem says if certain things
  (assumptions) are met no evolution will take
  place and the frequency of alleles will not
  change in future generations.

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• What are these assumptions that must be met to
  prevent evolution? There are four.

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• First The population size must be large.
• Second Mating between individuals must be
  random. Natural selection must take place.

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• Third Individuals cannot move into or out of
  the population. This keeps new alleles from
  entering the gene pool.

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• Fourth No new types of alleles are introduced
  due to mutation.

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• It is very unusual for all these assumptions to
  be met so most populations are evolving.

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• B. Evolutionary Mechanisms
• Things that can happen when the Hardy-Weinberg
  assumptions are not met.

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• 1. Sometimes individuals meet and reproduce by
  chance. No natural selection is involved.

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• When this changes the frequency of alleles in a
  population it is called genetic drift .

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• 2. Genetic drift is most likely to occur in
  small populations.

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• 3. The Founder Effect is an example of genetic
  drift. This occurs when a very few individuals
  from a large population colonize a new
  environment away from the parent population.

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• The new colony will only contain the genetic
  make-up of the individuals that founded the new
  colony.

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• 4. Another type of genetic drift is the
  Bottleneck Effect. This occurs when an event
  drastically reduces the size of a population.

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• The remaining population may grow to its original
  size but it will not have the same genetic
  diversity.

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C Z N MKIOGC
R H T Y D P Y G
R N G Z G P H R H N Z G P P G Z H
R N Z G H N P R H N Z P Z H P
O I K M N Z C
G Y P T H R C
R H N Z G P
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• Most biologist believe genetic diversity is
  important to a species survivability. This is
  because a population with high genetic diversity
  will allow it to survive environmental changes.

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• 5. Gene Flow The Hardy-Weinberg theorem assumes
  no immigration or emigration. If it does occur
  there will be a change in the number of alleles
  and the kinds of alleles in a population.

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• 6. Mutation mutations are the origin of new
  alleles and variations. These may help the
  organism become better adapted to their
  environment. Or not.

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• C. SPECIES AND SPECIATION
• 1. A species is a group of populations in which
  genes are actually or potentially exchanged
  through successful interbreeding.

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• 2. Speciation is the formation of new species.
  This can occur in different ways such a
  reproductive isolation.

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• One type of reproductive isolation is PREMATING
  ISOLATION. This is when something prevents mating
  from occurring. This may be a a barrier like a
  river or mountain, or it may be behavioral.

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• Another type is POSTMATING ISOLATION. This occurs
  when successful fertilization and development
  does not happen after mating. The chromosomes may
  not line up properly, etc.

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• 4. Allopatric speciation occurs when a population
  becomes geographically separated from one
  another. They eventually become so different that
  breeding is not possible even if they are
  reunited.

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• They become two separate species.
• 5. Parapatric speciation occurs in small, local
  populations called demes.

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• This is basically the same as allopatric
  speciation only on a smaller scale.

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• C. Rates of Evolution
• 1. Phylogentic gradualism in this model changes
  are gradual over long periods of time.

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• 2. Punctuated equilibrium in this model there
  are long periods of stasis then rapid periods of
  change. The sudden and rapid change may be due to
  environmental changes (like climate change).

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