Evolution

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Evolution

• change over time

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The Theory of Evolution

• What is a theory?
• A well supported, testable explanation of
  phenomena of the natural world
• http//www.teachersdomain.org/resource/evol07.sci.
  life.gen.theorydef/
• What is the Theory of Evolution?

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The Theory of Evolution

• Evolution is change in a population over time.
• As the environment changes, species either adapt
  or go extinct.
• Adaptation an inherited characteristic that
  increases an organisms chance of survival.

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Common Beliefs during Darwins Time

• Many believed that Earth was only a few thousand
  years old. In addition, most people believed
  that neither the planet nor the species that
  inhabited it had changed since the beginning of
  time.

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Challenges to Common Beliefs

• During Darwins time, many fossils were being
  discovered which challenged the notion that
  plants and animals had not changes since Earth
  was formed.

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Hutton and Lyell

• The work of James Hutton and Charles Lyell helped
  scientists recognize that Earth is many millions
  of years old and the processes that changed the
  Earth in the past are the same ones that change
  the Earth today.

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HuttonUniformitarianism

• The past history of our globe must be explained
  by what can be seen to be happening now. No
  powers are to be employed that are not natural to
  the globe, no action to be admitted except those
  of which we know the principle. James Hutton

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Charles Lyell

• The work of Charles Lyell which was well known to
  Charles Darwin provided principles and rules for
  how Earth formed over time.
• Law of Superposition
• Principle of Original Horizontality
• Law of Crosscutting Relationships

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Geologic Time

• Evidence showed that the Earth was much older
  than the biblical account.
• For the changes on the Earth to happen by natural
  processes the Earth had to be very old.
• Modern relative and absolute dating techniques
  estimate the age of the Earth at 4.6 billion
  years.
• Life can be dated back to about 3.8 billion
  years.
• Write on your bellwork paper three methods for
  finding the age of the Earth.

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Age of the Earth

• Relative dating techniques
• Rates of Erosion
• Pollen Analysis
• Varve Count
• Cultural Affiliation
• Seriation

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Age of the EarthAbsolute dating techniques
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The Fossil Record

• Fossils are the remains of animals or plants that
  lived in a previous geologic time.
• Fossils can be used to find both the relative and
  absolute age of the rock, plant or animal.
• Fossils provide clues to the past geologic
  events, climates and the evolution of living
  things.
• Fossil Life An Introduction

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Earlier Concepts of Evolution

• Charles Darwin and Alfred Russell Wallace were
  not the first to propose the idea that species
  evolved over time.
• The difference was that earlier theories did not
  propose a mechanism for how evolution occurred.
• The breakthrough for Darwin and Wallace was not
  the theory of evolution. It was the theory of
  evolution by natural selection.

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Jean-Baptiste Lamarck

• Argued that organisms acquire or lose certain
  traits during their lifetime by use or disuse.
• He thought that these traits could then be
  passed on to offspring. Over time this would
  cause change in a species.

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Charles Darwin

• Darwin was influenced by the work of Thomas
  Malthus. Malthus argued that if the human
  population continued to grow at high rates,
  sooner or later there wouldnt be enough space
  and food for everyone.
• Darwin reasoned that this should apply to all
  organisms. He began to consider why some survive
  and others do not.

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Charles Darwin

• Traveled around the world on the HMS Beagle,
  collecting fossils and specimens of organisms
  that he found living in different environments.
  He was astonished at the amount of diversity he
  found among organisms in different environments.

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Charles Darwin

• He made many important observations on the
  Galapagos Islands.

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Galapagos Islands

• The Galapagos islands are a province of the
  Republic of Ecuador.
• They lie in the Pacific Ocean about 1,000 km from
  the South American coast.
• The islands straddle the equator.
• There are 13 large islands, 6 smaller ones and
  107 islets and rocks.

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The Galapagos

• Darwin noticed that the shape of turtle shells
  was different for each island.

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The Galapagos

• The finches on each island had different types of
  beaks. Darwin reasoned that the finches had
  adapted beaks that were well suited to eat the
  type of food available on their island.

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• Darwin hypothesized that these finches had
  started as one species, but had adapted to the
  environments of each island over large periods of
  time.
• He developed the
• theory of natural
• selection.

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What is a Species

• This question is not so easily answered.
• The biological species concept states that
  species are organisms that are reproductively
  isolated from each other.
• According to this definition, the same kind of
  organism is in the same species if it would
  interbreed if given the opportunity.

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Interbreed

• Interbreed means that two organisms of the same
  species can give birth to progeny
• AND
• Their progeny can survive and give birth to
  progeny.
• Therefore, to be a species, the progeny must be
  viable not sterile.

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Mule

• For example a horse and donkey can breed but they
  will produce a sterile mule.

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Species ?

• The problem is that some organisms that no-one
  would consider the same species can reproduce and
  give birth to offspring that are either partially
  or fully viable.

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The Species Problem

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Natural Selection

• Species change over time because of changes in
  the environment (selection pressures)
• Natural Selection Those adapted to the
  environment are more likely to survive and pass
  their genes to the next generation, while those
  not well suited do not survive or leave fewer
  offspring.

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Natural Selection

• Struggle for existence members of a species
  compete for food, space, and other necessities
• Survival of the Fittest adaptations that make an
  organism better suited for its environment help
  them survive and reproduce.

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• Over time, natural selection causes a change in
  the characteristics of a population (adaptations)

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• Populations Evolve, Individuals Do Not!!!!

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• Darwin suspected that all species present on
  earth had begun as one species, and through a
  series of adaptations over millions of years, had
  diverged into all the species present today.
• Descent with Modification through a series of
  adaptations, each new species arises from another.

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The Origin of Species

• He published his theory of natural selection in
  1859, many many years after he had come up with
  the theory.

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The Peppered Moth

• There must be genetic variation in order for
  natural selection to occur. There are two forms
  of the peppered moth prevalent in England.

carbonaria
typica
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Peppered Moths

• The lighter colored moth is more difficult to
  spot against typical tree bark, while the darker
  moth stands out and makes easier prey.

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Peppered Moths

• At the beginning of the industrial revolution in
  England, coal burning produced soot that covered
  the countryside of some areas.

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Peppered Moths

• Now the white moths stand out, while the black
  moths are hard to see. The black moths are more
  likely to survive and pass on the genes for dark
  color to offspring. Over time, the black moths
  became more common than the white moths.

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• Populations Evolve, Individuals Do Not!!!!

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• Contrast how Lamarck and Darwin would each
  explain the evolution of the giraffe.

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Evidence for Evolution
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Evidence

• Fossil Record
• Geographic Distribution of Living Species
• Homologous Structures of Living Organisms
• Vestigial Structures
• Similarities in Embryology
• Molecular Biology

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Fossil Record

• By comparing fossils from older rock layers with
  fossils from younger rock layers, scientists can
  see how life on Earth has changed over time.
• Hundreds of transitional fossils have been found
  which show intermediate stages of evolution of
  modern species from species now extinct
• this is an incomplete record with many gaps

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Evolution of the Horse
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Geographic Distribution of Living Species

• Species living in different places with similar
  environments have similar anatomies and
  behaviors, even though they are unrelated
• They are exposed to similar pressures of natural
  selection so they evolve similar characteristics

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Homologous Body Structures

• Homologous develops from the same part of the
  embryo but have a different forms and functions
  (modified between groups)
• Analogous parts with similar functions which
  develop from different parts of the embryo
  (similar function, different structure)
• (embryo is the early stage of development)

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Homologous Body Structures
http//evolution.berkeley.edu/evolibrary/home.php
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Homologous Body Structures

• Helps biologists group animals according to how
  recently they shared a common ancestor
• Dolphins look more like fish but their homologies
  show they are mammals. They have lungs rather
  than gills and obtain oxygen from air, not water.
  (evolved from land mammals, not fish)
• Phylogenetic trees show evolutionary relationships

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Phylogenetic Tree
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Vestigial organs

• Organs so reduced in size that they no longer
  serve the function of homologous organs in
  related species
• The presence of the organ does not affect its
  ability to survive and reproduce, so natural
  selection does not eliminate it

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Vestigial Structures

• Examples wings on flightless birds, human coccyx
  and appendix

The appendix, for instance, is believed to be a
remnant of a larger, plant-digesting structure
found in our ancestors.
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Similarities in Embryology

• All embryos develop similarly
• Similar genes that define their basic body plan
• Tails as embryos
• Embryos of all vertebrates especially similar
  same groups of cells develop in same order and in
  similar patterns (homologous structures)

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Molecular Biology

• All organisms use DNA and RNA to transmit genetic
  information
• ATP is an energy carrier in all organisms.
• You can compare the similar amino acid sequences
  (i.e. proteins)

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Evolution

• Origin of Life and Speciation

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What is Natural Selection?

• Who came up with the theory of natural selection?
• Name some criteria necessary for natural
  selection to occur.

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Name types of evidence for evolution.

• Fossil record
• Homologous structures
• Vestigial structures
• Embryonic structures
• Molecular record

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What do we mean by survival of the fittest? Give
some examples.
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Origin of Life

• We have said that all organisms have ancestors,
  but not all organisms have descendants. What do
  we mean by that?
• What about the first organism? How do you think
  life first began on Earth?

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Origin of Life

• What do you think the first organism was like?

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Early Earth

• Early Earth was formed about 4.6 billion years
  ago and was very different than earth today.
• How do you think it might have been different?

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Early Earth

• The atmosphere was very different than it is now,
  containing little or no oxygen.
• Earth was too hot for liquid water.
• Once the surface cooled enough for rocks to form,
  the surface was covered with volcanic activity.

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Early Earth

• About 3.8 billion years ago the Earth cooled
  enough for liquid water to remain.
• Thunderstorms drenched the planet and oceans
  covered most of the surface.

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Could organic molecules have evolved under these
conditions?

• In the 1950s Stanley Miller and Harold Urey
  tried to simulate the conditions of early Earth.
  
• They showed how several amino acids could be
  created under those conditions.

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Miller and Ureys Experiment

• They passed sparks (representing lightening)
  through a mixture of hydrogen, methane, ammonia,
  and water (representing the atmosphere)

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The Big Picture

• Miller and Urey showed that the mixtures of
  organic compounds necessary for life could have
  arisen on primitive earth!

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Hypothesis of the Origin of Life

• The leap from a mixture of organic molecules to a
  living cell is large.
• Tiny bubbles of organic molecules (called
  proteinoid spheres) have characteristics of
  living systems such as selectively permeable
  membranes and means of storing and releasing
  energy. They may have become more and more like
  living cells over time.

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Hypothesis of the Origin of Life

• Experiments have shown that under the conditions
  of early Earth, small RNA sequences could have
  formed and replicated on their own. This could
  have created a simple RNA-based form of life from
  which the DNA system could have evolved.

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Hypothesis of Origin of Life

• How certain do you think this hypothesis is? Do
  you think it will ever be changed? Do you think
  it will be changed during your lifetime?

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Origin of Life

• Evidence indicates that about 200-300 million
  years after the accumulation of liquid water on
  Earth, cells similar to modern bacteria were
  common.

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Changing Earth

• Photosynthetic bacteria became common and oxygen
  began to accumulate in the atmosphere and the
  ozone layer formed.
• The rise in oxygen caused some life forms to go
  extinct, while others evolved ways to use oxygen
  for respiration.

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Hypothesis of Origin of Eukaryotic
Cells-Endosymbiotic Theory

• What is a eukaryotic cell?
• Prokaryotic cells began to evolve internal cell
  membranes- this was the ancestor to eukaryotic
  cells.
• Smaller prokaryotes began living inside this
  ancestor and over time it became an
  interdependent relationship. What does this mean?

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Lynn Margulis Endosymbiotic Theory

• One group which entered the cell had the ability
  to use oxygen to generate ATP. These evolved
  into mitochondria.
• Another group of prokaryotes which carried out
  photosynthesis evolved into chloroplasts.

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Evidence for Endosymbiotic Theory

• Mitochondria and chloroplasts have many
  characteristics of free living bacteria
• 1- contain DNA similar to bacterial DNA
• 2- have ribosomes of similar size and structure
  to those of bacteria
• 3- reproduce by binary fission like bacteria

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Any Questions?
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Speciation

• Speciation the formation of new species
• What is a species?
• As new species evolve, the populations become
  reproductively isolated from each other. (cannot
  interbreed and produce fertile offspring)

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How could speciation occur?
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Isolating Mechanisms

• Behavioral Isolation differences in courtship or
  reproductive strategies that prevent breeding
• Geographic Isolation populations separated by
  physical barriers
• Temporal Isolation reproduce at different times

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Geographic Isolation
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Patterns of Evolution

• Adaptive Radiation when a species evolves into
  several different forms
  that live in different ways
• Can you think of an
  example we have discussed, or any other
  example, of adaptive radiation?

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Patterns of Evolution

• Example of adaptive radiation Darwins
  finches-more than a dozen species evolved from a
  single species

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Patterns of Evolution

• Convergent Evolution unrelated organisms come to
  resemble one another due to similar selective
  pressures
• Example?
• What is divergent evolution?

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Divergent Evolution

• occurs when two or more biological
  characteristics have a common evolutionary origin
  but have diverged over evolutionary time. This is
  also known as adaptation or adaptive evolution.
• example, the vertebrate limb is one example of
  divergent evolution. The limb in many different
  species has a common origin, but has diverged
  somewhat in overall structure and function.

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• Structures that are similar due to evolutionary
  origin, such as the forearm bones of humans,
  birds, porpoises, and elephants, are called
  homologous. Structures that evolve separately to
  perform a similar function are analogous. The
  wings of birds, bats, and insects, for example,
  have different embryological origins but are all
  designed for flight.

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Patterns of Evolution

• Coevolution when two species evolve together, in
  response to changes in each other
• Can you think of an example?

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Coevolution

• Example flowers and pollinators, flowers and
  plant-eating insects

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Gradual versus Punctuated Evolution

• Gradual slow and steady change
• Punctuated long, stabile periods interrupted by
  brief periods of rapid change

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Any Questions?
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Can we see evolution occur?

• Can you think of an example of an organism that
  evolves quickly? One that has evolved during
  your life time?

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Bacterial EvolutionWhat allows bacteria to
evolve so quickly?
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Insect Evolution
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Population Genetics

• The study of traits and changes in populations.

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Gene Pool

• All mechanisms of evolution involve changes in
  the gene pool.
• A gene pool is the combined genetic material of
  all the members of a given population.

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Microevolution

• The change in a populations alleles over a
  period of time.
• These changes manifest themselves in the
  organisms phenotype.
• Since individuals do not evolve, a population
  must be watched to detect any change in genetic
  modification.

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Allelic Frequencies

• The number of each allele is a fraction of all
  the genes for a particular trait.
• These fractions are known as allelic frequencies.
• The constant state of allele frequencies is
  called genetic equilibrium.

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Hardy-Weinberg Principle

• Developed to determine if a population is
  evolving.
• Authors of the theorem set up parameters, which
  do not exist in nature, to be followed when
  determining the allele frequencies of any
  population

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Hardy Weinberg conditions

• The population must be very large in size.
• It must be isolated from other populations (no
  gene flow)
• No mutations
• Random mating
• No natural selection

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Mathematical Wedding of Mendel and Darwin The
Hardy Weinberg Theorem

• pq 1
• p2 2pq q2 1
• p represents the frequency of the dominant allele
• q represents the frequency of the recessive
  allele
• p2 represents the frequency of the homozygous
  dominant phenotype
• 2pq represents the frequency of the heterozygous
  phenotype
• q2 represents the frequency of the homozygous
  recessive phenotype

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Hardy Weinberg Problems
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Causes for Microevolution

• Genetic Drift The random change in gene pools
  due to random events.
• Examples migrations, natural disasters,
  isolation
• Bottleneck effect genetic drift occurring after
  a random population reducing event
• Founders effect the effect of establishing a
  new population by a small number of individuals,
  carrying only a small fraction of the original
  population's genetic variation.
• As a result, the new population may be
  distinctively different, both genetically and
  phenotypically, from the parent population from
  which it is derived.
• In extreme cases, the founder effect is thought
  to lead to the speciation and subsequent
  evolution of new species.

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Genetic Drift and the Founder Effect

• Polydactyly -- extra fingers or sometimes toes --
  is one symptom of Ellis-van Creveld syndrome.
• The syndrome is commonly found among the Old
  Order Amish of Pennsylvania, a population that
  experiences the "founder effect."
• Genetically inherited diseases like Ellis-van
  Creveld are more concentrated among the Amish
  because they marry within their own community,
  which prevents new genetic variation from
  entering the population.

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Causes for Microevolution

• Gene Flow
• The movement of alleles into and out of a
  population
• Migration of an organism into different areas can
  cause allelic frequency changes
• Immigration
• Emigration

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Causes for Microevolution

• Mutations
• These change the genome of an organism and are an
  important source of natural selection

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Causes for Microevolution

• Nonrandom Mating
• Natural Selection
• Those individuals who leave behind more
  offspring, pass on more of their alleles and have
  a better success rate in dominating the
  population.

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Normal Distribution

• Most common in nature
• Bell-shaped curve

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Directional Selection

• A change in the environment favors an extreme
  phenotype

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Examples of Directional Selection

• Evolution in horse limb morphology illustrates
  directional selection-- over time, natural
  selection favored individuals with limbs adapted
  for running on open grassland areas.
• Yet another soon-to-be-classic example of
  directional selection at work antibiotic
  resistance in bacteria.

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Disruptive Selection

• An environmental change makes it unfavorable to
  have the medium phenotype
• Batesian mimicry gives an example of disruptive
  selection. Some places in Africa have three
  species of bad tasting butterflies. Different
  females of edible swallowtail butterflies mimic
  each of the distasteful species.

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Class Activity Fishy Frequencies(or How
Selection Affects the Hardy-Weinberg Equilibrium)

• Introduction
• Understanding natural selection can be confusing
  and difficult. People often think that animals
  consciously adapt to their environments - that
  the peppered moth can change its color, the
  giraffe can permanently stretch its neck, the
  polar bear can turn itself white - all so that
  they can better survive in their environments.
• In this lab you will use fish crackers to help
  further your understanding of natural selection
  and the role of genetics and gene frequencies in
  evolution.

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Background Facts about the 'Fish'

• These little fish are the natural prey of the
  terrible fish-eating sharks - YOU!
• Fish come with two phenotypes of gold and brown
• gold this is a recessive trait (f) these fish
  taste yummy and are easy to catch.
• brown this is a dominant trait (F) these fish
  taste salty, are sneaky and hard to catch.
• You, the terrible fish-eating sharks, much prefer
  to eat the yummy gold fish you eat ONLY gold
  fish unless none are available in which case you
  resort to eating brown fish in order to stay
  alive.
• New fish are born every 'year' the birth rate
  equals the death rate. You simulate births by
  reaching into the container of 'spare fish' and
  selecting randomly.
• Since the gold trait is recessive, the gold fish
  are homozygous recessive (ff). Because the brown
  trait is dominant, the brown fish are either
  homozygous or heterozygous dominant (FF or Ff).

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Hardy-Weinberg

• For fish crackers, you assume that in the total
  population, you have the following genotypes, FF,
  Ff, and ff. You also assume that mating is random
  so that ff could mate with ff, Ff, or FF or Ff
  could mate with ff, Ff, or FF, etc. In addition,
  you assume that for the gold and brown traits
  there are only two alleles in the population - F
  and f. If you counted all the alleles for these
  traits, the fraction of 'f' alleles plus the
  fraction of 'F' alleles would add up to 1.
• The Hardy-Weinberg equation states that p2 2pq
  q2 1
• This means that the fraction of pp (or FF)
  individuals plus the fraction of pq (or Ff)
  individuals plus the fraction of qq (ff)
  individuals equals 1. The pq is multiplied by 2
  because there are two ways to get that
  combination. You can get F from the male and f
  from the female OR f from the male and F from
  female.
• If you know that you have 16 recessive fish
  (ff), then your qq or q2 value is .16 and q the
  square root of .16 or .4 thus the frequency of
  your f allele is .4 and since the sum of the f
  and F alleles must be 1, the frequency of your F
  allele must be .6 Using Hardy Weinberg, you can
  assume that in your population you have .36 FF
  (.6 x .6) and .48 Ff (2 x .4 x .6) as well as the
  original .16 ff that you counted.