MEASURING EVOLUTION

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MEASURING EVOLUTION
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When is it Called Evolution?
Microevolution Changing Allele Frequencies in
Populations

• Macroevolution Speciation

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Lets ask an important question
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Can Reebops evolve?

• Why do you think they could or could not?
• What are some of the conditions that might cause
  Reebops to evolve?
• How would you know if they did evolve?

Write questions and answers in your notebook/
Pair/Share
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Consider the Scenario

• A drought has forced the Reebop population to
  move to a new location
• The vegetation in this new location is not as
  tall as in their old location
• The tails of straight-tailed Reebops stick up
  above the vegetation making them more visible to
  predators (uh-oh)
• All straight-tailed Reebops are eaten before they
  can reproduce.

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How Can We Find out if Reebops Evolve Under These
Selection Pressures?

• Set up a scientific inquiry.
• Gather data
• Interpret data

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What data/information do we need to answer our
question?

• The answer is in the definition of EVOLUTION
• EVOLUTION A process that occurs over many
  generations that results in heritable changes in
  a population.
• Heritable changes

Gene/allele frequency
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How Can We Measure Whether Evolution Has Occurred
in Reebops?

• Look at changes in gene frequency
• Remember the Reebops
• tail alleles T (curly), t (straight)
• Parents were heterozygous (Tt) for this gene
• What percentage of parent gene pool was T
• What percentage of parent gene pool was t

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Set up our scientific inquiry

• What does gene pool look like after 1 generation
  without any natural selection?
• What does gene pool look like after 1 generation
  in the low vegetation habitat?
• Is there a control group here???
• How can this information tell us if natural
  selection has occurred?

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Use our Punnett Square to tell us about gene
frequencies after 1 generation

• Parents Tt x Tt 100 offspring

25 TT offspring
50Tt offspring
25 tt offspring
T allele? t allele?
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• Allele Frequency of parents
• 50 T
• 50 t
• Allele Frequency after 1 generation
• 50 T
• 50 t
• Was there a change in allele frequency?
• Did evolution occur in our population with out
  selection?

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Now its your turn Do the Natural Selection
Experiment with Reebops

• (a 5 generation experiment)

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Did Evolution Occur 5 Generations After the
Reebops Moved?

• What was the allele frequency for T?
• What was the allele frequency for t?
• How do they compare to the parent allele
  frequency?

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Sample DataDid Our Reebop Population Evolve?
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Use our Punnett Square to tell us about gene
frequencies after 5 generations
TT (.5 x .5) .25 Tt 2(.5 x .5) .5 tt
(.5 x .5) .25
TT (.73 x .73) Tt 2(.73 x .27) tt
(.27 x .27) .
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Think About This

• If selection pressure against tt (straight tail )
  continues, will the t allele ever disappear from
  the population?

• If there is no selection pressure against Tt,
  will the t allele disappear from the population
  or persist?

Write questions and answers in your notebook/
Pair/Share
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Natural Selection Doesnt Always Select the
Same Way

• (3 Types of Natural Selection)

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3 Types of Natural Selection

• Directional
• Disruptive
• Stabilizing

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Kinds of Natural Selection acting on define
genetic variability in populations.
START WITH

• Directional Selection
• Define
• Reebop tails

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Kinds of Natural Selection acting on define
genetic variability in populations.
START WITH

• Disruptive Selection
• Define
• Tell the guppy
• story

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John Endlers Guppies

• Guppy populations in Trinidad.
• He found that
• male guppy colors range from brightly colored to
  drably colored
• Male guppies in streams with few predators are
  brightly colored, but in streams with many
  predators, they are drably colored like gravel.
• females prefer brightly colored males.

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Kinds of Natural Selection acting on define
genetic variability in populations.
START WITH

• Disruptive Selection
• Define
• Tell the guppy
• story

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Kinds of Natural Selection acting on define
genetic variability in populations.
START WITH

• Stabilizing Selection
• Define
• Human birth
• weight

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Human Babies and Birth Weight
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Kinds of Natural Selection acting on define
genetic variability in populations.
START WITH

• Stabilizing Selection
• Define
• Human birth
• weight

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Are There Other Ways to Alter Gene Frequency in a
Population?

• (In Addition to Natural Selection)

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Other Ways to Alter Gene Frequency in a Population

• Mutation
• Genetic drift
• Non-random mating
• Migration (genetic acquisition and loss)

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Other Ways to Alter Gene Frequency in a
Population

• Mutation
• Positive/negative/neutral mutations

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What causes gene variability in populations of
higher organisms?

• Higher organisms
• Mutation
• Positive/negative/neutral mutations
• Point mutations
• Substitutions/Insertions/Deletions

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Other Ways to Alter Gene Frequency in a Population

• Higher organisms
• Mutation
• Positive/negative/neutral mutations
• Point mutations
• Substitutions/Insertions/Deletions
• Gene transposition
• Individual genes
• Chromosomal rearrangement

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Other Ways to Alter Gene Frequency in a
Population

• Mutation
• Genetic drift
• Bottleneck

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Bottleneck Effect
Example North American Seal population
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A Story About Reebops and the Bottleneck Effect

• Reebops have only one predator, the Ruffledog.
  These animals are especially fond of
  straight-tailed Reebops because they are soooo
  tender. Each year 50 of the straight-tailed
  Reebops are lost to Ruffledogs
• Remember Straight tailhomozygous tt

RUFFLEDOG
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PROBLEMS

• REEBOPS 1998
• Population 200
• 50 straight-tailed Reebops
• Lose 50 straight-tailed Reebops to Ruffledog
• ? animals lost ? remain

• REEBOPS 2004
• Famine in the new millenium
• Population 12
• 3 straight-tailed Reebops
• Lose 50 straight-tailed Reebops to Ruffledog
• ? lost ? remains

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Review Bottleneck Effect
Which color might represent the straight-tailed
Reeboks????
How does this cause genetic drift?
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Other Ways to Alter Gene Frequency in a
Population

• Higher organisms
• Mutation
• Genetic drift
• Bottleneck effect
• Founder effect

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Founder Effect

• Associated with
• Small number sets up community in a new region
• Isolated population
• Inbreeding in population
• Example
• Ellis van Creveld syndrome in Amish community

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Other Ways to Alter Gene Frequency in a
Population

• Higher organisms
• Mutation
• Genetic drift
• Non-random mating

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Other Ways to Alter Gene Frequency in a Population

• Higher organisms
• Mutation
• Genetic drift
• Non-random mating
• Migration (allele acquisition and loss)

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Think/Write/Pair/Share

• Pick one mechanism of gene variability and write
  a story about the Reebops

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When is it Called Evolution?How do we know if
these events cause evolution?

• (Hint Hardy Weinberg Equilibrium Equation)

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Hardy-Weinberg Law

• Godfrey Hardy, Wilheim Weinberg
• This law describes a population that is NOT
  evolving or IN EQUILIBRIUM
• The Law
• p2 2pq q2 1
• (looks ugly
  but not impossible)

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Conditions of Hardy-Weinberg Law

• No mutation
• No natural selection
• Infinitely large population (no problem with
  Founders effect or genetic drift)
• Random mating
• No immigration or emigration
• If these are met the gene pool/allele frequency
  is in equilibrium and NO evolution is in process.
  
• WHAT DO THE ABOVE FACTORS DO FOR THE GENE
  POOL/ALLELE FREQUENCY? (WRITE/PAIR/SHARE)

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Can we use this to look at a populations allele
frequency and see if the population is evolving
or in equilibrium? Yes
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Using Hardy-Weinberg

• Albinism is a rare homozygous recessive (aa)
  trait.
• The most characteristic symptom is a deficiency
  in the skin and hair pigment melanin.
• Albinism occurs among humans as well as among
  other animals.
• The average human frequency of albinism in North
  America is about 1 in 20,000.

albino gorilla Snowflake
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Using Hardy-Weinberg

• Hardy-Weinberg equation
• p2 2pq q2 1
• q2 frequency of homozygous recessive
  individuals (aa)
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• 1 in 20,000 people with albinism are aa
• q2 1/20,000 0.00005
• q .007

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Using Hardy-Weinberg

• Knowing (q), it is easy to solve for (p)
• p 1 - q p 1 - .007 p .993
• So, the frequency of the dominant allele(A) is
  .99293 or about 99 in 100.

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Using Hardy-Weinberg

• Plug the frequencies of p and q into the
  Hardy-Weinberg equation
• p2 2pq q2 1
• (.993)2 2(.993)(.007) (.007)2 1
• .986 .014 .00005 1
• p2 predicted frequency of AA  .986 98.6
• 2pq predicted frequency of Aa  .014 1.4
• q2 predicted frequency of aa  .00005 .005

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Using Hardy-Weinberg

• With a frequency of .005 (about 1 in 20,000),
  persons with albinism are rare. 
• Heterozygous carriers for this trait, with a
  predicted frequency of 1.4 (about 1in 72), are
  far more common. 
• The majority of humans (98.6)probably are
  homozygous dominantand do not have the albinism
  allele.

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Lets calculate the Hardy-Weinberg equilibrium
using our Reebop allele frequencies.

• Question Are the Reebops that moved to a short
  grass/vegetation environment evolving?

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Use our Punnett Square to tell us about gene
frequencies after 5 generations
Pair with a partner to set up the H-W
equation p2 2pq q2 1 Plug in the numbers
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Use our Punnett Square to tell us about gene
frequencies after 5 generations
TT (.73 x .73) .53 p2 Tt 2(.73 x .27)
.4 2(p x q) Tt (.27 x .27) .07 q2
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Hardy-Weinberg Law

• CHECK THIS AGAIN
• The Law
• p2 2pq q2 1
• (looks ugly
  but not impossible)
• p2 2pq q2 1 .533 .394 .073 1???
• NO!
  .996
• TT (.73 x .73) .53 p2
• Tt 2(.730 x .27) .394 2(p x q)
• tt (.27 x .27) .073 q2

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Gene Frequency is not in Hardy Weiberg
Equilibrium.Therefore Reebops are evolving
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Macroevolution A New Species

• (Wow! This is really EVOLUTION.)

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Speciation the appearance of a new species

• When do you really have a new species?
• When 2 populations
• Exhibit different allele frequencies
• Are reproductively isolated
• Geographic, temporal, behavioral, mechanical,
  chemical isolation
• Infertile or not viable offspring

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Partner-Think/ Write/ Share with Table

• Remember the story about the Reebops that moved
  to the short grass/vegetation habitat. Expand
  this story so that the Reebops in the short grass
  habitat form a new species. Be sure to point out
  how they meet the criteria for a new species.
• (If you want you can write an entirely new story)

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Go Back and Think About it Questions

• Think, Write/Pair/Share

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NOW LETS CONSIDER SOME STATEMENTS ABOUT NATURAL
SELECTION

• T/F Natural selection acts only by removing the
  mistakes
• T/F Natural selection saves the successes and
  deletes the mistakes
• T/F The only good mutation is no mutation. All
  mutations are bad.
• T/F Natural selection always produces a
  fitter or eugenic gene pool.

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THE END