Measuring evolution
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MEASURING EVOLUTION. When is it Called Evolution?. Microevolution : Changing Allele Frequencies in Populations. Macroevolution : Speciation. Let’s ask an important question:. Can Reebops evolve?. Why do you think they could or could not?

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MEASURING EVOLUTION

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MEASURING EVOLUTION


When is it Called Evolution?

Microevolution: Changing Allele Frequencies in Populations

Macroevolution: Speciation


Let’s ask an important question:


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


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.


ASICS MOUNTAINS

AVIA DESERT

PLANTAR GORGE

NEW BALANCE RIVER

BROOKS MEADOW

TENDONITIS MEADOW

KEDS LAKE

ADIDAS SWAMP

REEBOP COUNTRY

NIKE WOODS


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

  • Set up a scientific inquiry.

  • Gather data

  • Interpret data


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


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”


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?


T

t

TT

Tt

T

t

Tt

tt

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?


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?


Now it’s your turn: Do the Natural Selection Experiment with Reebops

(a 5 generation experiment)


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?


Sample DataDid Our Reebop Population Evolve?


T(.5)

T(.73)

t(.5)

t(.27)

TT

TT

Tt

Tt

T(.73)

T(.5)

t(.5)

t(.27

tt

tt

Tt

Tt

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) = .


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


Natural Selection Doesn’t Always “Select” the Same Way

(3 Types of Natural Selection)


3 Types of Natural Selection

  • Directional

  • Disruptive

  • Stabilizing


Directional Selection

Define

Reebop tails

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

# organisms

# organisms

# organisms

trait

1

1

5

5

7

7

9

9

11

11

Straight Curly

START WITH:


Disruptive Selection

Define

Tell the guppy

story

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

# organisms

# organisms

trait

1

5

7

9

11

START WITH:


John Endler’s 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.


Disruptive Selection

Define

Tell the guppy

story

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

# organisms

# organisms

# organisms

trait

1

1

5

5

7

7

9

9

11

11

bright drab

START WITH:


Stabilizing Selection

Define

Human birth

weight

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

# organisms

# organisms

trait

1

5

7

9

11

START WITH:


Human Babies and Birth Weight


Stabilizing Selection

Define

Human birth

weight

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

# organisms

# organisms

# organisms

trait

1

1

5

5

7

7

9

9

11

11

Birth Weight

START WITH:


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

(In Addition to Natural Selection)


Mutation

Genetic drift

Non-random mating

Migration (genetic acquisition and loss)

Other Ways to Alter Gene Frequency in a Population


Mutation

Positive/negative/neutral mutations

Other Ways to Alter Gene Frequency in a Population


Higher organisms

Mutation

Positive/negative/neutral mutations

Point mutations

Substitutions/Insertions/Deletions

NORMAL

SUBSTITUTION

INSERTION

DELETION

What causes gene variability in populations of higher organisms?


Higher organisms

Mutation

Positive/negative/neutral mutations

Point mutations

Substitutions/Insertions/Deletions

Gene transposition

Individual genes

Chromosomal rearrangement

Other Ways to Alter Gene Frequency in a Population


Mutation

Genetic drift

Bottleneck

Other Ways to Alter Gene Frequency in a Population


Bottleneck Effect

Example: North American Seal population


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 tail=homozygous; tt

RUFFLEDOG


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

1.5

1.5

25

25

PROBLEMS


Review Bottleneck Effect

Which color might represent the straight-tailed Reeboks????

How does this cause genetic drift?


Higher organisms

Mutation

Genetic drift

Bottleneck effect

Founder effect

Other Ways to Alter Gene Frequency in a Population


Associated with:

Small number sets up community in a new region

Isolated population

Inbreeding in population

Example:

Ellis van Creveld syndrome in Amish community

Founder Effect


Higher organisms

Mutation

Genetic drift

Non-random mating

Other Ways to Alter Gene Frequency in a Population


Higher organisms

Mutation

Genetic drift

Non-random mating

Migration (allele acquisition and loss)

Other Ways to Alter Gene Frequency in a Population


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

ASICS MOUNTAINS

AVIA DESERT

PLANTAR GORGE

NEW BALANCE RIVER

BROOKS MEADOW

TENDONITIS MEADOW

KEDS LAKE

ADIDAS SWAMP

REEBOP COUNTRY

NIKE WOODS

Think/Write/Pair/Share


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

(Hint: Hardy Weinberg Equilibrium Equation)


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)


Conditions of Hardy-Weinberg Law

  • No mutation

  • No natural selection

  • Infinitely large population (no problem with Founder’s 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)


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


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”


Using Hardy-Weinberg

Hardy-Weinberg equation:

p2 + 2pq + q2 = 1

q2 = frequency of homozygous recessive individuals (aa)

  • 1 in 20,000 people with albinism are aa

    q2 = 1/20,000 = 0.00005

    q = .007


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.


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%


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.


Let’s calculate the Hardy-Weinberg equilibrium using our Reebop allele frequencies.

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


T(.73)

t(.27)

TT

Tt

T(.73)

t(.27

tt

Tt

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


T(.73)

t(.27)

TT

Tt

T(.73)

t(.27

tt

Tt

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


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


Gene Frequency is not in Hardy Weiberg Equilibrium.Therefore Reebops are evolving


Macroevolution – A New Species

(Wow! This is really EVOLUTION.)


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


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)


Go Back and Think About it Questions

Think, Write/Pair/Share


NOW LET’S 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.


THE END


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