WARM-UP

• On your warm-up paper– What conditions caused the average shade of

the “dot” population to evolve?

• Your lab (dot lab)– OPEN YOUR LAB BOOKS AND HAVE YOUR

GRAPHS ON YOUR TABLE

Evolution:

Change in the heritable (genetic) traits of a population over time

Note: when we discuss evolution, we are talking aboutpopulations changing, not individuals

Natural selection:

The main mechanism by which evolution occurs

4 Conditions for Natural Selection:

1. Variation: Individuals in a population are not identical to each other.

2. Inheritance: Traits are passed to offspring; traits have a genetic basis

3. Environmental population limits: Environmental limiting factors prevent all individuals from surviving to reproduce; some die young.

4. Environmental selection: • Individuals in the population with more

favorable (advantageous) traits are the ones that survive to reproduce.

• Individuals without advantageous traits die before reproducing.

These factors result in a change in the average trait of the population… Biologists call this EVOLUTION!

1. VARIATION

• Members of a population have traits similar to the average trait of the entire population, but they are not identical.

Fre

quen

cy

Height (cm)

Mean (average) heightYOUR TURN: Using height as an example, sketch a graph to represent the statement above.

2. INHERITANCE

• DNA determines the traits of individuals

• Individuals inherit DNA from their parents

• This causes the traits of the offspring to resemble the traits of the parents

DNA mRNA protein trait

3. ENVIRONMENTAL POPULATION LIMITS

A. For all species, if every individual born into a population were to reproduce, the population would grow exponentially

Time

Pop

ulat

ion

B. Environmental factors (limiting factors) prevent the majority of individuals from surviving to reproduce

3. ENVIRONMENTAL POPULATION LIMITS

Pop

ulat

ion

Time

4. SELECTION

• Individuals without advantageous traits die before reproducing.

• Individuals with advantageous traits survive to reproduce.

These

indi

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die

withou

t rep

rodu

cing

These individualssurvive to reproduceF

requ

ency

Characteristic

Populations change, not individuals

• The “average” characteristic or other measure of the population changes over generations

Fre

quen

cy

Characteristic

aver

age,

1st g

en.

These

indi

vidua

ls

die

withou

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cing

aver

age,

2nd

gen

.

These

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die

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rodu

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aver

age,

3rd

gen

.

aver

age,

50th g

en.

These individualssurvive to reproduce

The environment is the selective force behind evolution

• The environment determines what characteristics are “favorable”

• Because the environment changes over time, the characteristic that is more favorable for a population changes

• Therefore, characteristics of the population change, or evolution occurs

Questions for discussion

WARM-UP

Take out your notes sheet from last class

Take out your Peppered Moth Homework

On your warm-up paper:

1. What role do you think mutation plays in evolution?

2. Where does mutation fit in with the 4 factors for Natural Selection?

Evolution of Peppered Moths

Before we learn about how mutation influences evolution, let’s discuss the evolution of peppered moths we read about last night…

Dark form

Peppered form

Explain the evolution of color in the peppered moth population.

1. Describe what trait evolved.

2. Describe how each of the 4 conditions for natural selection exists in the moth example:

1. Variation

2. Inheritance

3. Population limits

4. Selection

• The population of peppered moths became darker in color near industrial areas.

• Originally, some moths were dark, some moths were peppered (light).

• Color is determined by genes inherited from parents.

• Not all moths survive to reproduce- some are eaten by birds.

• Pollution killed lichen and made the environment darker, so darker moths were better camouflaged and not eaten as much as peppered (light) moths.

• This caused the average color of the moth population to become darker

Explanation revised... Controversy!

Remember that evolution means change in a population’s traits. Scientists agree that evidence shows evolution of the moths has occurred.

Natural selection is the mechanism for the change, and recent evidence suggests that camouflage might not be the sole reason for the environmental selection.

?- Sunlight absorption and heat

What you will learn today…

1. How do we measure genetic variation in a population?

2. Why is genetic variation in a population important?

3. What are the sources of genetic variation in a population?

What determines a heritable trait?

DNA(gene) mRNA protein Observed

trait

transc

riptio

n

transla

tion

protein fu

nction

(enzy

me activit

y)

Therefore, if traits vary in a population, then the genes (alleles) must vary in the population!

A population with variation in traits…

Grey

White

Tall ears

Short ears

...is caused by variation in alleles

Grey allele = G

White allele = g

Tall ear allele = T

Short ear allele = t

T tG G

t tg g

T TG g

t tG g

t tG g

t tG g

t tG G

T tg g

How do we measure genetic variation in a population?

Grey allele = G

White allele = g

Tall ear allele = T

Short ear allele = t

T tG G

t tg g

T TG g

t tG g

t tG g

t tG g

t tG G

T tg g

“Gene Pool”

8 / 16 = 50% G

8 / 16 = 50% g

4 / 16 = 25% T

12 / 16 = 75% t

How do we measure genetic variation in a population?

Gene Pool- Total genetic information available in a population (all the alleles that are present).

Allele Frequency- The percentage of an allele in the gene pool. Tells you whether a given allele is common or rare.

Why is genetic variation in a population important?

• A gene pool without much variation limits a species’ ability to further evolve. (Variation is one of the 4 factors required for natural selection to cause evolution)

• If populations do not adapt to their environment, they may become extinct.

Sources of genetic variation

1) SEXUAL REPRODUCTION

A. Meiosis – one allele is passed on from each parent (recall that sperm and eggs are haploid cells, each containing half the necessary genetic information).

B. Random fertilization – only one of the millions of sperm involved in mating will fertilize the egg.

The randomness of sexual reproduction

explains why siblings can look so different.

Sources of genetic variation

2) MUTATIONMutation means a change in DNA sequence.A new DNA sequence = new allele of a gene.

– Many mutations produce genes that are harmful (e.g. Huntington’s disease)

– Some mutations produce genes that are neutral (neither helpful nor harmful)

– Very, very few mutations produce genes that are advantageous

• Mutations add new alleles to the gene pool. That is, they increase the variety of alleles in the population.

Deck of Cards AnalogyDeck is Gene Pool – It contains all possible

alleles for the next generation.Drawing cards picks the alleles that are

inherited by the next generation.

Shuffling of the deck is sexual reproduction.Adding new cards to the deck is mutation.

(Mutation is rare, but shuffling happens each time a new generation is produced)

Natural Selection

• Individuals with advantageous genes survive to reproduce and pass on these genes to their offspring.

• Individuals without advantages genes do not survive to reproduce, and these genes do not get passed on in the population.

Conclusion

• Mutation does NOT cause evolution – it is only a source of variation (just one of the

factors required for natural selection)

• Natural selection determines if the allele frequency will change within a population.

• Change in allele frequency = EVOLUTION

Explain the change in allele frequency in the peppered moth population.

WARM-UP

– 1. Define “theory” in your own words.– 2. What is the difference between the way

scientists use the word “theory” and the way we use it in regular conversation?

– 3. How are theories made?

Directions

1. Make observations about the cube

2. Develop a hypothesis for the “rules” defining the relationships between the letters, numbers, and colors on the sides of the cube.

3. Make specific predictions for unknown sides based on your hypothesis.

4. When you are ready to test your hypothesis, compare your predictions with observations of the new sides provided by your teacher.

Obtain new data, observe, revise hypotheses, make new testable predictions

WARM-UP

– Did you answer the question at the end of the reading??

– Compare and Contrast hypothesis and theory.

Take out your Theory Cube Worksheet

Put your Kerosene Karl HW in a pile on your desk