EvolutionLearning Targets 1-17

Guided Reading Review

Charles DarwinHMS Beagle

• Born in England in 1809• A Naturalist (studied nature)• Took a 5yr voyage on a ship called

the HMS Beagle to study the organisms encountered on the journey

• Traveled to the Galapagos Islands near S. America

• Here he made many observations about the organisms he saw there; including tortoises and finches

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Darwin’s Observations• Each island of the

Galapagos have a different climate.

• Found that tortoises had different shells depending on the island they inhabited

• Found that finches had different beaks

• He also found fossils similar to living organisms and some like he had never seen before

The Ride HomeAfter leaving the Galapagos Islands, Darwin had a

few questions.

• Why do organisms have differences based on their habitat?

• Why had so many species disappeared?• How are they related to those still living?• Were similar organisms formerly the same

species?

Guided Reading Review

Other Old Dead DudesDarwin, being a good scientist, studied the works of

other scientists in and outside of his field.

Darwin

Malthus

Lamarck

HMS Beagle

HuttonLyell

Geologists

Economist

Naturalist

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What Darwin ConcludedCharles Darwin

From Hutton and Lyell:1. If the Earth can change, can life also

change?2. Geological processes take a long time,

therefore the Earth must be old.

From Malthus:3. That organisms will have more

offspring than will die and this will lead to competition.

4. Not all offspring live so what makes some survive and others

die?

What everyone else thought

1. The Earth was made as it was now and did not change

2. The Earth is only a few thousand years old

3. Organisms don’t change

**Darwin’s conclusions caused a BIG buzz**

Guided Reading Review

That Other GuyJean Baptiste Lamarck

• All living things change over time• Living things descend from other

living things• Organisms adapt to their

environment• Selective USE or DISUSE of

organs will cause organisms to gain or lose the trait during their lifetime

• Traits lost or gained will be passed onto the organism’s offspring.

• Loss or acquisition of a trait is to move toward being perfect and better suited for their environments

Lamarck

Guided Reading Review

Darwin’s Idea• Knowing that his ideas were not going to be well

received, Darwin wrote a book called On the Origin of Species, but did not publish it for a long time.

• His idea was…o Natural Selection (nature “selects” organisms to survive based on

the most favorable trait for the environment)o Every species has variations within a trait and the variations are

IMPORTANTo Some of the traits were inheritableo Those organisms that have favorable traits (ADAPTATIONS) will

survive and go on to have more offspring (FITNESS) o SURVIVAL OF THE FITTESTo Over many generations, an adaptation could spread throughout the entire species.

o In this way, according to Darwin, evolution by natural selection would occur.

Noodle WormsPost “Noodle Worm Lab” we can say…1. Variations do exist within the population

(green, orange, white worms)-Where did it come from? Why Genetics, silly!

2. Some worms did struggled to survive.3. Those that did live were best suited or “most fit” and

possess a color characteristic that makes them more likely to survive.

4. Those that survived can pass their characteristic to the next generations (a.k.a descending with modifications)

Variations So do variations exist in all populations? How do they go from parent to offspring?

1. Meiosis• Cells copy DNA• Crossing over events take place in Prophase I

2. Fertilization from SEXUAL reproduction• Egg + Sperm• Individual sets of chromosomes combine to form

offspring with features unique from either parent

Variations 3. Mutations• By Chance, radiation, and chemicals• Give new genetic material to the gene pool

4. Genetic Drift

5. Migration/Gene Flow

All of these forces change GENOTYPES, PHENOTYPES, and determine the amount of GENETIC VARIATION

VariationsGene pool – all members of an

interbreeding population who bring genetic variety to the population.

• So all the BB, Bb, or bb in the buffalo herd

Relative frequency – percentage of time a particular allele appears in the gene pool compared to other alleles

• What is the % of B’s to the % of b’s in the buffalo herd

Putting It All TogetherEvolution

(Darwin)1859

Genetics(Mendel)

Mid 1800’s

DNA(Watson & Crick)

1963

Current Understanding of

Biological Evolution

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Putting It All TogetherOkay, then…so, Based on the Mouse WS and the Moths Activity,

Evolution – a change in the relative frequency of alleles in a population over time

Evolutionary fitness – the success with which an individual can pass their traits to the next generation

Therefore, POPULATIONS, NOT INDIVIDUALS, evolve

Putting It All Together• Evolution NEVER acts

DIRECTLY on ONE GENE.• Evolution works on the

entire organism

• If the organism has evolutionary fitness and– Reproduces = gene(s) in

the gene pool– Does not reproduce =

NO gene(s) in the gene pool

NS on a Single Gene TraitSingle gene trait – one gene controls a trait.• Only two phenotypes (Widow’s peak or no

widow’s peak)• Three genotypes (WW, Ww or ww)• Two alleles (W and w) in this example

• Natural selection can work on each phenotype and change the allelic frequency

NS on a Polygenic TraitPolygenic Trait- when a trait is controlled by more than one

gene• A range of phenotypes (a bell curve)• Many genotypes• At least two alleles per gene• Natural selection effect is more complex

fitness of individual close on curve is similar fitness of individuals further apart is varied. This is where

NS can act.

NS on a Polygenic TraitThree Effects on Phenotypes1. Directional Selection - when one end of the

curve has higher fitness than the middle or other end of the curve

*Shifts the curve left or right*

Peccaries eat cacti. Cacti with fewer spines are eaten

first. Thus, the cacti with more spines fair better . NS

moves the curve toward cacti that

make many spines

NS on a Polygenic Trait2. Stabilizing Selection – when individuals in the

middle of the curve have higher fitness than those on the ends.

*Narrows the graph*

Peccaries continue to eat the cacti with few spines (left of graph). A parasitic

insect lays its eggs at the cacti spine base and therefore loves

cacti with lots of spines (right of graph). Both

extremes are NOT fit. Being in the middle is best

NS on a Polygenic Trait3. Disruptive Selection – when individuals at the

upper and lower ends of the curve have higher fitness

*Creates 2 peaks in graph/phenotype*

A road through the desert brings tourists that love

to pick cacti as souvenirs. Too

few spines on the cacti look bad and too many

spines are hard to pick. Thus,

cacti with spine numbers in the

middle are picked.

Other Factors of Evolutionary Change

Variation(crossing over, meiosis,

sexual reproduction, and mutations)

4. Genetic Drift 5. Migration

Natural Selection

Evolutionary Change

Note…NS does not create variation, it just works on it

Genetic DriftGenetic drift – is evolution BY CHANCE!; changes in a population that result from random chance or “luck”

• Luck ≠ evolutionary fitness• Luck ≠ “better”• Affects all populations• Natural selection produces adaptations, Genetic Drift does

not

Genes of one generation do not wind up in identical ratios in the next generation, but…it’s still evolution!

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Genetic Drift• By random chance,

the brown frogs die• Their genes are thus

unable to be passed to the next generation

• Thus the gray and greens are the only ones able to mate and pass on genes.

• Variation is thereby decreased

Genetic DriftEffects of Genetic Drift:1. A decrease in variation within a

population/change in the relative frequency– May decrease a populations ability to respond to

selection pressures

2. Acts FASTER and is more DRAMATIC in small populations– Very bad for rare or endangered species

3. Can cause new species to emerge

Genetic DriftPopulation bottleneck – a decrease in population size for at least one generation

– Causes a decrease in variation– Worse for small populations (even

if for a short time)– Makes responding to selective

pressures harder

Causes:1. Overhunting2. Environmental Disaster

(hurricane, flood, etc)3. Habitat Destruction

Genetic DriftFounder Effect – when a portion of an original population breaks off and form a new population. • Also decreases

variability because the small group may not be equally representative of the larger population’s variability

Hardy-Weinburg

Recall that evolution -is the change in the relative frequency of alleles in a population over time.

VersusGenetic equilibrium - No evolution – no changes

in the relative frequencyWhen does this happen? Under what

conditions?

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Hardy-WeinburgA: The relative frequency of alleles in a population will

remain constant UNLESS 1 or more factors cause the frequency to change.

Five Conditions for GE:1. Random Mating – equal opportunity for all member to produce young. – This is rarely random!

2. The population is large – this decrease the effects of genetic drift

Hardy-Weinburg3. No immigration or emigration – Immigration = new individuals move in and bring

new alleles and variety– Emigration = individuals leave the population

and take allelic variety with them

4. No mutations5. No natural selection– All genotypes have equal probability for survival

Hardy-Weinburg• For some populations these conditions

are met, or nearly met, for long periods of time.– Conditions met = genetic equilibrium– Conditions not met = evolution

– There are two equations that can be used to show changes.

• p2 + 2pq + q2 = 1 • p + q = 1•Where p = dom.

allele freq and q = rec.

allele freq

Geologic Time & Evidence for Evolution

Please see the Guided Reading Posted to the website for the answers and “notes” for

Geologic Time and Evidence for Evolution(LT 9-13)

LT 9-13

CladogramsCladogram – a diagram that shows evolutionary relationships

among groups

• Based on phylogeny (the study of evolutionary relationships)• Sometimes called a phylogenic tree (although the two vary

slightly)• Cladistics - the practice of looking at “innovations,” or

newer features, that serve some kind of purpose

• Derived characteristics – new features that appear in later generations but not earlier ones

Let’s see one made

LT 9-13

Cladogram

1. ______ Wings2. ______ 6 Legs3. ______ Segmented Body4. ______ Double set of wings5. ______ Jumping Legs6. ______ Crushing mouthparts7. ______ Legs8. ______ Curly Antennae

CladogramsTo make a cladogram, you must first look at the animals you are

studying and establish characteristics that they share and ones that are unique to each group. For the animals on the table, indicate whether the characteristic is present or not. Based on that chart, create a cladogram like the one pictured above.

Cells Backbone Legs Hair Opposable Thumbs

Tiger

Slug

Frog

Catfish

Human

SpeciationLT 14

Extinction• 99% of all life that has ever existed is now extinct• mass extinctions have occurred many times in

the Earth’s history

• Extinctions indicate…– Organisms who were selected against by nature– A failure to adapt – A collapse in an organism’s environment they could

not help

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ExtinctionWhat becomes of those organisms that live

(evolutionarily speaking, of course)? • When large groups of organisms die, it leaves

habitats and niches open for others to move into.• New habitats can also have new selective pressures

that will work on organisms. – This could cause evolution within a species OR– Adaptive radiation – a species has evolved from a

common ancestor into diverse forms that live in different ways

Types of EvolutionA. Divergent Evolution-when

selective pressures cause two species to form (think speciation)

B. Convergent Evolution-takes place when species of different ancestry begin to share similar traits because of a shared environment or other selection pressure.

C. Co-evolution- organism of different species but have a close relationship and evolve together

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Rates of EvolutionDarwinbelieved evolution was a SLOW process; Gradualism

Modern Biologistthink that some evolution is slow and other times long periods of equilibrium are followed by RAPID evolution-Punctuated Equilibrium

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