mechanisms of evolution 15.3. preview changes in allele frequencies causes evolution changes in...

Mechanisms of EvolutionMechanisms of Evolution

15.315.3

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Changes in allele Changes in allele frequencies causes frequencies causes evolutionevolution

3 Types of natural selection3 Types of natural selectionHow new species formHow new species formSpeed of EvolutionSpeed of EvolutionPatterns of evolutionPatterns of evolution

I. Allele FrequenciesI. Allele Frequencies

A. Review: What is an allele?A. Review: What is an allele?OneOne form of a gene that causes form of a gene that causes different traits to appear different traits to appear

(Ex: pink, red, or white (Ex: pink, red, or white petals)petals)

B. B. Allelic FrequencyAllelic Frequency- The % of a - The % of a specific allele in the gene pool.specific allele in the gene pool.

C. C. Gene PoolGene Pool- ALL possible - ALL possible alleles in a populationalleles in a population

I. Allele FrequenciesI. Allele Frequencies

D. D. Genetic EquilibriumGenetic Equilibrium- A - A population in which the population in which the allelic frequency stays the allelic frequency stays the samesame

1. 1. Evolution is NOT Evolution is NOT occurring!!!occurring!!!

II. Genetic DriftII. Genetic Drift

A. A. Genetic DriftGenetic Drift- An evolution - An evolution mechanism in which the mechanism in which the allelic frequencies are allelic frequencies are changed due to chance.changed due to chance.

1. Mutations occur by 1. Mutations occur by chance, not caused by UV chance, not caused by UV rays, chemicals, radiation, rays, chemicals, radiation, etc.etc.


2. Greatly affects SMALL 2. Greatly affects SMALL populations.populations.

a. Ex: Amish populationsa. Ex: Amish populations1) 30% of settlers carried a 1) 30% of settlers carried a

recessive allele for extra fingers & recessive allele for extra fingers & toes.toes.

2) Today 1/14 Amish carry 2) Today 1/14 Amish carry the allele compared to 1/1000 non-the allele compared to 1/1000 non-Amish United States CitizensAmish United States Citizens

III. Natural SelectionIII. Natural Selection

A. Allele frequencies change A. Allele frequencies change because organisms with because organisms with traits that fit their traits that fit their environment survive and environment survive and reproduce (others die).reproduce (others die).

B. Affects small AND large B. Affects small AND large populationspopulations


C. Types of Natural Selection C. Types of Natural Selection (WHO (WHO DOES IT FAVOR???)DOES IT FAVOR???)1. 1. Stabilizing SelectionStabilizing Selection- Favors - Favors average individuals average individuals

a. Big spiders are seen by birdsa. Big spiders are seen by birdsb. Small spiders can’t find foodb. Small spiders can’t find foodc. Medium spiders are favoredc. Medium spiders are favored

(see graph on pg. 408)(see graph on pg. 408)

III. Natural SelectionIII. Natural Selection2. 2. Directional selectionDirectional selection- Favors - Favors ONEONE extreme for a trait. extreme for a trait.

a. Insects are found deep in a. Insects are found deep in a tree trunk.a tree trunk.b. Woodpeckers with short b. Woodpeckers with short

& & medium length beaks medium length beaks have have trouble getting to the trouble getting to the insects.insects. c. Long beaks are c. Long beaks are favored.favored.


3. 3. Disruptive SelectionDisruptive Selection- Favors - Favors BOTHBOTH extremes, but not extremes, but not intermediate phenotypes.intermediate phenotypes. a. A beach has white and dark a. A beach has white and dark brown rocksbrown rocks

b. White and dark brown b. White and dark brown snails cannot be seen by birdssnails cannot be seen by birds

c. Tan snails can be seen on c. Tan snails can be seen on either color of rock and are eateneither color of rock and are eaten

Remember the green car?

IV. SpeciationIV. Speciation

A. A. SpeciesSpecies- Group of - Group of organisms that look alike, organisms that look alike, interbreed and produce interbreed and produce fertile fertile offspring.offspring.

B. B. SpeciationSpeciation- The evolution - The evolution of new species.of new species.


C. Causes of speciationC. Causes of speciation

1. 1. Geographic IsolationGeographic Isolation- - When a physical barrier When a physical barrier divides a population and the divides a population and the two pops evolve differently. two pops evolve differently.

a. Different alleles appear a. Different alleles appear in in the two populations the two populations


2. 2. Reproductive IsolationReproductive Isolation- - When closely related When closely related organisms can no longer organisms can no longer produce fertile offspring.produce fertile offspring.

a. Genetic material a. Genetic material becomes becomes too differenttoo different

b. Reproductive behaviors b. Reproductive behaviors become too differentbecome too different


Rana boylii Breeds late

March to May

Rana auroraBreeds

January to March


3. Change in Chromosome #3. Change in Chromosome #

a. a. PolyploidPolyploid- Individual or - Individual or species with more than the species with more than the normal set of chromosome normal set of chromosome

(3n, 4n, 5n etc)(3n, 4n, 5n etc)

b. Caused by mistakes in b. Caused by mistakes in meiosismeiosis


c. Organisms with different c. Organisms with different # # of chromosomes cannot of chromosomes cannot produce fertile offspringproduce fertile offspring

d. Polyploids CAN d. Polyploids CAN interbreed interbreed among among themselves if they themselves if they have have the same # of the same # of chromosomeschromosomes


D. Speciation RatesD. Speciation Rates1. 1. GradualismGradualism- Evolution - Evolution occurs at slow, steady rateoccurs at slow, steady rate2. 2. Punctuated EquilibriumPunctuated Equilibrium- - Evolution occurs in short Evolution occurs in short bursts with long periods of bursts with long periods of equilibrium in between.equilibrium in between.

(See Elephants on pg. 411)(See Elephants on pg. 411)


3. Both gradualism and 3. Both gradualism and punctuated equilibrium are punctuated equilibrium are accepted today.accepted today.

4. Side Note: Phylogenic 4. Side Note: Phylogenic TreeTree

V. Patterns of EvolutionV. Patterns of Evolution

A. A. Adaptive RadiationAdaptive Radiation- One - One species evolves into an array species evolves into an array species to fit different niches species to fit different niches (mini habitats)(mini habitats)1. Diversity allows for more 1. Diversity allows for more flexibility and larger numbersflexibility and larger numbers

2. Supports the idea of 2. Supports the idea of natural selectionnatural selection


B. B. Divergent EvolutionDivergent Evolution- Similar - Similar species become increasingly species become increasingly different.different.

C. C. Convergent EvolutionConvergent Evolution- Very - Very distantly related organisms distantly related organisms become more similarbecome more similar1. They share similar 1. They share similar environments and selection environments and selection pressures pressures

RecapRecap

A. Changes in allele A. Changes in allele frequencies causes frequencies causes evolutionevolution

B. 3 Types of natural B. 3 Types of natural selectionselection

1. Stabilizing 1. Stabilizing

2. Directional 2. Directional

3. Disruptive3. Disruptive

RecapRecap

C. Speed of evolutionC. Speed of evolution

1. Gradualism1. Gradualism

2. Punctuate equilibrium2. Punctuate equilibrium

RecapRecapD. How new species formD. How new species form

1. Geographic Isolation1. Geographic Isolation

2. Reproductive Isolation2. Reproductive Isolation

3. Changes is chromosome #3. Changes is chromosome #

E. Patterns of evolutionE. Patterns of evolution1. Adaptive Radiation1. Adaptive Radiation

2. Divergent Evolution2. Divergent Evolution

3. Convergent Evolution3. Convergent Evolution

mechanisms of evolution 15.3. preview changes in allele frequencies causes evolution changes in...

Documents

speciation slide

different slide

meiosis slide

genetic drift slide

allele frequencies

evolution changes

evolution of new species

causes of speciation