EVOLUTION/POPULATION GENETICS CH. 15-16. SOME INFLUENCES ON DARWIN’S THOUGHT LAMARCK MALTHUS LYELL...

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EVOLUTION/POPULATION GENETICS

CH. 15-16

SOME INFLUENCES ON DARWIN’S THOUGHT

• LAMARCK• MALTHUS• LYELL• HUTTON• WALLACE

Contributor’s to Darwin’s thinking included:

• Charles Lyell –uniformatarianism

• Georges Cuvier – species extinction (Catastrophism)

• Thomas Malthus – struggle for existence (resources)

Contributor’s to Darwin’s thinking included:

• James Hutton - Gradualism• John Baptiste Lamarck –

Inheritance of acquired Characteristics and Law of Use and Disuse

• Alfred Russel Wallace – organisms evolved from common ancestors

Lamarck’s Theory of Evolution

• Jean-Baptiste Lamarck, 1809

• One Of First Scientists To Understand That Change Occurs Over Time

• Stated that Changes Are Adaptations To Environment acquired in an organism’s lifetime

• Said acquired changes were passed to offspring

• Idea called Law of Use and Disuse

• If a body part were used, it got stronger

• If body part NOT used, it deteriorated

• Inheritance Of Acquired Traits– Traits Acquired During Ones Lifetime

Would Be Passed To Offspring

Clipped ears of dogs could be passed to offspring!

Lamarck’s Mistakes

• Lamarck Did NOT Know how traits were inherited (Traits are passed through genes)

• Genes Are NOT Changed By Activities In Life

• Change Through Mutation Occurs Before An Organism Is Born

Population Growth

• Thomas Malthus, 1798

• Economist

• Observed Babies Being Born Faster Than People Were Dying

• Population size limited by resources such as the Food Supply

The Struggle for Existence

• Malthus’ Influence:– High Birth Rates & Limited Resources

Would Force Life & Death Competition

• Each Species Struggles For:– Food– Living Space– Mates

Population Growth

• Malthus Reasoned That If The Human Population Continued To Grow Unchecked, Sooner or Later There Would Be Insufficient Living Space & Food For Everyone

• Death Rate Will Increase To Balance Population size & Food Supply

Population Growth• Darwin Realized

Malthus’s Principles Were Visible In Nature

• Plants & Animals Produce Far More Offspring Than Can Be Supported– Most Die– If They Didn’t – Earth

Would Be Overrun

Charles Lyell• Proposed theory of

Uniformitarianism• Geological processes

at uniform rates building & wearing down Earth’s crust

• Proposed that the Earth was millions of years instead of a few thousand years old

Principles of Geology

• Published by Lyell Just Before The Beagle Set Sail & read by Darwin

• Explained Geological Processes That Shaped The Earth

• Helped Darwin Understand Sea Shells In The Andes Mountains At 12,000+ Feet

– Expanded Earth’s Age

Hutton’s Theory of Geological Change

•James Hutton, 1795, Scottish geologist•Studied invertebrate fossils in Paris Museum•Described The Geological Forces That Have Changed Life on Earth Over Millions of Years (erosion, earthquakes, volcanoes…)

Hutton’s Theory of Geological Change

• Changes in Earth’s crust due to slow continuous processes

• Idea Known as

Gradualism

Wallace’s Contribution

• Alfred Russel Wallace Independently came to same Conclusion as Darwin that species changed over time because of their struggle for existence

• When Darwin read Wallace’s essay, he knew he had to publish his findings

Darwin's Theory

1. Individual Organisms In Nature Differ From One Another. Some Of This Variation Is Inherited

2. Organisms In Nature Produce More Offspring Than Can Survive, And Many Of These Offspring Do No Reproduce

Darwin's Theory

3. Because More Organisms Are Produced Than Can Survive, Members Of Each Species Must Compete For Limited Resources

4. Because Each Organism Is Unique, Each Has Different Advantages & Disadvantages In The Struggle For Existence

Darwin's Theory

5. Individuals Best Suited To Their Environment Survive & Reproduce Successfully – Passing Their Traits To Their Offspring.

6. Species Change Over Time. Over Long Periods, Natural Selection Causes Changes That May Eventually Lead To New Species

Darwin's Theory

7. Species Alive Today Have Descended With Modifications From Species That Lived In The Past

8. All Organisms On Earth Are United Into A Single Tree Of Life By Common Descent

Concept MapSection 15-3

includes

Evidence of Evolution

Physical remains of organisms

Common ancestral species

Similar genes Similar genes

which is composed of which indicates which implies which implies

The fossil recordGeographic

distribution of living species

Homologous body structures

Similaritiesin early

development

Homologous StructuresHomologous Structures

Turtle Alligator Bird Mammal

Ancient lobe-finned fish

HOMOLOGOUS STRUCTURESSection 15-3

Homologous Body Structures

• Not All Serve Important Functions– Vestigial Organs

• Appendix In Man• Legs On Skinks

Evidence for Evolution - Comparative Embryology

Similarities In Embryonic Development

Fossil Record

• Earth is Billions of Years Old

• Fossils In Different Layers of Rock (sedimentary Rock Strata) Showed Evidence Of Gradual Change Over Time

Beaver

NORTH AMERICA

Muskrat

Capybara SOUTH AMERICA

Geographic Distribution of Living SpeciesSection 15-3

Beaver

Muskrat

Beaver andMuskrat

Capybara

Coypu andCapybara

Similarities in DNA Similarities in DNA SequenceSequence

Evolutionary Time Scales

Macroevolution: Long time Long time scale events scale events

that create and that create and destroy destroy species.species.

Microevolution:

Short time scale events

(generation-to-generation) that

change the genotypes and phenotypes of

populations

Evolutionary Time Scales

Sample Population

48% heterozygous

36% homozygous

16% homozygous

Frequency of Alleles

allele for brown fur

allele for black fur

VARIATION & GENE POOLS: GENE POOL, RELATIVE FREQUENCY OF GENES/ALLELESSection 16-1

Relative frequency # of times an allele occurs in a gene pool, compared w/ the # of times other alleles for the same gene occur

MUTATION

• THE ULTIMATE SOURCE OF GENETIC VARIATION!!!!!!

0 Widow’s peak No widow’s peak

Phenotype

Phenotypes for Single-Gene Trait: The # of phenotypes a given trait has is determined by how many genes

control the traitSection 16-1

Controlled by a single gene that has 2 alleles leads to 2 distinct phenotypes

Phenotype (height)

Generic Bell Curve for Polygenic Trait: many possible genotypes and phenotypesSection 16-1

Controlled by 2/ more genes (2/ more alleles

Directional Selection

Food becomes scarce.

Low mortality, high fitness

High mortality, low fitness

NATURAL SELECTION ON POLYGENIC TRAITS: 3 MODELS

Section 16-2

Favors traits at 1 extreme of a range of traits

Birth Weight

Selection against both

extremes keep curve narrow and in same

place.

Graph of Stabilizing SelectionSection 16-2

Stabilizing SelectionIndividuals with the most common trait are most adapted, while individuals who differ from the norm are poorly adapted.

Disruptive Selection

Largest and smallest seeds become more common.

Beak Size

Population splits into two subgroups specializing in different seeds.

Beak Size

Graph of Disruptive Selection

Section 16-2

When both extreme phenotypes are favored by natural selection

Balancing SelectionNatural selection acts in opposite directions

*** “Heterozygote Advantage”- ind who is heterozygous for a particular gene has a greater fitness than a homozygous ind

EX: Distribution of sickle-cell allele coincides with the occurrence of malaria

SS Normal hemoglobin

ss Sicke-cell disease

Ss- codominance (protects against malaria)

GENTIC DRIFT: A RANDOM CHANGE IN ALLELE FREQUENCY

• IN SMALL POPULATIONS, INDIVIDUALS THAT CARRY A PARTICULAR ALLELE MAY LEAVE MORE DESCENDANTS THAN OTHER INDIVIDUALS, JUST BY CHANCE. OVER TIME, A SERIES OF CHANCE OCCURRENCES OF THIS TYPE CAN CAUSE AN ALLELE TO BECOME COMMON IN A POPULATION.

• FOUNDER EFFECT: A SITUATION IN WHICH ALLELE FREQUENCIES CHANGE AS A RESULT OF THE MIGRATION OF A SMALL SUBGROUP OF A POPULATION.

Sample of Original Population

Founding Population A

Founding Population B

Descendants

Genetic DriftSection 16-2

In small populations, an allele can become more or less common by chance (explain how allele frequencies can fluctuate unpredictably from 1 gen to the next)

Descendants

FOUNDER EFFECT:2 small groups from a large, diverse population could produce new populations that differ from the original population

Descendants

EVOLUTION VERSUS GENETIC EQUILIBRIUM

HARDY-WEINBERG PRINCIPLE: ALLELE FREQUENCIES IN A POPULATION WILL REMAIN CONSTANT AS LONG AS FIVE CONDITIONS (FACTORS) REMAIN CONSTANT. GENETIC EQUILIBRIUM IS REACHED. (IS THE POPULATION EVOLVING?)

5 CONDITIONS REQUIRED TO MAINTAIN GENETIC EQUIIBRIUM1. RANDOM MATING

- Select mates w/o bias2. LARGE POPULATION

- Genetic drift does not affect large pops3. NO MOVEMENT INTO OR OUT OF THE POPULATION

- no intro of new allele4. NO MUTATION

- no new allele introduced5. NO NATURAL SELECTION

- No phenotype can have selective advantage

DOES THIS EVER HAPPEN?????

• In 1908, Hardy and Weinberg independently demonstrated that DOMINANT ALLELES DO NOT REPLACE RECESSIVE ALLELES IN A POPULATION!

HARDY-WEINBERG EQUATION

You have sampled a population in which you know that the percentage of the homozygous recessive genotype (aa) is 36%. Using that 36%, calculate the following:

The frequency of the "aa" genotype.

The frequency of the "a" allele.

The frequency of the "A" allele.

The frequencies of the genotypes "AA" and "Aa."

The frequencies of the two possible phenotypes if "A" is completely dominant over "a."

• FREQUENCY OF aa GENOTYPE: 36% (GIVEN)

• FREQUENCY OF a ALLELE:The frequency of aa is 36%, which means that q2 = 0.36, by definition. If q2 = 0.36, then q = 0.6, again by definition. Since q equals the frequency of the a allele, then the frequency is 60%.

• The frequency of the "A" allele. Answer: Since q = 0.6, and p + q = 1, then p = 0.4; the frequency of A is by definition equal to p, so the answer is 40%.

• The frequencies of the genotypes "AA" and "Aa." Answer: The frequency of AA is equal to p2, and the frequency of Aa is equal to 2pq. So, using the information above, the frequency of AA is 16% (i.e. p2 is 0.4 x 0.4 = 0.16) and Aa is 48% (2pq = 2 x 0.4 x 0.6 = 0.48).

• The frequencies of the two possible phenotypes if "A" is completely dominant over "a." Answers: Because "A" is totally dominate over "a", the dominant phenotype will show if either the homozygous "AA" or heterozygous "Aa" genotypes occur. The recessive phenotype is controlled by the homozygous aa genotype. Therefore, the frequency of the dominant phenotype equals the sum of the frequencies of AA and Aa, and the recessive phenotype is simply the frequency of aa. Therefore, the dominant frequency is 64% and, in the first part of this question above, you have already shown that the recessive frequency is 36%.

AS NEW SPECIES EVOLVE (SPECIATION), POPULATIONS

BECOME REPRODUCTIVELY ISOLATED FROM EACH OTHER.Section 16-3

results from

which include

produced by produced byproduced by

which result in

Reproductive Isolation

Isolating mechanisms

Behavioral isolation Temporal isolationGeographic isolation

Behavioral differences Different mating timesPhysical separation

Independentlyevolving populations

Formation ofnew species

Section 17-4

Flowchart

that are

can undergo can undergo can undergo can undergo can undergo

in underunderform inin

Species

Unrelated Related

Inter-relationshiops

Similar environments

Intense environmental

pressure

Small populations

Different environments

Coevolution Convergent evolution

ExtinctionPunctuated equilibrium

Adaptive radiation

a. Divergent evolution when 2/ more species originate from a common ancestor

Ex: flipper of whale and limb of human

b. Convergent evolution process by which unrelated organisms come to resemble each other

Ex: torpedo shape of shark and penguin/ wing of insect and bat

c. Coevolution process by which 2 species evolve in response to changes in each other over time

EVOLUTION/POPULATION GENETICS CH. 15-16. SOME INFLUENCES ON DARWIN’S THOUGHT LAMARCK MALTHUS LYELL...

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