EVOLUTION/POPULATION GENETICS CH. 15-16. SOME INFLUENCES ON DARWIN’S THOUGHT LAMARCK MALTHUS LYELL...
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Transcript of EVOLUTION/POPULATION GENETICS CH. 15-16. SOME INFLUENCES ON DARWIN’S THOUGHT LAMARCK MALTHUS LYELL...
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
Lamarck’s Theory of Evolution
• Idea called Law of Use and Disuse
• If a body part were used, it got stronger
• If body part NOT used, it deteriorated
Lamarck’s Theory of Evolution
• 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
Coypu
Geographic Distribution of Living SpeciesSection 15-3
Beaver
Muskrat
Beaver andMuskrat
Coypu
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
black
36% homozygous
brown
16% homozygous
black
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!!!!!!
Fre
qu
ency
of
Ph
eno
typ
e(%
)100
80
60
40
20
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
Fre
qu
enc
y o
f P
hen
oty
pe
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.
Key
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
Key
Per
cen
tag
e o
f P
op
ula
tio
n
Birth Weight
Selection against both
extremes keep curve narrow and in same
place.
Graph of Stabilizing SelectionSection 16-2
Low mortality, high fitness
High mortality, low fitness
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.
Nu
mb
er o
f B
ird
sin
Po
pu
lati
on
Beak Size
Population splits into two subgroups specializing in different seeds.
Beak Size
Graph of Disruptive Selection
Nu
mb
er o
f B
ird
sin
Po
pu
lati
onKey
Low mortality, high fitness
High mortality, low fitness
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)
Sample of Original Population
Founding Population A
Founding Population B
Descendants
Genetic DriftSection 16-2
FOUNDER EFFECT:2 small groups from a large, diverse population could produce new populations that differ from the original population
Sample of Original Population
Founding Population A
Founding Population B
Descendants
Genetic DriftSection 16-2
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
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