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Natural Selection
Define the term evolution.What comes to mind when you hear the
term evolution?
Pre-discussion Questions:
1. What is genetic recombination? 2. What is variation? 3. Name the 3 levels of mutations:
Population
A group of organisms of one species that interbreed and live in the same place at the same time (e.g. deer population).
Gene Pool
The total number of genes of every individual in an interbreeding population.A large gene pool indicates high genetic diversity, increased chances of biological fitness, and survival. A small gene pool indicates low genetic diversity, reduced chances of acquiring biological fitness, and increased possibility of extinction.
Gene Pool
Gene pool increases when mutation occurs and survives. Gene pool decreases when the population size is significantly reduced (e.g. famine, genetic disease, etc.). Some of the consequences when gene pool is small are low fertility, and increased probability of acquiring genetic diseases and deformities.
Discussion:
The 4 Ways that DNA can Change Genetic Recombination:
Crossing Over Independent Assortment of Homologous
Chromosomes (2n) Fertilization Mutations (Genes, Nucleotides, Non-disjunction)
EvolutionA genetic change (within the gene pool) in
a population over time. Must be a change to the DNA
Individual must reproduce to change the gene pool.Therefore those who reproduce the most will “direct” Evolution.
The change is caused by natural selection
Important Scientists
1798 - Malthus – Essay on Population Control.1809 – Lamarck – Use and Disuse
(Has been DISPROVED!!!!!!)Gene changes are random and not thought out
Organisms cannot thoughtfully change their DNA
If you work out really hard,Will you pass that on to yourOffspring?
Important Scientists
1858- Wallace – coined Natural Selection1858 – Darwin – Published Origin of Species.
Charles Darwin
NaturalistSailed on the Beagle
Studied variationOn Galapagos Islands
Continued his study & wrote Origin of SpeciesBook describing the principles of Natural Selection.
Trip of a Life Time
1831-183622 years old!
(a) Cactus eater. The long,sharp beak of the cactusground finch (Geospizascandens) helps it tearand eat cactus flowersand pulp.
(c) Seed eater. The large groundfinch (Geospiza magnirostris)has a large beak adapted forcracking seeds that fall fromplants to the ground.
(b) Insect eater. The green warbler finch (Certhidea olivacea) uses itsnarrow, pointed beak to grasp insects.
Beak variation in Galapagos finches
Darwin had studied Selective Breeding of animals & crops
Breed parents with traits you wantLike Long hair dogs
for living in coldor good milk cows
This is called Artificial Selection
Around 650 AD, startedCross breeding varietiesTo get the seedlessOnes we eat today !
Natural SelectionA genetic change in a population that occurs when organisms with favorable variations for a particular environment survive and pass on the trait to the next generation.
*** Survival of the fittest
Which of these is the fittest?
What does fittest mean?Fitness refers to an organisms ability to reproduce and pass its genetic code to offspring in their environment.
• The more offspring the more fit the organism
• Combination of physical traits & behaviors.
4 Natural Selection Principles:1. There is a variation within the
population.2. Some of the variations are favorable
Allows organisms to survive better than others in THAT environment
3. There is a struggle for existenceMore individuals are produced than live to reproduce
4. Those that survive have the favorable variation and REPRODUCE.
The next generation has the favorable trait Traits are GENETIC = In DNA
Variation and allele frequencies
Biological sciences definition of evolution:
The sum total of the genetically inherited changes of a population’s gene pool
Variation and allele frequencies
The effects of evolution are felt by individuals but it is the population as a whole that actually evolves
Variation and allele frequencies
Evolution is simply a change in the allele frequency of the gene pool in a population over time
Hardy Weinberg Equilibrium
Godfrey Hardy and Wilhelm Weinberg concluded that gene pool frequencies are inherently stable but that evolution should be expected in all populations all the time
Hardy Weinberg Equilibrium The hardy Weinberg equilibrium model suggests that evolution will NOT occur if the following 5 conditions are met
1. No Mutations (no changes in alleles)
2. No Natural selection (all alleles/traits are favored)
3. The population is infinitely large
4. All mating is totally random
6. No migration into or out of the population
Hardy Weinberg Equilibrium If no mechanisms of evolution are acting on a population, evolution will not occur and the gene pool (allele) frequencies will not change – it will remain constant
. This is called genetic equilibrium
Hardy Weinberg EquilibriumIt is highly unlikely that any of these seven
conditions will happen in the real world and evolution (DNA change) is inevitable.
Evolution is the result of a disruption in genetic equilibrium
Variations
The differences between individual members of a population.
Peppered Moths – Allele changes in population
Dark vs. light variants
Year % dark % light1848 5 951895 98 21995 19 81
VariationsFavorable variations are often caused by genetic recombination.
1.Crossing Over
2.Random Assortment of Homologous Chromosomes
3.Fertilization
4.Mutation
Changes caused by mutations in DNA that allows the organism to better survive are called:
Advantageous Mutations
VariationsWhen these variations occur there
will be more offspring from these organism because of the survival rate.
This slowly changes the species over time.
Based upon generational time.
AdaptationsAn inherited trait that increases a population’s chances of survival and reproduction in a particular environment
AdaptationsTypes of adaptations
1. Structural: Used for defense against predators
Structural AdaptationsExamples:Defense - Horn, Thorn, Armor, PoisonMimicry and Camouflage to hide
Adaptations
2. Physiological: Changes in metabolic processes for survival.
Physiological Adaptation
Examples:Resistance to chemicals such
as antibiotics.Pest resistance
to pesticides
Patterns/Types of Natural Selection
Based on the favorable adaptations and variations within a population,
There are patterns of change that populations will follow based upon the genetic variation present in the
population.
Normal DistributionGet a bell shaped curve of variation
But Environmental Stress can favor certain phenotypes
Patterns of Evolution (changes in allele frequency)
Natural Selection (3 patterns) 1. Stabilizing Selection 2. Disruptive Selection 3. Directional Selection
Artificial Selection Example: Dog Breeding
1. Stabilizing Selection: this type of natural selection favors the average individuals within the population. The extreme phenotypes in the population are selected against.
Natural Selection
1. Stabilizing Selection: this type of natural selection favors the average individuals within the population. The extreme phenotypes in the population are selected against.
Natural Selection
Natural Selection 2. Disruptive Selection: This type of natural selection selects for the extreme phenotypes in a population. The trait selected against is the average phenotype.
3. Directional Selection: This type of natural selection is where one extreme phenotype of the population is favored. The other extreme is selected against within the population
Natural Selection
Disruptive
Artificial Selection
Human interference to breed organisms (cats, dogs, plants etc.) with desirable traits.
Controlling the population through selective breeding
Evidence for EvolutionThe Keys to the Past & the Future are often what we know in the Present ! How is the earth changing RIGHT now?
…. New islands by volcanos, deserts growing
How do we know animals have not always been the same?
….. Fossils,
Banana fossils in Oregon,
fish fossils in Idaho desert
Evidence for EvolutionThe Keys to the Past & the Future are often what we know in the Present !
Evidence for EvolutionThe Keys to the Past & the Future are often what we know in the Present !
4 main pieces of evidence for evolution 1. Fossils
2. Embryological Comparisons
3. Anatomical Comparisons
4. Genetic Comparisons
Fossils 2 ways to date fossils
1. Relative dating
Comparing fossils to different rock layers in the sediment.
The deeper the fossil, the older the specimen
2. Radioactive dating Testing the half life of chemicals (mainly carbon) to date the materials
Embryological Comparisons
A comparison of vertebrate embryos to support the theory of evolution
Early embryos
look similar
Humans have
Gill pouches
Anatomical Comparisons
A. Vestigial Structures– structures that have no use to the organism any more
Example: Tail bone, whale pelvis, snake legs
Anatomical Comparisons
B. Homologous structures– similar structures seen in organisms with similar ancestors
Example: Fore arms of various mammals including whales, horses and humans
Anatomical Comparisons
C. Analogous structures – structures that are similar in function but not in form
Example: A bat wing and an insect wing…. …both exist in an airborne environment
Genetic Comparisons
The strongest piece of evolution that scientists have today
Uses the genetic code of various organisms to show the relationships genetically
Genetic Comparison
More base sequences the same, closer you are related !
Oldest: ATCCGTAATC
Order the closest related to furthest:
A. ACCCTTACGC
B. ATCGGTACTC
C. ACCCTTACGT
21 most alike3 most different
Time of Evolution
Two general theories about how fast evolution happens
Remember it occurs in generational time
1. Punctuated Equilibrium
2. Gradualism
Punctuated Equilibrium
A model of evolution in which short periods of drastic change in species, including mass extinctions and rapid speciation are separated by long periods of little or no change
Gradualism
A model of evolution in which gradual change over a long period of time leads to biological diversity
Rate of SpeciationDoes speciation happen gradually or rapidly
Charles DarwinCharles Lyell
Stephen Jay GouldNiles Eldredge
Gradualism Punctuated Equilibrium
rapid bursts of change mixed with long periods
of little or no change
gradual accumulation of small changes over long time
Causing a new species: Speciation
Speciation occurs when the DNA changes enough to create a new species
Species: a group of organisms that live in the same place and can freely interbreed AND produce fertile offspring
2 general causes of speciation
1. Population Isolation a. Reproductive
b. Geological
2. Genetic Drifta. Bottle Neck
b. Founders Effect --Happens to small populations
Population Isolation
a. Reproductive Isolation The inability of members of a population to successfully interbreed with members of another population or related species because of :
Mating TimeMating Rituals Sexual Selection (ex. Why birds are brightly colored)
Population Isolation
b. Geographic Isolation Caused by geographical barriers or any physical barrier that would isolate a population of individuals from its parent population
Ex. Mountains, rivers, canyons, etc.
Genetic Drift
A. Bottle Neck Effect Where a population is affected dramatically by a disaster or reproduction failure.
Only a few organisms survive to reproduce
Genetic Drift
B. Founders Effect When a small group of organisms move from one area to another, leaving the parent population and create a change in a new genome.
Patterns of Evolution
A. Divergent EvolutionAdaptative Radiation
B. Co-Evolution
C. Convergent
Evolution
Patterns of Evolution
A. Divergent Evolution When a population becomes separated by a geographical barrier and evolve separately.
Evolve from a common ancestorAdaptive Radiation:
• Many species evolve from a common ancestor and have a lot of room to occupy.
• Example: Finches
Phylogenetic trees
Like a tree
Adaptive Radiation & Darwin’s Finches
Adaptive Radiation & Darwin’s Finches
Patterns of Evolution
Co-Evolution When two species interact they evolve traits
together to continue that relationship.Symbiotic Relationships
Example: Predation, Mutualism, Parasitism
Coevolution
Patterns of Evolution
Convergent Evolution Two species who are not
related evolve similarities
in appearance OR
behavior
Example: bats + birds + insectAll have evolved in an airtime
environment
Have Analogous Structures, convergent evolution.
Similar function, but different structures
Convergent EvolutionOrganisms evolve into similar body forms
due to similar ecosystemsNot Related – No common ancestors
Summary
Natural Selection is what causes evolution and changes in organisms over time.
That natural selection tends to act on Phenotypes of individuals and affect the resulting genotypes!