Evolution

Chapters 22-25

Evolution

Changes in populations, species, or groups of species.Variances of the frequency of heritable traits

that appear from one generation to the next.

2 Areas of Evolutionary Study

Microevolution Details of how

populations of organisms change.

Generation to Generation

New species origninate

Macroevolution Patters of change in

groups of related species.

Broad period of geologic time

Patterns determine phylogeny.

The evolutionary relationships among species and groups of species

Agree or Disagree

For each of the following statements decide if you agree that this is how evolution occurs or disagree.

After you have agreed or disagreed choose 2 agree statements and site examples and 2 disagree statements and site examples.

Lamarck

3 ideas for evolution:Use and Disuse Inheritance of acquired characteristicsNatural Transformation of species

Use and Disuse

How body parts of organisms can develop with increased usage, while unused parts weaken.

Inheritance of Acquired Characteristics

Described how body features acquired during the lifetime of an organism could be passed on to offspring.

Natural Transformation of Species

Organisms produced offspring with changes, transforming each subsequent generation into a slightly different form toward some ultimate higher order of complexity.

Species did not become extinct nor did they split and change into two or more species.

Evidence for Evolution

PaleontologyBiogeographyEmbryologyComparative AnatomyMolecular Biology

overproductioncompetitionvariation

adaptationNatural

Selectionspeciation

•More organisms are born than needed to maintain the population

competitionvariation

adaptationNatural

Selectionspeciation

Organisms compete for limited natural resources such as food, water, shelter and space.

variationadaptation

Natural Selectionspeciation

Organisms within a population vary. Variation is heritable.

adaptationNatural

Selectionspeciation

Any inherited trait that increases the chances of survival. Fitness is determined by the environment.

Natural Selectionspeciation

•Individuals with favorable variations (adaptations) are more likely to survive and pass on these traits to their offspring

• “Survival of the Fittest”

Evolution and Speciation

•Favorable variations (adaptations) gradually accumulate and unfavorable variations disappear over many generations

•Eventually this leads to a new species

4 Different types of Selection

Stabilizing SelectionDisruptive SelectionDirectional SelectionSexual SelectionArtificial Selection

Sources of Variation

MutationsSexual ReproductionDiploidyOutbreedingBalanced Polymorphism

Mutations

Raw material for new variation.Invents new genes that were never in

the gene pool before.

Sexual Reproduction

Creates individuals with new allele frequencies.

Genetic Recombination- 3 eventsCrossing Over Independent Assortment of HomologuesRandom Joining of Gametes

Diploidy

The presence of 2 copies of each chromosome in a cell.

Recessive alleles are hidden in the gene pool.

Outbreeding

Mating of unrelated partners.Increases the possibility of mixing

different alleles and creating new combinations.

Balanced PolymorphismMaintenance of different phenotypes in a

population.Heterozygote Advantage

The heterozygote condition bears a greater selective advantage. (Sickle Cell in Africa)

Hybrid Vigor/ heterosisSuperior quality of offspring resulting from crosses

between 2 different inbred strains of plants. Frequency-dependent selection

Least common phenotypes have a selective advantage. Predator mimicking prey.

Causes of Changes in Allele Frequencies

Natural SelectionMutationsGene FlowGenetic DriftNonrandom Mating

Gene Flow

The introduction or removal of alleles from the population ImmigrationEmigration

Genetic Drift

A random increase or decrease of alleles.2 Types

Founder Effect Alleles in a group of migrating individuals are not the

same as that of the origin population.Bottleneck

Population undergoes a dramatic decrease in size due to a natural catastrophe.

Nonrandom Mating

Individuals choose mates based upon their particular traits. InbreedingSexual Selection

How do we know evolution is occuring?

Hardy-Weinberg5 Conditions for Hardy-Weinberg

Equilibrium (evolution is not happening)All traits are selectively neutralMutations do no occurNo gene flowNo genetic driftRandom mating

Genetic Equilibrium Determination

Allele frequencies for each allelep is for the dominant alleleq is for the recessive allele

Frequency of homozygotesp2 is for the homozygous dominantq2 is for the homozygous recessive

Frequency of heterozygotespq + qp = 2pq

Equations

p + q= 1p2 + 2pq + q2 = 1

Example Problem

Suppose a plant population consists of 84% plants with red flowers and 16% with white flowers. Assume the red allele (R) is dominant to the white allele (r).

Do Hardy-Weinberg conditions meet any population?

NO!Why bother learning it?

Starting pointFurther investigation as to which condition is

being violatedMechanisms of evolution

Speciation

SpeciesSpeciation

The formation of a new species by one of 4 processes

AllopatricSympatricSympatric by PolyploidyAdaptive Ratiation

Allopatric Speciation

Population is divided by a geographic barrier.

Barrier creates isolation of breeding.Species continue to evolve by natural

selection (if environments are different), mutation, genetic drift.

Sympatric Speciation

The formation of a species without the presence of a geographic barrier.Balanced Polymorphism

Camouflage and MimicryHybridization

Sympatric Speciation by Polyploidy

The posession of more than the normal two sets of chromosomes (2n).

Polyploidy occurs as a result of non-disjunction of all chromosomes during meiosis.

A tetraploid can occur when two diploid gametes come together.

Reproductive Isolation thus speciation

Adaptive Radiation

Rapid evolution from a single speciesAdapts to geographic or ecological

conditions.Darwin’s Finches

Maintaining Reproductive Isolation

Necessary for speciationPrezygotic Isolating MechanismsPostzygotic Isolating Mechanisms

Prezygotic Isolating Mechanisms

Habitat IsolationTemporal IsolationBehavioral IsolationMechanical IsolationGametic Isolation

Postzygotic Isolating Mechanisms

Hybrid InviabilityHybrid SterilityHybrid Breakdown

Patterns of Microevlution

Divergent EvolutionConvergent EvolutionParallel EvolutionCoevolution

JigsawGroups of 4, 1-2 sentence summary.Picture or graph of evolution

Patterns of Macroevolution

Phyletic GradualismPunctuated Equilibrium

Phyletic Gradualism

Gradual Accumulation of small changes.

Fossil evidence provides snapshots of the evolutionary process.

Punctuated Equilibrium

Long periods of no evolution “stasis” followed by quick bursts of evolution.

The Earth and its atmosphere formed.

Consisted of CO, Carbon dioxide, hydrogen gas, nitrogen gas, water, sulfur, and hydrochloric acid.

Little or no oxygen gas.

The primordial seas formed

The earth cooled, gases condensed to produce seas consisting of water and minerals.

Complex molecules were synthesized.

Miller-Urey Experiment

Oranic molecules were formed from inorganic molecules with help from energy.

Polymers and self-replicating molecules were synthesized.

Monomers combined to form polymers.Proteinoids

Abiotically produced polypeptides

Organic molecules were concentrated and isolated into protobionts.

ProtobiontsCell precursors.Able to carry out chemical processesNot able to reproduce.

Microspheres and coacervates

Primitive heterotrophic prokaryotes formed.

Heterotrophs formed to take in materials.Natural selection

Primitive autotrophic prokaryotes were formed.

Mutation for an autotroph to be formed.Produces oxygen as a product of

chemical processes.

Oxygen and the ozone layer formed and abiotic chemical evolution ended.

Oxygen released in the atmosphere.Ozone layer made.UV light was filtered.Major source of energy was eliminated.

Eukaryotes formed

Endosymbiotic Theory