Natural Selection is the Mechanism of EvolutionObjectives:

1. Summarize Darwin’s theory of natural selection.

2. Compare and contrast artificial selection w/ natural selection.

3. Relate pesticides resistance in insects to natural selection.

Vocab.

Population

Variation

Artificial Selection

Evolution occurs in POPULATIONS, NOT INDIVIDUALS

Population:

Group of individuals of the same species living in the same area at the same time.

Evolutionary changes occur as a result of a CHANGE IN THE FREQUENCY OF ALLELES IN A POPULATION.

NATURAL SELECTION selects favorable alleles!

DARWIN’S Natural Selection is based on 2 observations! 1. All species tend to produce EXCESSIVE # of

OFFSPRING; MORE than NATURE CAN SUPPORT /Resources. <Malthus>

RESULT = STRUGGLE FOR SURVIVAL; Small % survive to reproduce.

2. There is VARIATION (traits) among indviduals in a population.

Variation is due to different alleles (genotypes) producing different phenotypes

Natural Selection & Evolution

Individuals w/ traits (variations) favored by their environment will survive & reproduce more offspring. Over many generations, the favorable traits will be more common.

Adaptations = traits favored by environment.

Artificial Selection Encourages Darwin

Artificial Selection: selective breeding of domesticated plants and animals to produce offspring w/ traits desired by humans.

Like Natural Selection … it can change the gene pool and change a species.

Unlike Natural Selection … PEOPLE select traits (not nature)

Natural Selection & Pesticide Resistance in Insects

Some insects have natural resistance (mutation in genes).

Resistant insects survive and pass on resistance to offspring.

Over generations, resistant insects b/cm more common.

SummarySummaryProcess of Natural SelectionProcess of Natural Selection

(S.N.A.S.D.)(S.N.A.S.D.)• Struggle for Existence:Struggle for Existence: Organisms generally have more

offspring than resources can support• Natural Variation:Natural Variation: Even within a species there will be

distinct differences between individual organisms• Adaptation:Adaptation: Some variations provide individuals with an

advantage that increases their chances of survival.• Survival of the Fittest:Survival of the Fittest: Those with the adaptations are

more likely to survive and reproduce• Descent with Modification:Descent with Modification: Genes for the beneficial

adaptations are passed on and the trait becomes increasingly more common in each new generation of the species

Microevolution & Changes in the Gene Pool

Objectives:

1. Explain the significance of gene pools in understanding evolution.

2. Tell how the genetic drift, gene flow, mutation, and natural selection contribute to changes in the gene pool.

3. Explain what is meant by fitness.

Vocab.

Gene pool

Hardy-Weinberg equilibrium

Genetic drift

Gene flow

Fitness

Darwin didn’t know about genes… we do. Natural Selection acts on variations

(alleles) in the gene pool. Result = Evolution

Gene Pool

All of the alleles in all of the individuals that make up a population; Healthy gene pools have variation!

Evolution occurs when there is any change in the gene pool.Change in Gene Pool = Change in allele

frequencies

Microevolution = change in frequency of alleles fr. generation to generation.

Genetic Drift

Change in gene pool due to RANDOM CHANCE. (instead of Natural Selection)

Microevolution: What can cause a population to evolve?

Five Fingers of Evolution

1.Pinky: Chance events SHRINK popluation.(bottleneck effect or Founders); New population is established from small gene pool that may or may not represent allele freq. in original population.

2.Ring: Mating/Marriage is not random (Mates are picked based on certain characteristics); some alleles are favored.

3.Middle: Mutations occur and add new alleles.

4.Pointer: Movement (migration of individuals) into or out of an area affects allele freq.

5.Thumb: Natural selection – nature selects traits that are favorable = adaptations (like opposable thumbs)

Change in Gene Pool: Chance events SHRINK gene pool.

Pinky: Population shrinks (bottleneck effect or Founders); New population is established from small gene pool that may or may not represent allele freq. in original population.

Bottleneck EffectBottleneck EffectDisaster drastically reduces population (& gene pool)Disaster drastically reduces population (& gene pool)Few individuals repopulate. Few individuals repopulate. New population lacks genetic variation.New population lacks genetic variation.

Pinky: Chance SHRINKS population; New population is established from small gene pool that may or may not represent allele freq. in original population.

Founder’s Effect

Change in Gene Pool Ring: Mating/Marriage is not random (Mates are picked based on certain characteristics); some alleles are favored.

Change in Gene Pool Middle: Mutations occur and add new alleles

Sickle cell trait, lactose tolerance, etc.

Change in Gene Pool

Thumb: Natural selection – nature selects traits that are favorable = adaptations (like opposable thumbs)

Gene Flow: Exchange of genes b/w populations. Reduces genetic differences b/w populations.

Change in Gene Pool Pointer: Movement (migration of individuals) into or out of an area affects allele freq (Gene Flow)

Contributing to the Gene Pool = FITNESS

Fitness = Contribution an individual makes to the gene pool compared to other individuals.

You don’t have to be the “Fittest” … you just have to survive & contribute genes to next generation

Genetic Equilibrium= allele frequencies are not changing from one generation to the next•Hardy-Weinberg theory: a population is in genetic equilibrium if the following conditions are met simultaneously:

– Large population size– Random mating– No mutations– No migration– No natural selection

Hardy Weinberg Equilibrium Tutorial•http://www.phschool.com/science/biology_place/labbench/lab8/hardwein.html

Nat. Selection & Sickle Cell Disease

African populations have high incidence of sickle cell.

Carriers of sickle cell have resistance to malaria.

Malaria = major cause of infant death in Africa.

Carriers (heterozygous) have advantageous adaptation.

Higher incidence of sickle allele remains in African population

Natural Selection: Selected for Sickle cell allele b/c it provides an advantage (Resistance to Malaria!).

Natural Selection & Antibiotic Resistance Some bacteria have natural

resistance to antibiotics (mutation, share by conjugation)

Some survive treatment --> pass resistance genes on -> alleles for resistance b/cm more common.

NOT COMPLETING COURSE OF ANTIBIOTICS CAN INCREASE RESISTANCE.