Evolution of PopulationsEvolution of Populations

Genes & Variation--What causes Genetic Variation

in Populations?

Genes & Variation--What causes Genetic Variation

in Populations?

Mutations Gene Shuffling Crossing Over

Mutations Gene Shuffling Crossing Over

Gene Pools and Allele Frequencies

Gene Pools and Allele Frequencies

What is a gene pool?

(All of the genes and information from all members of a particular species)

What are Allele Frequencies?

(How many times that allele occurs in the gene pool---eg. Black fur B = 40%)

What is a gene pool?

(All of the genes and information from all members of a particular species)

What are Allele Frequencies?

(How many times that allele occurs in the gene pool---eg. Black fur B = 40%)

Sources of Genetic Variation

Sources of Genetic Variation

Mutations

Gene Shuffling -- 23 chromosomes can produce 8.4 million different combinations of genes

Crossing Over -- Further, “Shufffles the deck” Producing more combinations

Mutations

Gene Shuffling -- 23 chromosomes can produce 8.4 million different combinations of genes

Crossing Over -- Further, “Shufffles the deck” Producing more combinations

New Combinations of Alleles

New Combinations of Alleles

Single Genes & Polygenic TraitsSingle Genes & Polygenic Traits

Single Gene Traits

AA, Aa, aa

Polygenic TraitsAABBCC, AaBbCc(3 Genes)-------->

Single Gene Traits

AA, Aa, aa

Polygenic TraitsAABBCC, AaBbCc(3 Genes)-------->

Natural Selection on Single gene Traits

Natural Selection on Single gene Traits

Can Lead to changes in the Allele Frequencies and

consequently----> Evolution

Example--Black and brown lizards

Red (mutation) doesn’t survive as well on a dark background

Can Lead to changes in the Allele Frequencies and

consequently----> Evolution

Example--Black and brown lizards

Red (mutation) doesn’t survive as well on a dark background

Natural Selection on Polygenic traits

Natural Selection on Polygenic traits

Can affect the distributions of phenotypes in 3 ways---

1) Directional selection 2) Stabilizing selection 3) disruptive selection

Can affect the distributions of phenotypes in 3 ways---

1) Directional selection 2) Stabilizing selection 3) disruptive selection

Stabilizing Selection-->Selects for the

average form

Stabilizing Selection-->Selects for the

average form

Directional Selection-->Selects for an

extreme

Directional Selection-->Selects for an

extreme

Diversifying Selection--Selects for both

extremes

Diversifying Selection--Selects for both

extremes

Natural Selection on Single Gene Traits

Natural Selection on Single Gene Traits

Genetic DriftGenetic Drift

Genetic Drift in The AmishGenetic Drift in The Amish

Example of Genetic DriftExample of Genetic Drift

An example is the frequency of total color-blindness among the inhabitants of Pingelap, an island in Micronesia. In approximately 1775, a typhoon reduced the population of the island to only 20. Among survivors, one of them was heterozygous for achromatopsia.

An example is the frequency of total color-blindness among the inhabitants of Pingelap, an island in Micronesia. In approximately 1775, a typhoon reduced the population of the island to only 20. Among survivors, one of them was heterozygous for achromatopsia.

After few generations, the prevalence of achromatopsia is 5% of population and 30% as carriers (by comparison, in the United States, only 0.003% of the population has complete achromatopsia.

After few generations, the prevalence of achromatopsia is 5% of population and 30% as carriers (by comparison, in the United States, only 0.003% of the population has complete achromatopsia.

Amish polydactyl (6 fingered) Achondroplastic Dwarf

Amish polydactyl (6 fingered) Achondroplastic Dwarf

Evolution vs. Genetic Equilibrium

Evolution vs. Genetic Equilibrium

Evolution = Genetic Change What does Genetic Equilibrium

= ?

NO CHANGE ! POPULATIONS WOULD STAY THE SAME, “IN EQUILIBRIUM”

Evolution = Genetic Change What does Genetic Equilibrium

= ?

NO CHANGE ! POPULATIONS WOULD STAY THE SAME, “IN EQUILIBRIUM”

Remember the Blue-footed Booby?

Remember the Blue-footed Booby?

Hardy-Weinberg Equilibrium

Hardy-Weinberg Equilibrium

Conditions for Equilibrium (Hardy--

Weinberg)

Conditions for Equilibrium (Hardy--

Weinberg) What would the conditions

have to be for no change? ie. No Evolution

1. No mutation 2. No natural selection 3. Large population 4. All members of the

population breed

What would the conditions have to be for no change? ie. No Evolution

1. No mutation 2. No natural selection 3. Large population 4. All members of the

population breed

5. Random mating 6. everyone produces the

same number of offspring 7. no migration in or out of

the population

5. Random mating 6. everyone produces the

same number of offspring 7. no migration in or out of

the population

SpeciationSpeciation

Isolating MechanismsIsolating Mechanisms

GEOGRAPHIC REPRODUCTIVE

BEHAVIORAL TEMPORAL

GEOGRAPHIC REPRODUCTIVE

BEHAVIORAL TEMPORAL

GEOGRAPHIC ISOLATIONGEOGRAPHIC ISOLATION

Leads to--> Reproductive Isolation

Leads to--> Reproductive Isolation

REPRODUCTIVE ISOLATIONREPRODUCTIVE ISOLATION

Species can no longer reproduce with the, “New” species

Eg. 2 species of fruitflies

Guava or Banana?

The evolution of different mating location, mating time, or mating rituals:

Species can no longer reproduce with the, “New” species

Eg. 2 species of fruitflies

Guava or Banana?

The evolution of different mating location, mating time, or mating rituals:

TEMPORAL ISOLATIONTEMPORAL ISOLATION

Mating at different times of the year

Other frogs-- Green frogs-->

April Bullfrogs--> June

Mating at different times of the year

Other frogs-- Green frogs-->

April Bullfrogs--> June

BEHAVIORAL ISOLATIONBEHAVIORAL ISOLATION

Courtship rituals--(Dances, Flashes,)

Food preferences

Courtship rituals--(Dances, Flashes,)

Food preferences

Firefly--> FlashesFirefly--> Flashes

Misconception: “Natural selection gives organisms

what they ‘need.’ ”

Misconception: “Natural selection gives organisms

what they ‘need.’ ”