SpeciationSpeciationGenetic Equilibrium

Disruption of Genetic EquilibriumFormation of Species

Genetic EquilibriumDisruption of Genetic Equilibrium

Formation of Species

Genetic Equilibrium

Genetic Equilibrium

• Species: a group of individuals that look similar and whose members are capable of producing fertile offspring in the natural environment

• Species: a group of individuals that look similar and whose members are capable of producing fertile offspring in the natural environment

Morphological Species ConceptMorphological Species Concept

• Morphological Species Concept: the idea that organisms can be classified by differences in their appearance– Using this concept, scientists can readily

communicate about the characteristics, behavior, and relationships of organisms.

– The morphological concept of species is limited because it does not account for the reproductive compatibility of morphologically different organisms.

• Morphological Species Concept: the idea that organisms can be classified by differences in their appearance– Using this concept, scientists can readily

communicate about the characteristics, behavior, and relationships of organisms.

– The morphological concept of species is limited because it does not account for the reproductive compatibility of morphologically different organisms.

Biological Species ConceptBiological Species Concept

• Biological Species Concept: the idea that organisms can be classified by their ability to breed with one another

• Using both the biological and morphological concepts of species, modern scientists have arrived at the current definition of the term species.

• Biological Species Concept: the idea that organisms can be classified by their ability to breed with one another

• Using both the biological and morphological concepts of species, modern scientists have arrived at the current definition of the term species.

Species: a group of individuals that look similar and whose members are capable of producing fertile offspring in the natural environment

Species: a group of individuals that look similar and whose members are capable of producing fertile offspring in the natural environment

Variation of Traits in a PopulationVariation of Traits in a Population

• Population: all the members of a species that live in the same area and make up a breeding group

• Within a population, individuals vary in many observable traits.

• Population: all the members of a species that live in the same area and make up a breeding group

• Within a population, individuals vary in many observable traits.

CaribouPopulationDistribution

Variation is the Raw Material of Natural Selection

Variation of Traits in a PopulationVariation of Traits in a Population

What causes variation in traits?What causes variation in traits?

• Environmental Factors• Heredity

– A difference in genotype usually results in a difference in phenotype.

– Variations in genotypes arise through:• Mutation• Genetic Recombination

– Independent Assortment– Crossing Over

• Environmental Factors• Heredity

– A difference in genotype usually results in a difference in phenotype.

– Variations in genotypes arise through:• Mutation• Genetic Recombination

– Independent Assortment– Crossing Over

Allele Frequencies and Genetic EquilibriumAllele Frequencies and Genetic Equilibrium• Gene Pool: all the genes for all the

traits in a population• Allele Frequency: the percentage

of an allele in a gene pool• Genetic Equilibrium: the condition

in which allele frequencies in a population do not change from generation to generation

• Gene Pool: all the genes for all the traits in a population

• Allele Frequency: the percentage of an allele in a gene pool

• Genetic Equilibrium: the condition in which allele frequencies in a population do not change from generation to generation

Genotypic and Allele FrequenciesGenotypic and Allele Frequencies

Hardy & WeinbergHardy & Weinberg

• Hardy and Weinberg outlined the conditions necessary for genetic equilibrium.

• Hardy and Weinberg outlined the conditions necessary for genetic equilibrium.

Wilhelm WeinbergGodfrey Hardy

Hardy-Weinberg PrincipleHardy-Weinberg Principle

• Hardy and Weinberg outlined the conditions necessary for genetic equilibrium.1. no mutations occur2. individuals neither enter nor leave the population through migration3. the population is large4. individuals mate randomly5. natural selection does not occur

• Hardy and Weinberg outlined the conditions necessary for genetic equilibrium.1. no mutations occur2. individuals neither enter nor leave the population through migration3. the population is large4. individuals mate randomly5. natural selection does not occur

Hardy-Weinberg PrincipleHardy-Weinberg Principle

• If one of these conditions does not hold true, allele frequencies of the population may change. In other words, evolution will occur.

• If one of these conditions does not hold true, allele frequencies of the population may change. In other words, evolution will occur.

Disruption of Genetic

Equilibrium

Disruption of Genetic

Equilibrium

Disruption of Genetic EquilibriumDisruption of Genetic Equilibrium

Evolution occurs when genetic equilibrium is disrupted.

Evolution occurs when genetic equilibrium is disrupted.

1. Mutation1. Mutation

• Mutations affect genetic equilibrium by producing totally new alleles for a trait.

• In addition, mutations can change the frequency of the alleles already present in the gene pool.

• The occurrence of mutation in most alleles is too low to cause major changes in the allele frequencies of an entire population.

• Mutations affect genetic equilibrium by producing totally new alleles for a trait.

• In addition, mutations can change the frequency of the alleles already present in the gene pool.

• The occurrence of mutation in most alleles is too low to cause major changes in the allele frequencies of an entire population.

1. Mutation1. Mutation

2. Migration2. Migration

• Migration: the movement of individual organisms into or out of a population, community, or biome– Immigration: movement of new

individuals into a population– Emigration: departure of individuals

from a population• Gene Flow: the movement of

genes into or out of a population

• Migration: the movement of individual organisms into or out of a population, community, or biome– Immigration: movement of new

individuals into a population– Emigration: departure of individuals

from a population• Gene Flow: the movement of

genes into or out of a population

2. Migration2. Migration

3. Genetic Drift3. Genetic Drift

• Genetic Drift: a shift in allele frequencies in a population due to random events or chance– In small populations, chance can

significantly affect allele frequencies from one generation to the next.

• Genetic Drift: a shift in allele frequencies in a population due to random events or chance– In small populations, chance can

significantly affect allele frequencies from one generation to the next.

3. Genetic Drift3. Genetic Drift

3. Genetic Drift3. Genetic Drift

4. Non-Random Mating4. Non-Random Mating

• If animals chose their mates then certain traits would be selected for over less desirable ones.

• If animals chose their mates then certain traits would be selected for over less desirable ones.

5. Natural Selection5. Natural Selection

• Natural selection is an ongoing process in nature, and is the single most significant factor disrupting genetic equilibrium.

• Natural selection is an ongoing process in nature, and is the single most significant factor disrupting genetic equilibrium.

4 Types of Natural Selection4 Types of Natural Selection1. Stabilizing Selection2. Directional Selection3. Disruptive Selection4. Sexual Selection

1. Stabilizing Selection2. Directional Selection3. Disruptive Selection4. Sexual Selection

Stabilizing SelectionStabilizing Selection

• Stabilizing Selection: a type of natural selection in which the average form of a trait causes an organism to have an advantage in survival and reproduction– The extreme forms of the trait confer a

disadvantage to the organism.– Stabilizing selection is most effective in a

population that has become well adapted to its environment.

– Stabilizing selection is the most common type of NS.

• Stabilizing Selection: a type of natural selection in which the average form of a trait causes an organism to have an advantage in survival and reproduction– The extreme forms of the trait confer a

disadvantage to the organism.– Stabilizing selection is most effective in a

population that has become well adapted to its environment.

– Stabilizing selection is the most common type of NS.

Directional SelectionDirectional Selection

• Directional Selection: a type of natural selection in which the distribution of a trait is shifted toward one of the extremes

• Directional Selection: a type of natural selection in which the distribution of a trait is shifted toward one of the extremes

Disruptive SelectionDisruptive Selection

• Disruptive Selection: natural selection in which individuals with either of the extreme forms of a trait have an advantage in terms of survival and reproduction– The average form of the trait confers

a selective disadvantage to the organism.

• Disruptive Selection: natural selection in which individuals with either of the extreme forms of a trait have an advantage in terms of survival and reproduction– The average form of the trait confers

a selective disadvantage to the organism.

Sexual SelectionSexual Selection

• Sexual Selection: the preferential choice of a mate based on the presence of a specific trait– Sexual selection may be stabilizing,

directional, or disruptive.

• Sexual Selection: the preferential choice of a mate based on the presence of a specific trait– Sexual selection may be stabilizing,

directional, or disruptive.

Formation of Species

Formation of Species

SpeciationSpeciation

• Disruption of genetic equilibrium leads to changes in the gene pool of a population.

• Natural selection causes the most significant genetic changes in a population, however, such changes do not necessarily lead to speciation.

• Speciation: the formation of a new species

• Disruption of genetic equilibrium leads to changes in the gene pool of a population.

• Natural selection causes the most significant genetic changes in a population, however, such changes do not necessarily lead to speciation.

• Speciation: the formation of a new species

Speciation

Speciation

Isolated PopulationsIsolated Populations

• For a new species to arise, either interbreeding of the population of fertile offspring must somehow cease among members of a formerly successful breeding population.– For this to occur, populations or segments of

populations must somehow become isolated.

• Two Forms of Isolation:– Geographic Isolation– Reproductive Isolation

• For a new species to arise, either interbreeding of the population of fertile offspring must somehow cease among members of a formerly successful breeding population.– For this to occur, populations or segments of

populations must somehow become isolated.

• Two Forms of Isolation:– Geographic Isolation– Reproductive Isolation

Geographic IsolationGeographic Isolation

• Geographic Isolation: the physical separation of populations– Examples: population

becomes divided by land or water barrier, colonization of new island, river changes course, highway built across field, etc.

• Geographic Isolation: the physical separation of populations– Examples: population

becomes divided by land or water barrier, colonization of new island, river changes course, highway built across field, etc.

Reproductive IsolationReproductive Isolation

• Reproductive Isolation: the inability of formerly interbreeding organisms to produce offspring– Reproductive isolation can occur

through disruptive selection.

• Reproductive Isolation: the inability of formerly interbreeding organisms to produce offspring– Reproductive isolation can occur

through disruptive selection.

Rates of SpeciationRates of Speciation

• Punctuated Equilibrium: a theory that speciation may occur during brief periods of rapid genetic change

• Gradualism: a theory that speciation may occur through a gradual change of adaptations

• Extinct: the state of a species that no longer exists– For a species to continue to exist, some

members must have traits that allow them to survive and pass their genes on to the next generation.

• Punctuated Equilibrium: a theory that speciation may occur during brief periods of rapid genetic change

• Gradualism: a theory that speciation may occur through a gradual change of adaptations

• Extinct: the state of a species that no longer exists– For a species to continue to exist, some

members must have traits that allow them to survive and pass their genes on to the next generation.