Warm Up Describe natural selection and how this leads to evolution.

What is a mechanism?

Mechanisms of Evolution Natural Selection Population Genetics Genetic Drift Gene Flow Nonrandom mating Mutation

Individuals in a population show variations. Evolution Natural Selection Population Genetics Individuals in a population show variations. Variations can be inherited. Organisms have more offspring than can survive on available resources. Variations that increase reproductive success will have a greater chance of being passed on.

Acts on an organisms phenotype and change allele frequencies. Natural Selection Acts to select the individuals that are best adapted for survival and reproduction. Acts on an organisms phenotype and change allele frequencies.

Allele Frequencies

Types of Natural Selection Stabilizing Selection Directional Selection Disruptive Selection Sexual Selection

Types of Natural Selection Evolution Types of Natural Selection Stabilizing selection average phenotype has the highest fitness eliminates extreme phenotypes

Types of Natural Selection Evolution Types of Natural Selection Directional selection One Extreme phenotype has the highest fitness Selection in one direction makes an organism more fit.

Types of Natural Selection Evolution Types of Natural Selection Disruptive selection Splits population into two groups. Extreme phenotypes have higher fitness than the average phenotype

Types of Natural Selection Evolution Types of Natural Selection Sexual selection In populations where males and females differ significantly in appearance.

Sexual Selection Qualities of sexual attractiveness appear to be the opposite of qualities that might enhance survival.

Stabilizing Selection Evolution Natural Selection Stabilizing Selection Directional Selection Disruptive Selection

Greater in smaller populations Greater Chance of losing an allele Evolution Genetic Drift A change in the allele frequencies in a population that is due to chance Greater in smaller populations Greater Chance of losing an allele

Small Population (Genetic Drift) Evolution Genetic Drift Small Population (Genetic Drift)

Genetic Drift Founder Effect Bottleneck

Genetic Drift Founder Effect Evolution Genetic Drift Founder Effect small part of a population settles in a location separated from the rest of the population Alleles that were uncommon in the original population might be common in the new population.

population declines to a very low number then rebounds Genetic Drift Evolution Bottleneck Occurs when: population declines to a very low number then rebounds

Genetic Drift Bottleneck Population Decreases The Survivors Repopulate Evolution Bottleneck Population Decreases The Survivors Repopulate What is Different? Why could less diversity be bad? Less Diversity

Increases genetic variation within a population Evolution Gene Flow Increases genetic variation within a population reduces differences between populations

Nonrandom Mating Promotes inbreeding Evolution Nonrandom Mating Promotes inbreeding could lead to a change in allele proportions favoring individuals that are homozygous for particular traits

Chapter 15 Evolution 15.3 Shaping Evolutionary Theory Gene Flow Increases genetic variation within a population and reduces differences between populations Nonrandom Mating Promotes inbreeding and could lead to a change in allelic proportions favoring individuals that are homozygous for particular traits

Mutation Random change in genetic information Cause changes in allele frequencies Some advantageous

Speciation Species diverge Can occur due to isolation Become two separate species that cannot reproduce Allopatric speciation Sympatric speciation

Isolation Reproductive Isolation gene Flow is prevented between two populations of the same species. different mating seasons

Isolation Geographic Isolation A population that becomes divided (isolated) by a physical barrier Each groups evolves differently

Chapter 15 Evolution Abert squirrel Kaibab squirrel

Allopatric Speciation Sympatric Speciation Evolution Allopatric Speciation Sympatric Speciation A species evolves into a new species without a physical barrier. A physical barrier divides one population into two or more populations.

Which is not a principle of Darwin’s theory about Chapter 15 Evolution Chapter Diagnostic Questions Which is not a principle of Darwin’s theory about the origin of species? Individuals show variations. Variations can be inherited. Organisms have more offspring than available resources will support. Offspring always inherit the best traits.

Which description is evidence that a speciation has taken place? Chapter 15 Evolution 15.3 Formative Questions Which description is evidence that a speciation has taken place?

A physical barrier has caused two groups from a Chapter 15 Evolution 15.3 Formative Questions A physical barrier has caused two groups from a population to adapt to different environments. Some members can no longer produce fertile offspring with members of the original population. A small group has developed mating behaviors that are different than those of the rest of the population. Some members from a population have developed physical characteristics that are different than the original population.

Within a population of squirrels, those that Chapter 15 Evolution Standardized Test Practice Within a population of squirrels, those that live higher in the mountains where it is cooler have long fur. Squirrels that live in the foothills where it is warmer have short fur. The original population is believed to have had intermediate fur length. Which graph represents this type of natural selection?

Standardized Test Practice Chapter 15 Evolution Standardized Test Practice

Contrast the four types of natural selection.