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CHAPTER 17 Evolution of Populations

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Page 1: CHAPTER 17 Evolution of Populations. 17.1 Genes and Variation Genetics Joins Evolutionary Theory Heritable traits are controlled by genes Variation is

CHAPTER 17Evolution of Populations

Page 2: CHAPTER 17 Evolution of Populations. 17.1 Genes and Variation Genetics Joins Evolutionary Theory Heritable traits are controlled by genes Variation is

17.1 Genes and VariationGenetics Joins Evolutionary Theory

• Heritable traits are controlled by genes• Variation is the raw material for natural

selection

Page 3: CHAPTER 17 Evolution of Populations. 17.1 Genes and Variation Genetics Joins Evolutionary Theory Heritable traits are controlled by genes Variation is

Genotype and Phenotype in Evolution

• Alleles: specific forms of a gene• Genotype is the particular combination of

alleles• Natural selection acts directly on phenotype,

not genotype

Page 4: CHAPTER 17 Evolution of Populations. 17.1 Genes and Variation Genetics Joins Evolutionary Theory Heritable traits are controlled by genes Variation is

Populations and Gene Pools

• Members of a population interbreed, creating gene pools

• Gene pool consists of all genes• Allele frequency: number of times an allele

occurs in a gene pool

Page 5: CHAPTER 17 Evolution of Populations. 17.1 Genes and Variation Genetics Joins Evolutionary Theory Heritable traits are controlled by genes Variation is

Sources of Genetic Variation

• Genetics enable us to understand how heritable variation is published

• 3 sources of genetic variation: mutation, genetic recombination, lateral gene transfer

Page 6: CHAPTER 17 Evolution of Populations. 17.1 Genes and Variation Genetics Joins Evolutionary Theory Heritable traits are controlled by genes Variation is

Mutations

• Mutation: change in genetic material of a cell• Some mutations may be lethal• Mutations move from generation to

generation

Page 7: CHAPTER 17 Evolution of Populations. 17.1 Genes and Variation Genetics Joins Evolutionary Theory Heritable traits are controlled by genes Variation is

Genetic Recombination in Sexual Reproduction

• Crossing-over is another way genes are recombined

• Crossing-over increases the number of genotypes

• Mutations aren’t only source of heritable variation

Page 8: CHAPTER 17 Evolution of Populations. 17.1 Genes and Variation Genetics Joins Evolutionary Theory Heritable traits are controlled by genes Variation is

Lateral Gene Transfer

• Lateral gene transfer: passing genes from organism to organism that isn’t offspring

• Can increase genetic variation• Important to evolution of antibiotic resistance

in bacteria

Page 9: CHAPTER 17 Evolution of Populations. 17.1 Genes and Variation Genetics Joins Evolutionary Theory Heritable traits are controlled by genes Variation is

Single-Gene and Polygenic Traits

• Genes control phenotypes in different ways• Number of phenotypes on how many genes

control the trait

Page 10: CHAPTER 17 Evolution of Populations. 17.1 Genes and Variation Genetics Joins Evolutionary Theory Heritable traits are controlled by genes Variation is

Single-Gene Traits

• Trait controlled by only one gene• May have just two or three distinct

phenotypes• Controlled by dominant and recessive alleles

Page 11: CHAPTER 17 Evolution of Populations. 17.1 Genes and Variation Genetics Joins Evolutionary Theory Heritable traits are controlled by genes Variation is

Polygenic Traits

• Controlled by two or more genes• Often has two or more alleles• Creates a bell-shaped curve

Page 12: CHAPTER 17 Evolution of Populations. 17.1 Genes and Variation Genetics Joins Evolutionary Theory Heritable traits are controlled by genes Variation is

17.2 Evolution as Genetic Change in populationsHow Natural Selection Works

• Passes copies of its genes to its offspring• Genetically controlled traits

Page 13: CHAPTER 17 Evolution of Populations. 17.1 Genes and Variation Genetics Joins Evolutionary Theory Heritable traits are controlled by genes Variation is

Natural Selection on Single-Gene Traits

• Can lead to changes in allele frequencies• Lead to changes in phenotype frequencies• Mutation will help them survive and adapt

Page 14: CHAPTER 17 Evolution of Populations. 17.1 Genes and Variation Genetics Joins Evolutionary Theory Heritable traits are controlled by genes Variation is

Natural Selection on Polygenic Traits

• Affect relative fitness of phenotypes• Produce three types of selection• Directional selection, stabilizing selection,

disruptive selection

Page 15: CHAPTER 17 Evolution of Populations. 17.1 Genes and Variation Genetics Joins Evolutionary Theory Heritable traits are controlled by genes Variation is

Genetic Drift

• Random change in allele frequency• Natural selection isn’t only source of

evolutionary change

Page 16: CHAPTER 17 Evolution of Populations. 17.1 Genes and Variation Genetics Joins Evolutionary Theory Heritable traits are controlled by genes Variation is

Genetic Bottlenecks

• Change in allele frequency following dramatic reduction in population size

• Sharply reduce population’s genetic diversity• Different alleles than original population

Page 17: CHAPTER 17 Evolution of Populations. 17.1 Genes and Variation Genetics Joins Evolutionary Theory Heritable traits are controlled by genes Variation is

The Founder Effect

• Occur when few individuals colonize a new habitat

• New gene pool is different than the parent gene pool

• Change in allele frequency by migration of small subgroup

Page 18: CHAPTER 17 Evolution of Populations. 17.1 Genes and Variation Genetics Joins Evolutionary Theory Heritable traits are controlled by genes Variation is

Evolution Versus Genetic Equilibrium

• Allele frequencies don’t change• Population is not evolving

Page 19: CHAPTER 17 Evolution of Populations. 17.1 Genes and Variation Genetics Joins Evolutionary Theory Heritable traits are controlled by genes Variation is

Sexual Reproduction and Allele Frequency

• Gene shuffling during sexual reproduction produces gene combinations

• Meiosis and fertilization don’t change allele frequencies

• Populations would remain at genetic equilibrium

Page 20: CHAPTER 17 Evolution of Populations. 17.1 Genes and Variation Genetics Joins Evolutionary Theory Heritable traits are controlled by genes Variation is

The Hardy-Weinberg Principle

• Allele frequencies should remain constant unless factors cause it to change

• Makes predictions like Punnet squares• Predict frequencies of genotypes

Page 21: CHAPTER 17 Evolution of Populations. 17.1 Genes and Variation Genetics Joins Evolutionary Theory Heritable traits are controlled by genes Variation is

17.3 The process of speciationIsolating Mechanisms

• Speciation: formation of a new species• Gene pool can split

Page 22: CHAPTER 17 Evolution of Populations. 17.1 Genes and Variation Genetics Joins Evolutionary Theory Heritable traits are controlled by genes Variation is

Behavioral Isolation

• Differences in courtship rituals• Other behavioral differences can occur• Use different song to attract mates (east

meadowlark v. west meadowlark)

Page 23: CHAPTER 17 Evolution of Populations. 17.1 Genes and Variation Genetics Joins Evolutionary Theory Heritable traits are controlled by genes Variation is

Geographic Isolation

• Geographic barriers• Separate gene pools form• Barriers don’t always guarantee isolation

Page 24: CHAPTER 17 Evolution of Populations. 17.1 Genes and Variation Genetics Joins Evolutionary Theory Heritable traits are controlled by genes Variation is

Temporal Isolation

• Reproduce at different times• Orchids in the same rain forest are examples• Can’t pollinate with each other

Page 25: CHAPTER 17 Evolution of Populations. 17.1 Genes and Variation Genetics Joins Evolutionary Theory Heritable traits are controlled by genes Variation is

Speciation in Darwin’s Finches

• Occurred by founding of a new population • Galapagos Islands

Page 26: CHAPTER 17 Evolution of Populations. 17.1 Genes and Variation Genetics Joins Evolutionary Theory Heritable traits are controlled by genes Variation is

Founders Arrive

• Caused by founder effect• Allele frequencies differed from parent allele

frequencies• New species formed

Page 27: CHAPTER 17 Evolution of Populations. 17.1 Genes and Variation Genetics Joins Evolutionary Theory Heritable traits are controlled by genes Variation is

Geographic Isolation

• Combination of founder effect, geographic isolation, and natural selection

• Group of finches moved to another island• Another gene pool formed on that island

Page 28: CHAPTER 17 Evolution of Populations. 17.1 Genes and Variation Genetics Joins Evolutionary Theory Heritable traits are controlled by genes Variation is

Changes in Gene Pools

• Adapted to its local environments• New phenotypes occur as well• Not only birds, but plants too

Page 29: CHAPTER 17 Evolution of Populations. 17.1 Genes and Variation Genetics Joins Evolutionary Theory Heritable traits are controlled by genes Variation is

Behavioral Isolation

• Different evolution causes them not to be attracted to each other

• Could lead to reproductive isolation• Gene pools remain isolated

Page 30: CHAPTER 17 Evolution of Populations. 17.1 Genes and Variation Genetics Joins Evolutionary Theory Heritable traits are controlled by genes Variation is

Competition and Continued Evolution

• Compete for food• More specialized birds have less competition• Evolution of species increases over time

Page 31: CHAPTER 17 Evolution of Populations. 17.1 Genes and Variation Genetics Joins Evolutionary Theory Heritable traits are controlled by genes Variation is

17.4 Molecular EvolutionTiming Lineage Splits: Molecular Clocks

• Molecular clock uses mutation rates in DNA• Compare stretches of DNA to mark

evolutionary time

Page 32: CHAPTER 17 Evolution of Populations. 17.1 Genes and Variation Genetics Joins Evolutionary Theory Heritable traits are controlled by genes Variation is

Neutral Mutations as “Ticks”

• Molecular clock relies on a repeating process• Causes slight changes in sequence of DNA• Under powerful pressure of natural selection

Page 33: CHAPTER 17 Evolution of Populations. 17.1 Genes and Variation Genetics Joins Evolutionary Theory Heritable traits are controlled by genes Variation is

Calibrating the Clock

• Many different clocks• Different “ticks” at different rates• Some genes accumulate faster than others

Page 34: CHAPTER 17 Evolution of Populations. 17.1 Genes and Variation Genetics Joins Evolutionary Theory Heritable traits are controlled by genes Variation is

Gene Duplication

• Genes evolve through duplication• Modern genes descended from smaller

number of genes

Page 35: CHAPTER 17 Evolution of Populations. 17.1 Genes and Variation Genetics Joins Evolutionary Theory Heritable traits are controlled by genes Variation is

Copying Genes

• Carry several options of various genes• Can carry two copies of the same gene• An entire genome can be duplicated

Page 36: CHAPTER 17 Evolution of Populations. 17.1 Genes and Variation Genetics Joins Evolutionary Theory Heritable traits are controlled by genes Variation is

Duplicate Genes Evolve

• Undergo mutations to change their function• Evolve without effecting original gene function• Undergo copies

Page 37: CHAPTER 17 Evolution of Populations. 17.1 Genes and Variation Genetics Joins Evolutionary Theory Heritable traits are controlled by genes Variation is

Gene Families

• Produce hemoglobins• Focus on Hox genes• Group of related gene called gene family

Page 38: CHAPTER 17 Evolution of Populations. 17.1 Genes and Variation Genetics Joins Evolutionary Theory Heritable traits are controlled by genes Variation is

Developmental Genes and Body Plans

• “evo-devo”• Produce evolutionary changes we see in the

fossil record

Page 39: CHAPTER 17 Evolution of Populations. 17.1 Genes and Variation Genetics Joins Evolutionary Theory Heritable traits are controlled by genes Variation is

Hox Genes and Evolution

• Determine which parts of an embryo develop• Control size and shape• Can produce large changes in adults

Page 40: CHAPTER 17 Evolution of Populations. 17.1 Genes and Variation Genetics Joins Evolutionary Theory Heritable traits are controlled by genes Variation is

Timing is Everything

• Starts to grow at certain time• Grows for a specific time• Stops growing at a specific time