UNIT VIII EVOLUTION

• Big Campbell Ch 22-28, 31

• Baby CampbellCh 13-17

• HillisCh 15-18

I. EVOLUTION - WHAT IS IT?o “Descent with Modification”

o

“Change”

Population

November 24, 1859

II. Hardy-Weinberg Principle• Means used to determine if a population

is evolving• Predicts allele frequency in a non-

evolving population; that is, a population in equilibriumo States that allele frequencies in a

population will remain constant from generation to generation if five conditions are met

II. Hardy-Weinberg Principle, cont• Five Conditions for Hardy-Weinberg Equilibrium:

1)

2)

3)

4)

5)

If any of these conditions are not met, evolutionary change will occur!

II. Hardy-Weinberg Principle, cont• Hardy-Weinberg Equation

p = frequency of one allele (A) q = frequency of other allele (a) p + q =

• Therefore, p = q =

• Genotype Frequency AA = aa = Aa =

• To determine distribution of genotype frequencies in a population →

II. Hardy-Weinberg Principle, cont

Hardy-Weinberg Practice Problems1. If you know that you have 16% recessive fish (bb), . . .

• q 2 =• q = • Therefore, p =

To calculate the frequency of each genotype …• p2 =• 2pq =

What is the expected percentage of heterozygous fish?

II. Hardy-Weinberg Principle, cont• Hardy-Weinberg Practice Problems, cont

2. If in a population of 1,000, 90 show recessive phenotype (aa), use Hardy-Weinberg to determine frequency of allele combinations.

3. In people light eyes are recessive to dark. In a population of 100 people, 36 have light eyes. What percentage of the population would be …

• Homozygous recessive?

• Homozygous dominant?

• Heterozygous?

II. Hardy-Weinberg Principle, cont4. The ability to roll the tongue is a dominant trait. … 75% of the students at Kingwood High School have the ability to roll the tongue. Assuming the student population is 2526,

a) How many students would exhibit each of the possible genotypes?

b) How many students would exhibit each of the possible phenotypes?

III. A HISTORY OF EVOLUTIONARY THEORY

• Aristotle (384-322 BCE)o Scala Naturae

• Carolus Linnaeus (1707-1778)o Taxonomy

III. A HISTORY OF EVOLUTIONARY THEORY, cont

III. A HISTORY OF EVOLUTIONARY THEORY, cont• Charles Darwin (1809-1882)

III. A HISTORY OF EVOLUTIONARY THEORY, cont• Darwin, cont

o Observed many examples of adaptationsInherited characteristics

that enhance organisms’ survival and reproduction

o Based on principles of natural selectionPopulations of organisms

can change over the generations if individuals having certain heritable traits leave more offspring than others

Differential reproductive success

III. A HISTORY OF EVOLUTIONARY THEORY, cont

• Darwin’s Conclusions Based on his own observations and

the work of other scientists, Darwin realized … o Members of a population often

vary greatly in their traits.o Traits are inherited from parents to

offspring.o All species are capable of

producing more offspring that their environment can support, therefore …

III. A HISTORY OF EVOLUTIONARY THEORY, cont Darwin concluded …

o Individuals whose inherited traits give them a higher probability of surviving and reproducing in a given environment tend to leave more offspring than other individuals.

o This unequal ability of individuals to survive and reproduce will lead to the accumulation of favorable traits in the population over generations.

Descent with Modification

III. A HISTORY OF EVOLUTIONARY THEORY, cont• Artificial Selection

III. A HISTORY OF EVOLUTIONARY THEORY, cont

• Post-DarwinNeo-Darwinism/Modern Synthesis Theory

Epigenetics

IV. EVIDENCE FOR EVOLUTION

• Direct Observationo Antibiotic/Drug Resistance

IV. EVIDENCE FOR EVOLUTION, cont• Fossil Record

o Succession of forms over timeo Transitional Linkso Vertebrate descent

IV. EVIDENCE FOR EVOLUTION, cont

• Homologyo Homologous structures

o Vestigial organsSnakesCetaceansFlightless birds

IV. EVIDENCE FOR EVOLUTION, cont

o Convergent Evolution Independent evolution of similar features in different lineagesAnalogous structures

IV. EVIDENCE FOR EVOLUTION, cont

• Biogeographyo Geographical distribution of

specieso Continental Drift

Pangaeao Endemic specieso Islands are inhabited by

organisms most closely resembling nearest land mass

IV. EVIDENCE FOR EVOLUTION, cont

• Comparative Embryologyo Pharyngeal

Pouches Gill slits

o Tail

IV. EVIDENCE FOR EVOLUTION, cont

• Molecular Biologyo Similarities in DNA,

proteins, genes, and gene products

o Common genetic code

V. MICROEVOLUTION

• A change in the gene pool of a population over a succession of generations

• Five main causes:

V. MICROEVOLUTION, cont• Genetic Drift

o Changes in the gene pool due to chance. o More often seen in small population sizes. o Usually reduces genetic variability. o There are two situations that can drastically reduce population size:

Bottleneck EffectFounder Effect

V. MICROEVOLUTION, cont

• Bottleneck Effect Type of genetic drift resulting

from a reduction in population (natural disaster)

Surviving population is no longer genetically representative of the original population

• Founder Effect Due to colonization by a

limited number of individuals from a parent population

Gene pool is different than source population

V. MICROEVOLUTION, cont

• Gene FlowGenetic exchange due to the

migration of fertile individuals or gametes between populations – tends to reduce differences between populations

V. MICROEVOLUTION, cont

• MutationsA change in an

organism’s DNA (gametes; many generations); original source of genetic variation (raw material for natural selection)

V. MICROEVOLUTION, cont

• Nonrandom Mating Inbreeding Assortative mating

V. MICROEVOLUTION, cont

• Natural Selection

Only form of microevolution that adapts a population to its environment

VI. VARIATION IN POPULATIONS

• Genetic Variation is the “substrate” for evolution

• Maintained through … Polymorphism

Coexistence of 2 or more distinct forms of individuals (morphs) within the same population

Geographical Variation Differences in genetic

structure between populations (cline)

VI. VARIATION, cont Mutation and Recombination

Diploidy 2nd set of chromosomes hides

variation in the heterozygote

Balanced Polymorphism Heterozygote Advantage Frequency-Dependent Selection

o Survival & reproduction of any 1 morph declines if it becomes too common

o Parasite/host

VII. A CLOSER LOOK AT NATURAL SELECTION

• Natural Selection Not a random process → Dynamic processIncreases frequency of alleles that provide reproductive

advantageFitness

VII. CLOSER LOOK AT NATURAL SELECTION, cont

Natural selection is the only evolutionary mechanism for adaptive evolution

VII. CLOSER LOOK AT NATURAL SELECTION, cont

• Three ways in which natural selection alters variationDirectional

Disruptive

Stabilizing

VII. CLOSER LOOK AT NATURAL SELECTION, cont

• Sexual Selection Can result in sexual

dimorphism - secondary sex characteristic distinction

Intrasexual Selection

Intersexual Selection

VIII. MACROEVOLUTION

• Macroevolution Refers to the formation of new

taxonomic groups Due to an accumulation of

microevolutionary changes AKA Speciation

• “Species” Morphological Species Concept

Ecological Species Concept

Phylogenetic Species Concept

VIII. MACROEVOLUTION, cont

• Biological Species Concept Described by Ernst Mayr in

1942 A population or group of

populations whose members have the potential to interbreed and produce viable, fertile offspring; in other words, similar organisms that can make babies that can make babies

Can be difficult to apply to certain organisms . . .

VIII. MACROEVOLUTION, cont

• Reproductive Isolationo Prevent closely

related species from interbreeding when their ranges overlap.

o Divided into 2 typesPrezygoticPostzygotic

VIII. MACROEVOLUTION, cont

Prezygotic Reproductive Barriers

VIII. MACROEVOLUTION, cont

Postzygotic Reproductive Barriers

VIII. MACROEVOLUTION, cont• Speciation

o Fossil record shows evidence of bursts of many new species, followed by periods of little chanceKnown as punctuated equilibrium

o Other species appear to change more graduallyGradualism fits model of evolution proposed by Darwin

VIII. MACROEVOLUTION, cont• Modes of Speciation

Based on how gene flow is interrupted

Allopatric Populations segregated by a

geographical barrier; can result in adaptive radiation (island species)

Sympatric Reproductively isolated

subpopulation in the midst of its parent population (change in genome); polyploidy in plants; cichlid fishes

IX. HISTORY OF LIFE ON EARTH

IX. HISTORY OF LIFE ON EARTH, cont

• Formation of Organic Moleculeso Oparin/Haldane Hypothesis

Primitive Earth’s atmosphere was a reducing environment

No O2

Early oceans were an organic “soup”Lightning & UV radiation provided

energy for complex organic molecule formation

o Miller/Urey ExperimentTested Oparin/Haldane hypothesisSimulated atmosphere composed of

water, hydrogen, methane, ammoniaAll 20 amino acids, nitrogen bases,

ATP formedHypothesis was supported

IX. HISTORY OF LIFE ON EARTH, cont

IX. HISTORY OF LIFE ON EARTH, cont

IX. HISTORY OF LIFE ON EARTH, cont• Mass Extinctions

IX. HISTORY OF LIFE ON EARTH, cont• Adaptive Radiation

o Periods of evolutionary change, increased speciation

o Often due to increased ecological niches in communities

o Also seen in organisms with major evolutionary innovations

IX. HISTORY OF LIFE ON EARTH, cont

X. PHYLOGENY• Taxonomy

Linnaeus Binomial nomenclature Taxon (taxa)

X. PHYLOGENY, cont

• Evolutionary history of an organism

X. PHYLOGENY, cont• Phylogenetics

Tracing of evolutionary relationships

Illustrated with diagrams known as phylogenetic trees

X. PHYLOGENY, cont• Important to distinguish

between homologies and analogies Homologies are

likenesses attributed to common ancestry

Analogies are likenesses attributed to similar ecological roles and natural selection

• May also be done at a molecular level Known as molecular

systematics

X. PHYLOGENY, cont• Cladistics

Use of common ancestry as primary criterion for classificationSpecies are put into groups known as clades

Includes ancestral species + descendents Clades are sub-categorized as

Monophyletic – Includes ancestral group and all descendents

Paraphyletic – Includes ancestral group and some, but not all descendents

Polyphyletic – Includes taxa with multiple ancestorsParsimony – Also known as Occam’s Razor

X. PHYLOGENY, cont

X. PHYLOGENY, cont