Unit 4: Evolution Grade 11 AP Bio

Evolution:

The change in genetic composition of a population during successive generations

Macroevolution

The evolution that occurs when a new species is developed

Microevolution

Change in frequency/percentage of alleles within a population

(not speciation, smaller degrees of change)

Aristotle (384-322) BC

Viewed the living world as fixed and unchanging

Arranged organisms in a ladder

(inferior -> superior organisms)

Theory of Uniformitarianism

James Hutton (1726-1797) + Charles Lyell (1797-1875)

States that the physical laws that now shape the earth have always done so

Catastrophism

Georges Cuvier (1769-1832)

One origin of life is wiped out by a catastrophic event

Organisms from other areas move in after the event

Line of Descent

Jean-Baptiste de Lamarck (1744-1829)

A progression between current species and fossil forms

Continues from original life to current life

Theory of Inheritance of Acquired Characteristics

Jean-Baptiste de Lamarck (1744-1829)

Giraffe's lengthened neck was passed onto its offspring

On the Origin of Species by Means of Natural Selection (Darwin)

1. Species were not created in their present form, but evolved from ancestral species

2. Proposed a mechanism for evolution - natural selection

Evolution by Natural Selection

1. Organisms produce more offspring than can survive. Therefore, organisms compete for limited resources.

2. Individuals of a population vary extensively, and much of this variation is heritable.

3. Individuals that are better suited to local conditions survive to produce more offspring.

4. Processes for change are gradual.

Descent with Modification

The changes in a population do not demonstrate progress, it is just change

Biogeography

The study of past and present geographical distribution of organisms

Geographically close environments are more likely to be populated by related species

Fossils

Fossils in younger rock are more similar to current species than those in deeper strata

Appear in chronological order in the rock - probable ancestors are found in older rocks

Homologous structures

Structures with similar structural elements and origin but may have a different function

Originates from a common ancestry

Analogous structures

Structures that do not have a common origin but perform similar functions

Vestigial structures

Structures that are reduced versions of what was a once function structure

Proved by fossil records that show past functional use of present day structure

Typically reduced in size and function in comparison to other members of a group

Embryological Similarities

Similar structures and similar developmental processes in embryos suggests common ancestry

Biochemical & Genetic Analysis

Species with similar DNA share a common ancestor

DNA evidence supports conclusions about relationships and common ancestry provided by other areas of evidence

Mutation

The original source of different alleles

The only source of new genetic variation

Creates variation within species

Selective advantages

A genetic advantage that improves an organism's chances of survival

Modern Synthesis

1. Acquired characters not inherited

2. Continuous variation explained by Mendelian genetics (Fisher)

3. Natural Selection (NS) can work with what is available in nature - nothing else is required

4. Speciation only requires natural selection not macromutation/acquired character

5. Species are not morphotypes - dynamic concept

Natural Selection

Individuals with favorable traits are more likely to leave more offspring which are better suited for reproduction

Requirements of Natural Selection

1. Phenotypic Variation

2. Heritability

3. Competition

4. Variations in survival + reproduction

Adaptation

Favored traits will spread through the population

Species will become adapted to their environment in response to environmental pressures

ex. Rock-pocket mice

Types of natural selection

Directional selection

Stabilizing selection

Disruptive selection

Directional selection

A specific extreme of a gene is favoured

Stabilizing selection

Favours intermediate phenotypes and acts against extreme variants

Disruptive selection

Both extremes of a gene are favoured

Often leads to new species being formed

Sex-linked usually does not lead to speciation

Artificial Selection (Selective Breeding)

The selective breeding of domesticated plants and animals to encourage the occurrence of desirable traits

Advantages of Selective Breeding

Allows us to choose desirable traits

Disease resistance

Endurance

Strength

Tameness

Disadvantages of Selective Breeding

Other traits become negatively affected

Decreases genetic diversity

Monocultures

A large area with one type of plant with little genetic diversity

Usually uses artificial selection

Gene Pool

All of the alleles of all of the individuals in a genetic population

Genetic Population

An array of alleles temporarily embodied in individuals but combines through sexual reproduction and conjugation

Allelic frequency

Represents the incidence of a gene variant in a population

Divide # of times the allele is observed by copies of all alleles in the population

Genotypic Frequency

Represents the proportion of a specific genotype in a population

# of individuals in the population with the trait divided by total # of individuals

5 Causes of Microevolution

1. Mutation

2. Gene flow (migration)

3. Non-random mating

4. Genetic drift

5. Natural selection

Mutation (Microevolution)

The source of genetic variation

Causes more genetic diversity and selective advantages for some individuals

Gene flow (Microevolution)

The net movement of alleles from one population to another

A result of the migration of individuals

Can both separate and unite populations

Non-Random Mating (Microevolution)

Mating among individuals on the basis of a particular phenotype/due to inbreeding

3 Types of Non-Random Mating

Assortative Mating

Disassortative Mating

Inbreeding

Assortative Mating

Preference for similar genotypes or phenotypes

Usually leads to directional/stabilizing

Disassortative Mating

Preference for different genotypes or phenotypes

Most likely leads to disruptive(when trait is not sex-linked)

Inbreeding

Occurs when closely related individuals breed

Can occur naturally or by human-led breeding program

Genetic Drift (Microevolution)

The change in frequencies of alleles due to random events in a small breeding population

Smaller populations have less genetic variation, more genetic drift

2 Types of Genetic Drift

Founder Effect

Bottleneck Effect

Founder Effect

A new population is begun by a few migrating individuals

New pop. gene pool only has alleles from founders - gene pool is reduced

Causes extreme genetic drift

Bottleneck Effect

An existing population is quickly reduced in size by environment

Survivors have a fraction of the alleles present

Extreme loss of genetic diversity, high genetic drift

3 Types of Natural Selection (Microevolution)

1. Sexual selection

- Intersexual selection

- Intrasexual selection

2. Altruism

3. Kin Selection

Intersexual Selection

Member of one sex chooses other to mate with

Usually female choice

Explains flamboyant appearance in birds

Intrasexual selection

Members of one biological sex compete with members of the same sex for access to members of the opposite sex

Explains Male vs. Male Competition

Altruism

Individual behaviour benefits a social group at the expense of the individual

Helping another organism at a detriment to yourself

Animal does not have to be related/family

Kin Selection

Version of altruism

Helpful behaviour for family/kin

Ensures some part of the family's genes are passed on

Sibling helps sibling = children carry similar genes, ensures survival

Bateman's Principle

Female reproductive success is limited by access to resources

Male reproductive success is limited by access to females

Sexually Monomorphic

Males & females look similar

Sexually Dimorphic

Male & females look different

Good Genes Hypothesis

Secondary sexual characteristics signal increased fitness

Post-copulatory Selection

Sperm competition - competes for fertilization

Females can also choose (sperm storage, etc)

Sexy Sons Hypothesis

Having a sexy partner = having a sexy son

Fisherian Runaway Selection

Cost of trait vs cost of benefit(reproductive success)

Balance is found in between both costs

Hardy-Weinberg Equilibrium

When a population is not evolving and allele frequencies stay the same

5 Requirements for H-W Equilibrium

1. No Mutation

2. Random Mating

3. No natural selection

4. No Migration

5. Large population

H-W Equation

p^2 + 2pq + q^2 = 1

p+q=1

Species

The most basic category of biological classification

No universally applicable concept

Speciation

Occurs when a group within a species separates from other members of its species and develops its own unique characteristics

Caused by:

- Genetic distinctiveness

- Reproductive isolation

Reproductive Isolation

Allows species to evolve independently of other species

Biological Species Concept

Species recognize each other as mates

Offspring is viable and fertile

Organisms are reproductively isolated from other populations

Anagenesis

Evolutionary change within lineages over time

Cladogenesis

Splitting of lineages over time

2 Categories of Reproductive Isolation

Pre-Zygotic

Post-Zygotic

2 Categories of Pre-Zygotic Isolation

Prevention of Mating

- Behavioural Isolation

- Temporal Isolation

- Ecological/Habitat Isolation

Prevention of Fertilization

- Mechanical Isolation

- Gametic Isolation

Behavioural Isolation

Differences in mating behavior leads to reproductive isolation

Organisms do not recognize each other's mating rituals

Temporal Isolation

Differences in the timing of mating prevents different species from interbreeding

Ecological/Habitat Isolation

Species occupy different habitats - do not meet

Mechanical Isolation

Anatomical differences make mating physically impossible

ex. genitalia, body size

Occurs often in plants and insects

Floral Isolation (Type of Mechanical)

Flower structures & pollination methods are different

Gametic Isolation

Gametes of different species cannot fuse

Organisms who use random mating must use gametic isolation

Hybrids

The offspring of parents from two genetically distinct populations

Postzygotic barriers reduce viability or fertility

Reproduction of fertile hybrids can lead to formation of a new species

Types of Post-zygotic Isolation

Zygotic Mortality

Hybrid Inviability

Hybrid Infertility/Sterility

+

Hybrid Breakdown

Zygotic Mortality

Zygote is not viable

Fused zygote immediately stops developing - does not reach pregnancy

Hybrid Inviability

Hybrid zygotes fails to develop into an adult hybrid

Dies before reaching maturity

Mammal species - dies before birth

Hybrid Infertility

Hybrids live to adulthood but cannot produce viable gametes

Hybrid Breakdown

Fertile hybrid is formed, reaches adulthood

Offspring has reduced fitness

Modes of Speciation

Allopatric Speciation

Peripatric Speciation

Parapatric Speciation

Sympatric Speciation

Allopatric Speciation

Population is split into 2+ isolated groups by a geographical barrier

Reproductive isolation evolves in the different populations

Genetic divergence through: natural selection, mutation, genetic drift

Most common mode of speciation (believed to be)

Peripatric Speciation (Founder Effect)

Small population is isolated from parent population

Genetic divergence through: natural selection, genetic drift

Parapatric Speciation

Continuous population

Modest gene exchange occurs

Genetic divergence through: natural w selection

Continuous population

Neighboring populations share small zones of contact

Sympatric Speciation

1 interbreeding population - reproductive isolation occurs within it

Genetic divergence through: diversifying selection, polyploidy

Polyploidy

3+ sets of chromosomes

Error in cell division -> extra set(s) of chromosomes

Organism becomes reproductively & genetically isolated from population

Rare in animals, common in plants

Strawberry genome (polyploidy)

Commercial strawberry - octoploid

2n=8

8 x 7 chromosome sets = 56 total

Allopolyploids

Allopolyploidy

Genome comes from different ancestral diploid sub-genomes

Comes from gametic non-reduction (daughter cell keeps all parent cell chromosomes) + cross pollination

Rate of Speciation

Full process takes long periods of time

Varies widely

Influenced by a variety of factors

i.e. size & degree of geographic isolation

Mass extinction

The extinction of a large number of species within a relatively short period of geological time

Occurs due to catastrophic events or rapid widespread environmental change

Results in a burst of evolution of new species filling empty niches

Adaptive Radiation (divergent evolution)

The evolution of an animal or plant group into a wide variety of types adapted to specialized modes of life

Convergent evolution

Opposite of divergent evolution/adaptive evolution

Unrelated organisms independently evolve similarities when adapting to similar environments/niches

Analogous structures are produced

Coevolution

When two species evolve in response to changes in each other

Closely connected by ecological interactions (symbiotic relationships)

Each party exerts selective pressures on the other

Gradualism

The evolution of new species by gradual accumulation of small genetic changes over long periods of time

Punctuated Equilibrium

"Equilibrium" is "punctuated" by episodes of very fast development of new forms

Involves many different lines of descent

Opposite of gradualism

Rare & rapid event of speciation