AP Biology- Unit 7 Natural Selection

EVERYTHING you need to know to understand unit 7 of AP Biology, Natural Selection!

Evolution

change in genetic makeup of pop over time

Natural Selection

organisms w/ adaptations best suited for that environment

-greater chance of survival + reproduction

-pass adaptations to subsequent generations

Competition

organisms v. organisms for limited resources

-space, food, mates, nutrients, light

Phenotype: how competitive an organism is

-Ex. Male Giraffes w/ longer necks are more favorable to female giraffes

This is competition for Mates

Genetic Variation

genetic differences in population

Increase w/ mutations+sexual reproduction

Increase population of organisms will survive under changing environmental conditions

Adaptations

Traits providing advantage in environment

-greater chance of reproduction

Selective Pressure

biotic+abiotic factors influencing survivability

-disease, climate, food availability

-changing env. → dif selective pressures

Ex. Dark colored moths fav after soot from industrial solution

after Clean Air Act → lighter phenotype favored

Fitness

Reproductive success over generations

ex. insecticide resistance in insects increase their fitness

Artificial Selection

Humans select desirable traits in other species

-selectively breed individuals w certain traits

-result in phenotypes that would not otherwise exist in nature

→ more OR less genetic diversity

Convergent Evolution

Similar environmental conditions select similar traits in different populations/species

Analogous Structures

Similar traits in related/unrelated species

ex. Aquatic env. → streamlined bodies in vertebrates (birds/fish)

Genetic Drift

Nonselective process

Random Change in allele frequency

-Natural disasters (fires, volcanos, eruptions)

Founder Effect

Random process reducing genetic variation in small pop

-Separation from a larger pop

-Migration and geological events isolate populations

Genetic makeup of founder pop dif from original

Bottleneck Effect

ex. of genetic drift

-size of pop. severely reduced

-result of environmental disaster, hunting

Gene Flow/Migration

movement of individuals between populations

• → exchange of alleles

• new genes into population → increased genetic variation

Hardy-Weinberg Equilibrium

Describes+Predicts allele frequencies in nonevolving population

5 Conditions of Hardy-Weinberg Equilibrium

• large population- no genetic drift (Bottleneck+Founder Effect)

• no migration

• no net mutation- no genes modified, deleted, duplicated

• random mating- no sexual selection

• no natural selection

Hardy-Weinberg Equation

Evidence for Evolution

Geographical- characteristics of habitat

Geological- environmental features of Earth over time (Fossils)

Physical- phenotypes

Biochemical- chemical composition (DNA+proteins)

Mathematical

Fossils

Dated by:

-age of rocks

-decay of isotopes

Provide info: Earth’s history

Morphological Homologies

Features shared by common ancestry

-variation in structure present in common ancestry

Vestigial Structures

-features serve little purpose for organism

ex. human tailbone

Biochemical evidence

-similar genetic code

-similar process of gene expression

Common Ancestry Evidence

-membrane-bound organelles

-endosymbiotic theory

-linear chromosomes in eukaryotes

Phylogenetic Tree

-evolutionary relationship among species

-shows changes over time through fossils/molecular evidence

-shows extinct lineages

-shows evolutionary timescale+degree of change through length of lines

Cladogram

evolutionary relationships among species

-clade indicates common ancestor

-lacks info

-DOES NOT show duration of lineage+amt. of evolutionary change

Out-group

Lineage least related to particular organisms

Speciation

-Populations reproductively isolated from each other

→ creation of new species

-diversity of life forms

Reproductive isolation

-no interbreeding

-cannot produce fertile offspring

-no gene flow between pop.

-prezygotic vs. postzygotic barriers

Prezygotic Barriers

Prevents production of fertilized egg

-habitat isolation

-temporal isolation: species breed at dif times

-behavioral isolation: mate preferences

-gamete isolation: sperm cannot fertilize egg of another species

Postzygotic Barriers

Prevents zygote from developing into a viable offspring

-hybrid inviability

-hybrid sterility

-hybrid breakdown: only first generation hybrids are viable are fertile

Allopatric Speciation

Evolution of new species due to population being geographically isolated over period of time

-no gene flow

-separation→ dif selective pressures

Sympatric Speciation

Reproductive isolation from surviving ancestral pop. →Evolution of new species

-no geographic barrier

-result of genetic mutations

-sexual selection

-habitat differentiation

→ high species biodiversity

Punctuated Equilibrium Model

-Evolution occurs after period of little/no change

changing ecological conditions→ evolution

Gradualism Model

Evolution over millions of years

-ecological conditions gradually change over long period of time

Divergent Evolution

Adaptation to new habitat→ phenotypic diversification

Adaptive Radiation

evolution of new species → empty ecological niches filled

Extinction

Human activity causes:

-habitat loss, climate change, habitat degradation, pollution, invasive species

Niche

Role of organism within env.

-producer, consumer, decomposer

when species goes extinct→ open niche for another species to occupy

→ adaptive radiation+ speciation

ex. after dinosaurs extinct→ mammals occupied niche

Genetically Diverse Populations

more resilient to environmental change

Environmental Pressures

-climate change

-catastrophic geological events

-habitat loss

-predation

Antibiotic Resistance

-population resilience

-resistance passed to offspring

-bacteria can give drug resistance to other bacteria (Conjugation)

Deleterious Traits

-reduce chance of survival

Adaptive Traits

Increase chance of survival

Selective pressures in env. determine if traits is advantageous/disadvantageousGe

Geological evd. of life on Earth

Earth formed: 4.6 bya

-Env. too hostile until 3.9 bya

-earliest fossil evidence for life 3.5 bya

Origin of Life on Earth

Primitive Earth: inorganic precursors for the synthesis of organic molecules

-Presence of free energy

-no O2 (atmos. oxygen)

-org. molecules could have come to earth by celestial event

Theory of formation of organic molecules

-shows organic molecules can be formed from inorganic molecules in the absence of life

-monomers building blocks of complex molecules

→ ability to replicate, store, + transfer info

RNA World Hypothesis

Proposes RNA could have been earliest genetic molecule

-stores info and carries out biological processes

unlike DNA/Protein which need each other