AP Bio Unit 7

evolution

any change in gene frequencies (gene pool) of a population over time

5 factors of evolution

1. genetic drift (small population)

2. sexual selection (non-random mating)

3. mutations

4. migration (gene flow)

5. natural selection

artificial selection

human driven evolutionary change in other species

natural selection is ….

the only way adaptive change occurs in a population

5 principles for natural selection

1. overproduction

2. variation

3. heritability

4. differential survival & reproduction

overproduction

species tend to produce more offspring than can survive to maturity

variation

there are phenotypic differences between members of a species

heritability

variations are often passed from parent to offspring

differential survival & reproduction

some phenotypes survive & reproduce better than others

• they will pass on their traits, increasing the frequency of beneficial traits in a population

individual fitness

how able an individual is to pass on their genes

• measured by reproductive success

ongoing selection

• biotic & abiotic factors can fluctuate in any environment

• selective pressures can change generation to generation affecting the rate and direction of evolution

directional selection

one extreme is selected for and the opposite is selected against

stabilizing selection

a moderate phenotype is selected for and both extremes are selected against

disruptive selection

• both extremes are selected for

• intermediate phenotype is selected against

• phenotype

  

  will diverge toward 2 extremes over time

sexual selection

adaptations can evolve purely for mating success

populations with _______ are generally more fit

greater levels of variation

high genetic diversity lets …

populations respond better to environmental changes

• more likely to contain individuals that can withstand new environmental pressures

species/populations with little genetic diversity are…

at risk of decline or extinction

genetic drift

evolution that occurs due to non-selective/random processes in small populations

bottleneck effect

type of genetic drift that occurs when population size is drastically reduced

• after the pop regrows the allele frequency has changed

• often results in loss of genetic diversity → pops are more vulnerable even after they have recovered

founder effect

type of genetic drift that occurs when a small group becomes isolated from the overall population

• allele frequencies in the new pop will not match those of the original pop

genetic drift & divergence

genetic drift can increase the liklihood of a small pop diverging into new species

gene flow

mvmt of alleles btwn pops

ways gene flow can occur

1. migration (btwn pops)

2. mating (btwn 2 members of diff pops)

continued gene flow btwn 2 pops….

prevents them from diverging into separate species because populations are not reproductively isolated

hardy-weinberg equilibrium

mathematical model that predicts allele frequencies in a non-evolving population

*no real population can actually be in hardy-weinberg equilibrium

conditions of hardy weinberg equilibrium

1. large population size

2. random mating

3. no new mutations

4. no migration

5. no natural selection

why hardy weinberg

it provides values we would expect in the absence of evolution

(null hypothesis)

gene pool

all alleles of a gene within a population

genotype frequency

frequency of AA, Aa, or aa

Allele frequency

frequency of A or a

p represents

frequency of A

q represents

frequency of a

p+q always equals…

1

• because all alleles in the gene pool are either A or a

p² =

frequency of AA

2pq =

frequency of Aa

q² =

frequency of aa

p² + 2pq + q² =

1

types of evidence for evolution

• geographical

• geological

• physical

• biochemical

• mathematical

geographical data

related species originated from common ancestral pop & spread via land bridges or continental mvmt

geological data

study of fossils & fossil age

relative dating

dating based off of position of fossils in layers of rocks

radioactive dating

measure age based off of half lives of radioactive isotopes

morphological data

comparing physical structures

• lets us draw conclusions abt evolutionary relationships btwn extant & extinct organisms

4 categories of morphological data

• embryology

• vestigial structures

• homologous structures

• analogous structures

vestigial structures

• reduced versions of structures that would have been functional in an ancestor

• provides evidence abt species ancestry

homologous structures

structures from different species that were inherited from a common ancestor

analogous structures

structures from different species that despite having a similar function do not show common ancestry

molecular data

• DNA & Protein sequencing

• strongest evidence for determining evolutionary relationships

  • avoids analogous structure prblm

  • many specific data points to use

molecular clock

molecular data can be used to make a “molecular clock” that will show when species diverged by determining the rate of mutation for a particular gene

mathematical data

use computer models to test hypotheses & predict most likely evolutionary models

common ancestry of all life

all living things share a common ancestor

common ancestry of life evidence

• universal genetic code

• shared conserved metabolic processes (glycolysis)

common ancestry eukarya evidence

• membrane bound organelles

• linear chromosomes

• genes contain introns

ongoing evolution

all species have & continue to evolve

phylogenetic trees & cladograms show…

evolutionary relationships among species

diff btwn phylogenetic trees & cladograms

phylogenetic trees show time while cladograms do not

hypothesis testing

phylogenetic trees can compare hypotheses from diff sources of evidence

phylogenetic tree outgroup

species least closely related to all other species on the tree

lineage

evolutionary history of a particular species

phylogenetic tree node

represents a common ancestor & subsequent speciation event where 2 lineages diverged

monophyletic group (aka clade)

includes all species descended from 1 common ancestor

polyphyletic group

does not include the most recent common ancestor of all species in the group

phylogenetic trees can show the…

gain/loss of traits

speciation

the formation of new species

• when subgroups of a species diverge into different species

species

group capable of interbreeding to produce viable, fertile offspring

prblms w/ species concept

• definition does not apply to asexually reproducing species

• is difficult to practically test

• doesn’t always hold true for all members of a species

for speciation to occur two populations must become..

• reproductively isolated

  • aka no more gene flow btwn pops

  • if maintained each pop evolves independently accumulating diff genetic changes

reproductive isolating mechanisms

anything that prevents gene flow btwn pops

pre-zygotic isolating mechanisms

prevent mating &/or fertilization

pre-zygotic habitat

live &/or mate in different locations

pre-zygotic temporal

mate at diff times

pre-zygotic behavioral

diff mating behaviors or phenotypes

pre-zygotic mechanical

reproductive anatomy incompatible

pre-zygotic gametic

sperm cannot fertilize eggs

post-zygotic isolating mechanisms

prevent viability or fertility of hybrid offspring

post-zygotic reduced hybrid viability

hybrids do not survive

post-zygotic reduced hybrid fertility

hybrids are sterile

allopatric speciation

occurs in pops that are geographically isolated

sympatric speciation

occurs in pops w/ geographic overlap

rates & patterns of speciation depend on..

environmental conditions

gradualism

when evolution occurs slowly over hundreds of thousands or millions of years

punctuated equilibrium

evolution occurs rapidly after a long period of stasis

divergent evolution

adaptation to new habitats results in new species becoming increasingly diff over time

adaptive radiation

many new habitats become available so rapid speciation & diversification occurs

convergent evolution

similar selective pressures result in similar phenotypic adaptations in diff species/pops

timeline of life on earth

• earth formed ~4.6 billion years ago(bya)

• environment was too hostile for life until 3.9 bya

• earliest fossil evidence for life 3.5 bya

RNA world hypothesis

RNA could have been the earliest genetic material

evidence for RNA world hypothesis

RNA can both encode info & act as a catalyst to self-replicate & assemble proteins

origin of life

life originated once

• all species on earth descended from single common ancestor