unit 7 biology

12th grade ap biology

charles darwin

- english naturalist

- researched at galapagos islands

- interested in biogeography (geographic distribution of species)

- hypothesis: organisms left south america and colonized the galapagos islands where they then diversified and gave rise to new species

descent with modification/evolution

- change in the genetic makeup of a population over time

- population evolve, not individuals

heritable traits

change from generation to generation

natural selection

- a process in which individuals that have certain traits tend to survive and reproduce at higher rates than other individuals because of those traits

- acts on phenotypic variations in populations. some phenotypes will increase or decrease an organism's fitness

- nature "selects" traits that are better suited for survival and reproduction

fitness

- ability to survive and reproduce

- measured by reproductive success

selective pressures

happens to populations when environments change

theory of natural selection

- based on darwin's observations

1. traits are heritable

2. more offspring are produced than can survive

traits are heritable

- characteristics can be passed from parent to offspring

- adaptations

adaptations

inherited characteristics of organisms that enhance their survival and reproduction

more offsprings produced than can survive

- leads to competition for limited resources, resulting in differential survival

- traits that lead to survival (favorable traits) will accumulate in the population

artificial selection

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

- humans select traits that are desirable

population

- a group of individuals of the same species that live in the same area and interbred to produce fertile offspring

- allele frequency will change over time

gene pool

- a population's genetic makeup

- consists of all copies of every type of allele

- if there is only one allele present for a particular locus in the population, it is fixed

fixed alleles

leads to less genetic diversity

microevolution

- small scale genetic changes in a population/change in allele frequencies within a single species or population

- driver by random occurrences: mutations, genetic drift, migration/gene flow, natural selection

mutations

- can result in genetic variation

- can form new alleles

- natural selection can act on varied phenotypes

- rates tend to be slow in plants and animals; fast in prokaryotes due to a faster generation time

- most all in neutral to harmful range

- not all lead to evolution

genetic drift

- chance events that cause a change in allele frequency from one generation to the next

- most significant to small populations

- can lead to a loss of genetic variation

- can cause harmful alleles to become fixed

- does not produce adaptation

- types: bottleneck and founder effect

bottleneck effect

- when a large population is drastically reduced by a non-selective disaster

- some alleles may become overrepresented, underrepresented, or absent

- ex: natural disasters, hunting, habitat loss

founder effect

- when a few individuals become isolated from a large population and establish a new small population with a gene pool that differs from the large population

- lose genetic diversity

- ex: amish ppl

gene flow

- the transfer of alleles into or out of a population due to fertile individuals or gametes

- alleles can be transferred between populations

- ex: pollen being blown

reproductive success

measured by relative fitness

relative fitness

the number of surviving offspring that an individual produces compared to the number left by others in the population

measuring effects of natural selection

- measured by examining the changes in the mean of phenotypes

1. directional selection

2. stabilizing selection

3. disruptive selection

directional selection

- selection towards one extreme phenotype

- ex: black or white shells

stabilizing selection

- selection towards the mean and against the extreme phenotypes

- ex: gray shells

disruptive selection

- selection against the mean, both phenotypic extremes have the highest relative fitness

- ex: against gray shells, favor black and white shells

sexual selection

- a type of natural selection that explains why many species have unique/showy traits

- can produce traits that are harmful to survival

- ex: peacock feathers

evolution evidence

- fossil record

- comparative morphology

- biogeography

fossils

- remains or traces of past organisms

- can be dated by examining the rate of carbon 14 decay and the age of rocks where it was found

fossil record

- gives a visual of evolutionary change over time

- gives geographical data for the organisms found

comparative morphology

- analysis of the structures of living and extinct organisms

- includes homology, vestigial structures, convergent evolution, analogous structures

homology

characteristics in related species that have similarities even if the functions differ

embryonic homology

many species have similar embryonic development

vestigial structures

- structures that are conserved even though they no longer have a use

- ex: appendix, wisdom teeth

molecular homology

many species share similar DNA and amino acid sequences

homologous structures

- characteristics that are similar in two species because they share a common ancestor even though functions differently

- ex: arm bone

convergent evolution

- similar adaptations that have evolved in distantly related organisms due to similar environments

- ex: analogous traits

analogous structures

- structures that are similar but have separate evolutionary origins

- ex: wings in birds, bats, and bees

structural evidence

- indicates common ancestry of all eukaryotes

- cellular examples: membrane-bound organelles, linear chromosomes, introns in genes

biogeography

- the distribution of animals and plants geographically

- ex: species on oceanic islands resemble mainland species

- ex: species on same continent are similar and distinct from species on other continents

hardy weinberg equilibrium

- used to assess whether natural selection or other factors are causing evolution at a particular locus

- determines what the genetic makeup of the population would be if it were not evolving

- no differences -> population not evolving

- differences -> population may be evolving

hardy weinberg principle

frequencies of alleles and genotypes in a population will remain constant from generation to generation, provided that only mendelian segregation and recombination of alleles are at work

hardy weinberg conditions

- no mutations

- random mating

- no natural selection

- extremely large population size

- no gene flow

- if any are met, then microevolution occurs

alleles

p + q = 1

genotypes

p² + 2pq + q² = 1

dominant allele

p

recessive allele

q

homozygous dominant

p²

heterozygous

2pq

homozygous recessive

q²

systematics

classification of organisms and determining their evolutionary relationships

taxonomy

naming and classifying species

phylogenetics

- hypothesis of evolutionary history

- use phylogenetic trees to show evolution

how scientists determine evolutionary relationships

- fossil records

- DNA (most exact)

- proteins

- homologous structures

phylogenetic trees

- diagrams that represent the evolutionary history of a group of organisms

- shows the amount of change over time measured by fossils

cladograms

similar to phylogenetic trees

lineage

each line on a cladogram

node

- each branching point on a cladogram

- represent common ancestor

clades

- nodes and all branches from it

- species have shared derived features

root

common ancestor of all the species

sister taxa

- two clades that emerge from the same node

- can swap places

basal taxon

- a lineage that evolved from the root and remains unbranched

- out group: least related to the rest

synapomorphy

a derived character shared by clade members

derived characteristics

similarity inherited from the most recent common ancestor of an entire group

ancestral characteristic

similarity that arose prior to the common ancestor

monophyletic group

includes the most recent common ancestor of the group and all of its descendants (clade)

paraphyletic group

includes the most recent common ancestor of the group but not all its descendants

polyphyletic group

does not include the most recent common ancestor of all members of the group

parsimony

if there are conflicts among characters, use the hypothesis that requires the fewest assumptions (DNA changes)

species

a group able to interbreed and produce viable, fertile offspring

speciation

- formation of new species

- results in diversity of life forms

- occurs due to reproductive isolation

allopatric speciation

- physical barrier divides population or a small population is separated from main population

- populations are geographically isolated: prevents gene flow, often caused by natural disasters

sympatric speciation

- a new species evolves while still inhabiting the same geographic region as the ancestral species

- usually due to the exploitation of a new niche

reproductive isolation

prezygotic barriers and postzygotic barriers maintain isolation and prevent gene flow between the populations

prezygotic barriers

- before fertilization

- prevent mating or hinder fertilization

- types: habitat isolation, temporal isolation, behavioral isolation, mechanical isolation, gametic isolation

habitat isolation

species live in different areas or they occupy different habitats within the same area

temporal isolations

species breed at different times of the day, year, or season

behavioral isolation

unique behavioral patterns and rituals separate species

mechanical isolation

the reproductive anatomy of one species does not fit with the anatomy of another species

gametic isolation

proteins on the surface of gametes do not allow for the egg and sperm to fuse

postzygotic barriers

- after fertilization

- prevent a hybrid zygote from developing into a viable, fertile adult

- types: reduced hybrid viability, reduced hybrid fertility, hybrid breakdown

reduced hybrid viability

- the genes of different parent species may interact in ways that impair the hybrid's development or survival

- ex: domestic sheep can fertilize domestic goats, but the hybrid embryo dies early on

reduced hybrid fertility

- a hybrid can develop into a healthy adult, but it is sterile

- usually results due to differences in number of chromosomes between parents

- ex: male donkey and female horse can mate to produce a mule, but mules are sterile

hybrid breakdown

- the hybrid of the first generation may be fertile but when they mate with a parent species or one another, their offspring will be sterile

- ex: farmers crossing different types of cotton plants but after the first generation the plants do not produce viable seeds

macroevolution

large evolutionary patterns (adaptive radiation, mass extinction)

stasis

no change over long periods of time

punctuated equilibrium

when evolution occurs rapidly after a long period of stasis

gradualism

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

divergent evolution

- groups with the same common ancestor evolve and accumulate differences resulting in the formation of a new species

- caused by adaptive radiation

adaptive radiation

if a new habitat or niche becomes available, species can diversify rapidly

extinction

- the termination of a species

- 5 mass extinctions in history

- human activity has affected rates

- quickens during ecological stress

- extinction of a species opens up a niche that can be exploited by a different species

origins of life

- earth formed approximately 4.6 billion years ago

- early earth was not suitable for life until 3.9 billion years ago

- earliest fossil evidence is 3.5 billion years ago (cyanobacteria)

how organic molecules formed

- inorganic molecules could have synthesized them due to free energy and abundant oxygen

- could have been transported to earth via meteorites or other celestial events

stanley miller and harold urey

- found organic compounds and amino acids formed from lightning

- hypothesized that the organic molecules that formed served as the building blocks for macromolecules

RNA world hypothesis

- proposes that RNA could have been the earliest genetic material

- helps to explain the pre-cellular stage of life

endosymbiont theory

- chloroplast and mitochondria evolved from prokaryotes

- evolutionary evidence: circular DNA, ribosomes, double membrane