AP Bio Unit 7

Charles Darwin

english naturalist

mist notable research done at Galapagos islands

Charles Darwin’s research

Darwin was interested in biogeography

• the geographic distribution of species

Darwin’s hypothesis

Organisms left South America and colonized the Galapagos Islands were they then diversified and gave rise to new species

• Darwin was specifically looking at finches

During his studies…

Darwin proposed the idea of descent with modification, which is now our modern definition of evolution

evolution

change in the genetic makeup of a population over time; descent with modification

• heritable traits change from generation to generation

• time is important component of evolution

to explain the pattern of descent with modifcation (evolution) he observed, Darwin proposed the idea of natural selection

• mechanism of action for evolution

natural selection

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

• natural selection acts on phenotypic variations in populations

• some phenotypes increase or decrease an organism’s fitness (ability to survive and reproduce)

  • measured by reproductive success

• environents can change, causing selective pressures to populations

the theory of natural selection is based on two main observations that Darwin made

1. traits are heritable

2. more offspring are produced than can survive

traits are heritable

characteristics can be passed from parent to offspring

• adaptations: inherited characteristics of organisms that enhance their survival and reproduction

more offspring are produced than can survive

this leads to competition for limitied resources, which results in differential survival

• traits that lead to survival (favorable traits) will accumalte in the population

  • populations evovlve, not individuals

artificial selection

at the time, Darwin was worried about other scientists supporting his work. So he compelled them by comparing natural selection to artifical selection

artificial selection

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

natural vs artificial selection

nature selects “traits” that are better suited for survival and reproduction

art:

humans select traits that are desierable

domestication of plants and animals

note: both can lead to evolutionary change in the organism, but natural selection occurs in nature without the influence of humans

population

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

gene pool

a population’s genetic make-up

• 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

many fixed alleles = less genetic diversity

a population’s allele frequences will change over time

remember that populations evolve not individuals

microevolution

small scale genetic changes in a populaiton

evolution is driven by…

random occurences

• mutations

• genetic drift

• migration/gene flow

• natural selection

mutations

mutations can result in genetic variation

can form new alleles

natural selection can act on varied phenotypes

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

mutations can be harmful, neutral, or beneficial. Most mutations are in the neutral to harmful range. Not all mutations 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 harumful alleles to become fixed

• does not produce adaptations

two types

1. bottleneck effect

2. founder effect

bottleneck effect

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

flood famine, fires, hurricanes, hunting, etc

some alleles may become overrepresented, underrepresented, or absent

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

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 to new location

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 adaptations

two types of genetic drift

bottleneck effect

founder effect

bottleneck effect

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

• floods, famine, fires, hurricanes, hunting, etc

• some alleles may become overrepresented, underrepresented, or absent

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

gene flow

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

alleles can be transferred between populations

• example: pollen being blown to new location

natural selection

reproductive success is measured by relative fitness

• the number of surviving offspring that an individual produces compared to the numbered produced by others in a population

effects of natural selection can be measured by examining the changes in the mean of phenotypes

• there are three modes of natural selection: 1) directional selection, 2) stabilizing selection, 3) disruptive selection

directional selection

selection towards one extreme phenotype

stabilizing selection

selection towards the mean and against the extreme phenotypes

disruptive selection

selection against the mean

both phenotypic extremes have highest relative fitness

sexual selection

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

males often have useless structures (ie colorful male peacock feathers) simply because females choose that trait

• can produce traits that are harmful to survival

• example: colorful feathers in male peacocks make them easier to spot by predators

hardy weinberg equilibrium

a model used to assess whether natural seleciton or other factors causing evolution at a particular locus

determines what the genetic make up of then population is not evolving

this is then compared to actual data

• if there are no differences then the population is not evolving

• if there are differences then the population may be evolving

five conditions must be met to be in Hardy weinberg equilibirum

no mutations

random mating

no natural selection'

extremeley large pop. size

no gene flow

if any of these conditions are not met, then microevolution occurs

allele frequency formula

p+q=1

p = frequency of the dominant allele in a population

q = frequency of the recessive allele in the population

genotypic frequency formula

p²+2pq+q²=1

p²=frequncy of the homozygous dominant individuals

2pq=frequency of heterzygous individuals

q²=frequency of homozygous recessive individuals

HW equilibrium

which formula you start with depends on the information you are given

if a problem gives “allele frequencies” it is referring to p and q. If it gives information about individual organisms or populations then it is referring to p²,2pq,q²

most times you will use both formulas to complete the problem

usually you are given q and then you will need to find p, but now you will also see problems where that is not the case

tips for solving problems

1. always write down both equations

2. identify the information given. Is it for alleles or genotype?

3. regardless of what the problem asks, solve for p and q first, bc that will allow you to answer any question

4. use calc

5. double check

evidence of evolution

overwhelming evidence supports the theory of evolution

primary sourcs of evidence are

• the fossil record

• comparative morphology

• biogeography

fossil record

fossils: remains or traces of past organisms

fossil record: gives a visual of evolutionary change over time

fossils can be dated by examining the rate of carbon 14 decay and the age of rocks where the fossils are found

• gives geopraphical data for the organisms found

comparative morphology

the analysis of structures of living and extinct organisms

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: tailbone and appendix in humans

molecular homology

many species share similar DNA and amino acid sequences

homologous structures

characteristics that are similar in two species becuase they share a common ancestor

potentiallt different functions

ex: arm bones of many species

convergent evolution

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

analogous structures

structures that are similar buth have separate evolutionary origins

example: wings in birds vs bats vs bees

each species have wings, but the wings did not originate from a common ancestor

structural evidence indicates common ancestry or all eukaryotes

• many fundamental and cellular deatures and processes are conserved across organisms

• ex: membrane bound organelles, linear chromosomes, introns in genes

biogeography

the distribution of animals and plants geographically

example: species on oceanic islands resemble: mainland species

example: species on the same continent are similar and distinct from species on other countinents

systematics

classification of organiusms and determining their evolutionary relationships

taxonomy

naming and classifying species

phylogenetics

hypothesis of evolutionary history

use phylogenetic trees to show evolution

to determine evolutionary relationships, scientists use:

fossil records

DNA

proteins

homologous structures

phylogenetic trees

diagrams that represent the evolutionary history of a group of organisms

similar to cladograms, except trees show the amount of change over time measured by fossils

cladograms

each line represents a lineage

each branching point is a node

nodes represent common ancestors

• nodes and all branches from it are called clades

• species in a clade have shared derived features

the root is the common ancestor of all the species

sister taxa

two clades that emerge from the same node

basal taxon

a lineage that evolved from the root and remains unbranched

synapomorphogy

a derived characteristic shared by clade members

derived characteristic

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

ancestral characteristic

similarity that arose prior to the common ancestor

outgroup

included in many cladograms and trees

a lineage that is least closely related to the rest of the organisms

monophyletic group

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

paraphyletic group

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

polyphyletic group

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

parsimony

if there are conflicts among characters, use the principle of parsimony

• 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

geography has an impact on speciation'

two modes of speciation: allopatric speciation and sympatric speciation

allopatric speciation

physcial barrier divides population or a small population is seperated from the main population

populations are geogrpahically isolated

• prevents gene flow

• often caused by natural disasters

sympatric speciation

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

• usually due to the exploitation of a new niche

speciation occurs due to

reproductive isolation

two types of reproductive isolation

prezygotic barriers

postzygotic barriers

both types maintain isolation and prevent gene flow between the populations

prezygotic barriers

prevent mating or hinder fertilization

5 types:

1. habitat isolation

2. temporal isolation

3. behavioral isolation

4. mechanicial isolation

5. gametic isolation

habitat isolation

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

ex: in western North America the mountain bluebird lived at high elevation while the eastern bluebird lives at low elevation

temporal isolation

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

example: the western spotted skunk mates in late summer, while the eastern spotted skunk mates in late winter

behavioral isolation

unique behavioral patters and rituals separate species

example: the blue footed boobies will only mate after a courtship ritual

mechanical isolation

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

example: snails can have varying spirals on shells, which prevent mating

gametic isolation

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

example: the sperm and eggs of red and purple sea urchins are released in the water, but they cannot fertilize each other

postzygotic barriers

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

three types:

reduced hybrid variability

reduced hybrid fertility

hybrid breakdown

reduced hybrid fertility

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

example: domestic sheep can fertilize domest goats, but the hybrid embroyo 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

example: a male donkey and a female horse can mate to procude a mule, but mules are sterile

hybrid breakdown

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

example: farmers have tried crossing different types of cotton plants, but after the first generation, the plants do not produce viable seeds

micro and macro evolution

speciation is a bridge between the concepts of microevolution and macroevolution

microevolution

change in allele frequencies within a single species or population (natural and sexual selection, genetic drift, gene flow)

macroevolution

large evolutionary patterns (adaptive radiation, mass extinction)

stasis

no change over long periods of time

pace of speciation

evolution and speciation can occur at different speeds

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 accumlate differences resulting in the formation of a new species

adaptive radiation

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

convergent evolution

two different species develop similar traits despite having different ancestors

• analagous traits

extinction

the termination of a species

extinctions have occurred throughout Earth’s history (5 mass extinctions)

human activity has affected extintion rates

anytime there is ecological stress, extinction rates can quicken

if a species does go extinct, it opens up a niche that can be exploited by a different species

origins of life

Earth formed approximately 4.6 billion years ago (bya)

early earth was not suitable for life until 3.9 byaa

earliest fossil evidence is 3.5 bya

• cyanobacteria

how did life arise

early earth contained inorganic molecules

these could have synthesized organic molecules due to free energy and abundant oxygen

• organic molecules could have also been transported to Earth via meteorites or other celestial events

experimental data

oparin and haldane hypothesized that early Earth was primarily composed of hydrogen, methane, ammonia, and water

stanley miller and harold urey tested the hypothesis in their lab

• they found organic compounds and amino acids formed

experimental data cont

miller and urey 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