Unit 7 - Natural Selection Flashcards
adaptation
inherited characteristics (phenotypes) that enhance survival and reproduction
evolution
characterized by a change in the genetic makeup of a population over time
darwins argument: variation
- variation exists in populations; variation is an inherited trait.
- inference: individuals that are beter adapted to their environment will survive and reproduce
darwins argument: more than survive
- more individuals are born than can survive
- inference: unequal ability for individuals to survive leads to favorable phenotypes to increase in frequency over generations
fitness
- measure of a traits survival and reproduction
- HIGH FITNESS: survive and reproduce
what happens if the environment changes?
natural selection
natural selection
traits that are better adapted (higher fitness) will be able to continue through a population
- amplify traits
natural selection results from
- predators
- lack of food
- adverse physical conditions (temp, pollution)
- gradual changes accumulate and less favorable will diminish
ex: the peppered moth
in the 1850’s, soot covered many trees in England; therefore, peppered moths phenotype frequency decreased as it didnt blend in with surroundings
can an individual choose to change its phenotype to suit its environment?
no, this happens overtime
can an organism just adapt by mutating?
no
does the environment cause a mutation to occur?
no
what happens if a population lacks genetic variation (therefore no phenotypic variation) and the environment changes
possible extinction
what happens if a mutation arises in an offspring that results in an adaptation (an inherited characteristic) that increases the chance of surviving and reproducing?
the trait will be passed onto future populations
ecological niche
an organisms role in its ecosystem
ex: bees polinate
3 outcomes of natural selection
- stabalizing selection
- directional selection
- diversifying selection
stabalizing selection
- selection towards the median
directional selection
- a shift
diversifying/disruptive selection
- moving to extremes
artificial selection
- humans select for desirable traits in future populations
ex: dog phenotypes
natural selection
- nature selects for the adapative trait
- competition is our selective pressure
positive selective pressure
- trait is selected for??
ex: antibiotic resistance
negative selective pressure
- genetic disease????
- protein malfunctions
- reduces the occurence of disadvantaegous traits
what do natural and artificial selection have in common?
changing phenotypes over time
artifical selection
- humans are the selecting agent
convergent evolution
different species have similar traits but do not share a common ancestor; this is due to similar environmental pressures
ex: butterfly wings, bat wings
divergent evolution
- similarities are due to a common ancestor
convergent similarities are due to
similar environmental pressures
population genetics: nonrandom
- natural selection
- sexual selection
population genetics: random
these are mechanisms throufh which populations can evolve: mutations, genetic drift, gene flow, bottle neck effect, founder effect
what does it mean to evolve
change in allele frequencies in populations over generations
confers
gives
sexual selection: interdependent
- female choice
- leads to sexualdimorphism
sexual selection: intradependent
- male competition
- leads to sexualdimorphism
sexualdimorphism
- males look different from females
what is the ultimate source of variation????
mutations
genetic drift
- a random change in the frquency of alleles in a population over time, happening by chance (due to bottleneck, founder)
bottleneck effect
- a disaster wipes out a large number of individuals so variety is lost
- most harmful to smaller populations
founder effect
- some individuals leave the main population and migrate to a new area and begin to reproduce
gene flow
- new individuals move into an area (migration)
key idea: not all mechanisms of evolution are ADAPTIVE, some are RANDOM
how can we measure if population is evolving?
hardy weinburg
what are the 5 mechanisms of evolution
natural selection, sexual selection, mutations, genetic drift, gene flow
what does it mean if a population is in Hardy Weinburg Equilibrium?
NOT evolving from one generation to the next
- no natural selection can occur
- random mating
- no mutations
- large population size
- no migration/gene flow
evolution: allele frquencies
- evolution is a change in allele frequencies over time; we need a formula to calculate these frequencies in a population
p + q = 1
- this formula has to do with how many dominant or recessive alleles r in the gene pool
p^2 + 2pq + q^2 = 1
used when talking about individuals/genotypes in a population NOT allele frequencies
evolution is supported by scientific evidence from many disciplines
- geographical
- geological
- physical
- biochemical
- mathematical
geographical evidence of evolution
- distribution of organisms around our planet
- pangea: you can see divergent and convergent evolution (how they changed after pangea)
geological evidence of evolution
- fossil evidence: tells us when an organism lived, how it lived, changes over time
physical evidence of evolution
- homologous structures: similar structures, different functions (divergent evolution)
- analogous structure: similar structures and function (convergent evolution)
biochemical evidence of evolution
- examine DNA, proteins, Amino Acids, RNA
- the more in common, the more closely related
mathematical evidence of evolution
hardy weinburg - look at allele frequencies of poplations
fossil record
- oldest will be at the bottom of a cross section, youngest at the top
- vestigial structures: no longer used structures in organisms
morphological homologies
- embryology: embryos develop similarly
KEY IDEA: structual and functional evidence supports the relatedness of organisms in all domains
processes that are conserved across organisms
- Glycolysis: makes ATP
- DNA replication
- Protein Synthesis
structural and functional evidence
- DNA
- cell membrane
- proton gradient to make ATP
explain how evolution is an ongoing process in all living organisms
because populations keep changing over time due to mutations (random changes in DNA happen all the time), natural selection, genetic drift, gene flow (individuals move between populations)
antibiotic resistance
- antibiotics usually target specific proteins / enzymes made by bacteria
- if bacteria makes a different shaped enzyme then antibiotic cannot work against it
pesticide resistance
- pesticides usually target specific protiens / enzymes made by the pest
- if pest makes a different shaped enzyme, the pesticide cannot work against it
phylogenic trees and cladograms
- used to show evolutionary relationships
- based on morphological and biochemical data
crevice of cladograms
- AKA: node
- point of divergence or common ancestor
does arrangment of cladograms matter? what does?
no, but look for the same nodes
if asked, using a cladogram, the second most recently evolved species is more closely related to that before or after it?
after it, AKA, the most recently evolved
what is a species
organisms that can mate (interbreed) and produce viable & fertile offspring
reproductive isolation
- when two groups do not mate together (cannot mate together)
what would prevent two organisms from mating?
prezygotic factors
prezygotic factors
- geographical isolation
- habitat isolation
- behavioral isolation
- temporal isolation
- gametic isolition
- mechanical isolation
post zygotic factors
- reduced hybrid fertility
- reduced hybrid variability
- hybrid breakdown
geographic isolation
- species are in different geographical locaitions; therefore, mutations will evolve independently
habitat isolation
- organisms living in different habitats
ex: organisms near water at the beach vs organisms near dunes
behavioral isolation
- mating or courtship behaviors
temporal isolation
T - time
- different mating time; seasonal, monthly, day vs. night
gametic isolation
- sperm and egg do not fuse
mechanical / physical isolation
- physical isolations seperate them
ex: giraffe and pig
allopatric speciation
- geographical speciation
sympatric speciation
- habitat isolation - same region
postzygotic barriers
- prevents zygotes from developing into viable, fertile, offspring
postzygotic barriers: reduced hybrid fertility
- hybrids may be viable (strong and sterile, live life as normal) but they are sterile due to different chromosome numbers from the two parents
postzygotic barriers: reduced hybrid viability
- parents have incompatible genetics and offspring fails to develop
gradualism
- evolution by natural selection as presented by Charles Darwin
- hypothesis: slow changes over long periods of time
punctuated equilibrium
- long periods of little/no change followed by rapid bursts of speciation (caused by ecological stress)
- hypothesis: rapid change followed by long periods of no change
divergent evolution
- when populations become separated by geographic barriers and evolve independently into their own species. they evolve in their respective habitats and become more different from each other over time
adaptive radiation
- type of divergent evolution where a group of organisms quickly diverge into new species. new species radiate from a common ancestor. this tends to occur when organisms move into a new environment with a lot of open niches
what can fossil records be used for
- can be used to observe what organisms lived at different times
- can also see mass extinctions
why do organisms go extinct
- environmental stress
- organisms are outcompeted
- natural disaster
- lack of genetic variation
- depletion of resources
KEY IDEA: the level of variation in a population affects population dynamics
population dynamics
- portion of ecology that deals with the variation in time and space of population size and density for one or more species
genetic variety in relation to extinction
- populations with less genetic variety are more at risk of extinction (decline)
how does the level of variation in a population affect the population dynamics
increased genetic variety increases the resilience of the population
alleles that are adaptive in one environment can be harmful in another due to selective pressures
ex: peppered moths
origins of life on earth
- earth is about 4.6 billion years old
- archaens are the first living organisms
- no O2
why dont we have rocks from 4.6 billion years ago??
the environment was very hostile, earth was basically a giant ball of lava, the rocks would’ve melted
two theories of origin of life
- primordial soup
- extraterrestrial origin
what is the basic unit of life on earth
cells
what are cells made of
macromolecules: proteins, lipids, carbohydrates, protiens, nucleic acids
what are macromolecules made up of
C, H, O, N, P, S
did early earth contain the elements to build the chemical precursors to life on earth
yes - proven by milley urey experiment that successfully produced amino acids from inorganic molecules
what do we know about earths early atmosphere?
it was a reducing atmosphere because of H+ (gaining electrons)
miller urey experiment
- early Earth’s atmosphere was able to give rise to amino acidse
primordial soup theory
earth had a rich “soup” of organic molecules formed from inorganic compounds in the absense of O2
extraterrestrial theory
- our amino acids / complex molecules came from asteroids/meteorites
evidence of extraterrestrial
tagish meteor - 2000
scientists hypothesize that the first cells were ______ which meant they
- autotrophic
- were able to make glucose from formaldehyde
scientists hypothesize first cell membranes were not phospholipids but ______, like bubbles.
- fatty acids
- called protobions
RNA world Hypothesis
- all organisms at one time used RNA not DNA
evidence: RNA carries out chemical rxns (DNA does not)
evidence: ribosomes are made of RNA
cyanobacteria
- first photosynthetic organisms
key concepts of darwins theory of natural selection
- individuals do NOT evolve; populations evolve
- an individual organism does NOT change to adapt to its environment
- involves enormous amount of time
IMPORTANT!!!!!! natural selection is…
situational – what may be advantageous in one situation can be detrimental in another
what is the strongest evidence that all living things share a common ancestor
- universatality of the genetic code
artificial selection is also known as
selective breeding
homologous structures
- same structure
- different function
- divergent
analogous structures
- different structure
- same function
- convergent
species
a group of similar organisms that can breed and produce fertile offspring
speciation
process whereby a new species arises
where does the variety come from that the natural selection acts upon?
the variation comes from crossing over, independent assortment, random assortment of gametes, etc
genetic drift
- chance changes allelic frequencies
what are two events that shrink opulation down to a size that genetic drift has a large effect?
- bottleneck
- founder effect
the founder effect
- type of genetic drift that involves small groups of organisms separating from larger population and forming small new colonies
- genetic variation is limited
bottleneck effect: do the survivors represent the original gene pool??
- natural disaster kills off many organisms
- survivors not necessarily representative of the original gene pool
gene flow
migration
- think of british going to india and mating???
speciation is very difficult due to
- reproductive isolation
prezygotic: populations live in diff habitats, no sexual attraction, mate at diff times.
zygotic: structural diff in genitalia, gametes fail to attract eachother
postzygotic: hybrid zygotes fail to develop, hybridds cant make their own gametes, reduced fertility
types of speciation
- allopatric
- sympatric
- adaptive radiation
**based on how gene flow is interuptted
allopatric speciation
- populations segregated by a geographical barrier
ex: island species
sympatric speciation
- reproductively isolated subpopulation in the midst of its parent population
punctuated equilibrium
- thought to be the correct mode of speciation
- there is NO GRADUAL TRANSITION of fossil forms; species appear as new forms then suddenly disappear
why can going off of phenotypic similarities be unsuccessful for constructing cladograms
- structures may be analogous, meaning they are not homologous therefore not closely related; do NOT have a recent common ancestor
outgroup
- least related species
- serves as a reference point
hardy weinberg equilibrium model is the model of a gene pool of a
nonevolving population
hardy weinberg equilibrium follows that frequencies of alleles and genotypes in a population remains
constant over generations
milley urey experiment states that
- original evolution of life or living organisms from inorganic or inanimate substances
- atmosphere must be reducing (bc no oxygen)
