- adaption and genes respoble for them only need to be good enoguh for reproduction ; increase fitnees but doesnt make a function any better than it musts; adequcy not perfection
2.natural selection has no goals not looking for progreess or speicifc outcomes
3. only acts on exisiting variation doesnt creat optimal variation that cames from random geentic mutation
4. historical constraints limits it, prior adaption may limit future adaptabilty when selective pressures change
5. adaption are comporomises, pops are subject to many possibly opposing sleective pressures
6. chance events (genetic drift, gene flow) environemtn variabilty limit natural selection
change in allel frequences. in popualtion over generation
evolve via natural selection
smallest unit of evolutioanry change
- group of individuals of the SAME SPECIES that live in the SAME AREA and INTEBREED, producing FERTILE offspring
consists of 2 alleles in diploid indivudals
differnt forms of a gene corresponding to diffrent dna squences in each form
-1 allele per chromosmes
-in sexually reproducing diploid species, 1 chromosome from each parent
-each allele remain seperate no blending, apparent blending is from incomplete dominance
different combinations of alleles from the gene pool: all alleles present in all individual in the population
- geogrpahic isoaltion; distinct gene pools even if same species
- in heritable traits is prerequisite for evolution
- one of the 2 main components of biodiveristy
-advantgeous to a pop bc it enable adaption of pop to environemnt via NS
- caused by difference in genes or other dna segmetns (indiviudal shave specific genotype; combination of alleles)
-product of inherited genotype and enviornmental influences
-NS can only act on variation with a genetic component
-not all phenotypic variation is heitable
mutation and sexual reproduction
changes in individuals dna sequence caused by small scale (point mutation) or chromosomal (isnertion/deletion) in dna replication or strucutral damahe to dna (radiation)
- only mutation in cells that produce gametes are hertiable
- OCCUR RANDOMLY (no effect from selective pressures)
- CREATE NEW ALLELES
- single mutation can have no effect/change in phenotype or can be lethal (most have no effect)
- mutation can be bad, neutral or advantegous in the current situation
- mutation rates ar elow in animal and plants, human genomes have 60-100 mutations per generation, much lower in porkarytoes but accumatle quickly because thye have short generation times
- most eovlutionary change is based on accumation of many mutation with small indivual effects
-chromosoal, dupilcaiton od small dna segments, whole gneome duplication
that delte or rearrange many loci are typically harmful
increases genome size usually less harmful, can result in duplication of genes that can take on new function by further mutation
process of genome doubling is an important driver of evolution by supplying genetic material and increasing genome complexity
can shuffle exisitin alleles into new combinations, radnom mating--> random fertilization
-recombination of homolgocous chromsoms during meisos shuffles exisiting material to create new combinate of alleles
- more important for genetic variation in sexual reproducing organisms
natural selection, genetic drift and gene flow
caused only by natural selection, where a population becomes more adapted to its environment
any change in allelfrequency that doesnt evolve to more adapted pop
genetic drift and gene flow since their effect on alelel frequences are priamrily random
* mutations and recombination are also non adaptive but they DONT IMPACT allele frequences
feeature or trait (selected through natural selection) provides advantge to individual
contribution an individual makes to gene pool of next generation realtive to other contributions
directional
disruptive
stabilizing
DDS
favours individuals that differe from the curren mean phenotype of a population in 1 direction, goes to one extreme end
- pop genetic variance shift toward new phenotype w higher fitness when exposed to pressures
- response to consitent selective pressure
- frequency distrubtion of phentype shift, shift into mean of pop, DOES NOT affect amount of genetic variance in pop
- favours individuals at both extremes of the phenotypic range, avergae phenotypes are less fit than extremes
- results in 2 or more divergent phenotypes
- MAINTAINS GENETIC VARIATION
ex. beak size in the black bellied seedcracker of west africa, either exteremly small or extremely large beaks
favours intermediat or common variant by selecting gasint extreme phenotypes that deviate from curren tpop mean
-conserve functional geentic features by selective pressures agasint bad variants
- mean of pop stays the same, genetic variation DECREASES
- no evolutinaory change, very common tho remvoign delterious mutations
random changes in alelle frequency
- fluctuae undpredicatbly from one gen to the next
- MORE LIKELY IN SMALL POPS
- random events can remove certain alles, rare alleles more likely to be lost
- REDUCE genetic varaiton becuase allels are lost
- cause evolutionary change but is non adaptive
- largest impact on small pops
- causses random allel frequency changes
- can lead to loss of genetic variation in pop
- can cause harmful allels to become fixed in small pop
founder effect
bottle neck effect
sudden reduction in pop size due to enviornment change, pop size reduced within its natural range, ex. catstrophe destroys most of pops habitat
- only few indiviudal can cotnribute allels to next gen, allel frequency for next gen is diff than previous, if it remains small it can be further affected by genetic drift
EXAMPLE: greater prairei chickens, loss of habitat, bottle neck reduced genetic variation --. loss of genti cidversty--> loss of fertility
when few individuals become isolated from a larger pop
- allel frequency in original remains unchanged
- small found pop has a small fraction of total gene pool, ex. inc frequency of huntington disease in human pop from small group of european migrants
movement of alleles between popualtions of species
- can be trasnfered through mvoement of fertile individals (dispersal of animals or seed) or gametes (pollen)
- can INCREASE variation only into recieving popopulation -counteracts genetic drift but may slow adaption of recieving population
-REDUCED variation between pops over time becuase they become more similair with each other
-can decrease fitness of receiving popular, when the immigration of allels decrease fitness is more rapid than natural selection for advantgeous alles, continously introduce maladaptive allels into loc pops (water snak pop of lake erie)
- it can also increase fitness when gene flow suppplies new allels to pops w limited variation (ex spread ofalle to resitance to isnectidies)
extripation of populations reduced gentic divertsy of a species
- global extinction of species (complete loss of gentic diversty)
- neutral vartion: variation that doesnt give a adavantge or disadvantge does not affect frequency of neutral mutations also
- mutation
-recombination (crossing over of chromosmes during meiosis)
- independent assortment of allles during meiosis
-random mating of organisms (sex)
-random fertilization (sex)
- recessive allels are hidden from selection in heterozygote indviduals
-disruptive selection (natural selection)
- gene flow (between pops)
- balancing selection
prior to darwins work, earth was viewed as geolically young inhabited by unchangin species
linnaeus believed simlarites between organisms relfeted their pattern of creation
fossisl, found in sedimetary rack which appears in stara (layers0, other had noted fossil did not remseble living ones so extinction of species must occur
french naturalist, noted fossils from older straa are different than licing organisms and that fossil species changed between strate (extinction)
he proposed catasrophism
each boundary between stara represent catasrophic event
- he beleived species did not change over time; no evolution
the succesion of life form in the earth stra were due to catastrophe--> local extinction--> presence of fossils
- after. catastrophe different species move into area--> new fossil in a new stratum
french zoologist
- apparent dissapernace of species was on species was slowly changing into another he was philosphiccally opposed to extinction
- he thought species evovled through the inheritance of aquired chracterstics: an organism can pass on characterstic it had during its lifetime to ists offspring (use/dissue of strcuutre lead to heritable change)
- not plasubile for evolution not supported by geenetic inheritance or evidence (mice tail cutting still grw tails)
1) species show evidence of descent w modification from common ancestores (all organisms are rleated through decent from an ancestor) he never used the word evolution in the first editon
2) natural selection is the emchanism for descent with modification
process by which livign organism descend with modification from ancestors
explains the duality of unit and diversity in livign organims
simialr traits among organism from commmon ancestor, difference are due to accumation of heritable changes
during the voyage of hms beagle, darwin sw many examples of adaptions; inherited characetsic of an organism that enchances its survival/reproduction, he realized adaption and the orign of new species were closey related
- galapagos finches demostrae connection between adaption adn speciation
finch species on different galapagos islands were similar yet had distinct difference
- simialr appearnce of finches from 1 island or habitat to another is unity from common ancestry, they were dissimalr in beak shape adaption because of theri food sources and feeding
darwin hypothesided th ebeak of ancestral species had adatped over time to form descent species that adapted to different. food
- galapagos finches form a MONOPHYLETIC group, they descend from a single common ancestor
darwin proposed this as the mechanism for descent w mod, he noted humans have modified other species by selecting and breeding indivudals with desired traits; artifical selection
-members of a pop vary in inherited traits
- pop produce more offspring than the environment can support and many of these offspring fail to survive and reproduce. (insuff resources--> comp for resources)
writng of the econmist thomas malthus
individuals whose inherited traits give them higher porbailty of surving and reproducing in a given environment leave more offspring than other individuals
the unequeal abilty of individuals to survie and reprduce will lead to accumation of favourable traits in the pop over gens
individuals avry in heritable traits and there competion for resources from overproduction of ofspring, difference in reproductive success of individuals because some traits are better then these better traits are favoured and accumatle in the pop
genotypic variation
phenotypic variation
genotype: genetic makeup of indivual
- gene varation is difference in dna among indivudal in a popualtion, it is heritbale
phenotype an organism observable charactestics (morphology, pysicogical/biochemcial properties and behaviour)
- phenotypic varaiton is the variabilty in phenotypes that exists
- an organisms phenotype is determined by interaction of environmental factor and its genotype sometimes it is soley determined by the environment and not heritable (flower in a certain soil0
seen by the environemtn, expressed in th ephenotype and be heritable (caused by gennotype)
- gentic vartiaon ariss radnomly but NATURAL SELECTION IS NOT A RANDOM PROCESS
environemtnal factors acting on pops to effect the survial / reproduction of indiviudals in the pop--> selctive prssure
- biotic (predators, disease, competitiors) and abitoic (space light temp water)
no natural selction without selective pressure
- substanial popualtion varies in beak depth
- drought happens which reduces number of small seeded plants, so insuffcient food, finched had to compete for larger seed which are harder to open and needed bigger beaks
- offspring of finches survived the drougth had greater beaks than the original pop
truth all that is needed is greater reproductive sucess
- indidivuals w benefical inehrited traits survive and reproduce at higher rate than other indivudals
- increases adaption of pop over time in their environment
- only popualtions evolve not inddivuals; adaptions changes the proption of beenfical traits across mutliple generatons
- natural slection acts on existing variation does not create new traits