Kaplan MCAT Biology Ch. 16: Evolution

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evolution

process of adaptation => genetic diversity and new life forms

theory

accomplished by natural selection, mutation, genetic drift, and genetic shift

explains origins of species

ways evolution is accomplished

natural selection, mutation, genetic drift, and genetic shift

Lamarck's Inheritance of Acquired Characteristics Theory

-concept of use and disuse

-older => newer

-organs used develop, organs not used atrophy (small size) => acquired characteristics => new, more complex species

wrong => traits are inherited, NOT ACQUIRED

use and disuse

organs used develop, organs not used atrophy

acquired characteristics

Organs used develop, organs not used atrophy => CHANGES

Darwin's Natural Selection Theory

1. organisms => offspring => few survive to reproductive maturity

2. chance variations of indie in pop => inheritable => advantage => favorable

3. greater favorable => reproductive age and produced offspring => inc. traits in future generations => natural selection => sep. of organisms into distinct species => fitness, directly related to genetic contribution to next generation

inheritable

chance variations of indie in pop may be this

if advantage => favorable

natural selection

greater favorable => reproductive age and produced offspring => inc. traits in future generations

this is process, mech of evolution

survival of fittest => favorable genes in gene pool, freq. inc

chance variation result from mutation and recombination

"selected" by environment => surivive to reprod. age

only method capable generating stable evolutionary change over long periods of time (thousands to millions of years) (opp to microevolution)

fitness

reproductive success of individual

neodarwinism (the modern synthesis)

accepted theory

gene changed due to mutation and recombination => favorable => pass

opp = differential reproduction => pervasive in gene pool => pop, NOT INDIE, evolve

differential reproduction

after time, traits passed by more successfully becomes pervasive in gene pool

gene pool

sum total of all genes from individuals in population at a given time

changes over time => population, NOT INDIE evolves

punctuated equilibrium

research on fossil => change in species in rapid burst

contrast to Darwin's theory

evidence of evolution

palelontology, biogeography, comparative anatomy, comparative enbryology, and molecular bio

palelontology

radioactive dating => relating anatomies and relative abundance => fossil age => chronological succession of species

biogeography

evo not equal around globe => evo in isolation = species divergence

divergence

part of biogeo evidence

species come about from evolved in isolation

comparative anatomy

comparing similar structures => degree of evo similarity

1. homologus, analogous, vestigal structures

homologus structure

even if don't have similar appearance, shape or form => similar in structure and share common evolution origin (bat wings and human arms => forearm sim. among mammals)

analogous structures

evolved separately in each species

sim. purpose but not related origin

bird and insects => developed unique mech

vestigial structures

remnants of organ lost ancestral function

tailbone => tail for balance. human walking

comparative embryology

see sim. between embryos of diff. species => evo patterns

molecular bio

DNA can mutate => compare DNA sequence between diff. species => degree of sim.

more tax distant => amount shared dec.

indirectly comparing DNA seq => compare protein structures

genetic basis of evo

generate diff at level of genome => through:

1. mutations
2. random base changes in DNA sequence
3. recombo, novel gen combo from sex reproduction and crossing over

hardy-weinberg equilibrium

when pop not changing => gene pool is stable => no evo

Five conditions:
1. large pop
2. no mutations that affect gene pool
3. mating between individuals in pop is random
4. no net migration of individuals into or out of pop
5. genes in pop are all equally successful at reproducing

predict allelic and phenotype frequences

p + q = 1 (freq of allele in pop)

p^2 + 2pq + q^2 = 1 (freq of phenotype in pop)

gene freq constant from gen to gen if no microevolution; same as parent

x2 many alleles in pop as there are individuals

microevolution

mutations in human genome about once every 10 million BPs during DNA replication

changes in pop over short period of time (ten to hundreds of years)

5 agents of microevolutionary change

1. nat. selection
2. mutation
3. assortive mating
4. genetic drift
5. gene flow

mutation

changes allele freq in pop => shift gene eq.

assortive mating

mating not random => genotype affected => depart from Hardy

on avg, allelle freq in gene pool remain unchanged

genetic drift

changes in composition of gene pool due to chance

more pronounced in small pop => founder effect => from reproductive isolation from natural barriers or catastrophic events

Models of Natural Selection

stabilizing, directional, and disruptive selection

by diff. environment

stabilizing selection

narrow range

eliminate extremes

ex: human birth weight

directional selection

an extreme phenotype

ex: few bacteria resistance

disruptive selection

both extremes


ex: common ancestor medium beak size => large and small only

altruistic behavior

indie endure sacrifices to benefit others => altruistic

T1: gene led certain indie to not to reproduce => doesn't work since couldn't pass on

T2: kin selection => neo-Darwinism
-inclusive fitness

altruistic

large class sterile => work to benefit colony

kin selection

organisms behave altruistically if closely related to successfully reproducing organisms

consistent w/ neo-Darwinism

inclusive fitness

# of alleles that indie passes to next gen, even if indirecly through altruistic behavir

speciation

new species => indie interbreed freely but not w/ other species

reproductive isolation from same species before => diff afte

reproductive isolation

same species time pas => diff species from living in diff. places

either prezygotically or post zygotically

reproductive isolation can be either

prezygotically or post zygotically

prezygotically reproductive isolation

prevent form zygote completely

postzygotically reproductive isolation

gamete fuse but yield either inviable or sterile offspring (horse + donkey = > mule)

prezygotically isolating mech list

1. behavioral isolation
2. ecological isolation
3. temporal isolation
4. gametic isolation
5. reproductive isolation

temporal isolation

2 species => breed diff season or times of day => no interbreed

ecological isolation

2 species, same territory, diff habitats => rarely meet => rarely mate

behavioral isolation

2 species not sex attracted because diff like pheromones (chem sig) and courtship displays

reproductive isolation

genitalia 2 species not compatible => can't interbreed

gametic isolation

intercourse, but no fertilization

postzygotically isolating mech list

1. hybrid inviability
2. hybrid sterility
3. hybrid breakdown

hybrid inviability

gen. incomp. of 2 species => fertilization => abort hybrid zygote development

hybrid sterility

hybrid offspring sterile => can't make functional gametes

hybrid breakdown

1st gen hybrid = viable and fertile

2nd gen hybrid offspring = inviable and/or infertile

potential hybrid breakdown when closely related but repro. isolated species introduced => more in plants than animals

adaptive radiation

single ancestral species => # of diff species => each has unique eco niche

rapid evolution

dec. competition for limited resources

ecological niche

single ancestral species => # of diff species => they each occupy

when looking at similarities between 2 species

sim. in sharing common ancestor OR sharing common environment w/ same evo. pressures

3 patterns of evo

1. convergent evo
2. divergent evo
3. parallel evo

convergent evo

indie develop sim. characteristics in two or more lineages not sharing common ancestor

ex: dolphins and fish have sim. physi, but diff class of vertebrates

divergent evo

indie develop of dissim. characteristics in 2 or more lineages sharing common ancestry

ex: seals and cats => both mammals same order, but dif in appearance => diff environment, diff selection pressures

parallel evo

response to environment => related species evolve in sim. way for long period of time

origin on life

earliest evi is stromatolites, which photosynthetic bacteria = prim. prokaryotes

early earth => organic molecules (AA) => planet had high amounts of C, H, and N and less O (primordial soup) => w/ massive energy from many sources => bonds formed between atoms

exp w/ electrical discharge => simple AA => further => 20 AA, lipids, and all 5 N bases

formation of protobionts (origin on life)

abio produced polymers in aq. sol assemble spon. into tiny proteinaceous droplets called microspheres => selectively permeable membrane

collodial droplets (coacervates), sol of PP, NA, and polysac => carry enzymatic activity w/in membrane if enzymes and substrates are prsent

coacervates and microspheres NOT living cells

collection of organic polymers thought primitive ancestors of living cells are called protobionts

formation of genetic material (origin on life)

-believed short strands of RNA 1st molecule self rep (can align w/ comp bases on short RNA seq and bing together => new short RNA chain) => asso. of AA w/ specific RNA bases => AA together in particular sequence and facilitate bonding => particular peptide => heredity mech => protobionts grow, split, and transmit => self rep for molecules needed by primitive cells => DNA, more stable than RNA

-N.S probably favored RNA seq. whose 3D more stabl and rep faster
-syn pep enhancing rep and/or further activity of RNA

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