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63 terms

Kaplan MCAT Biology Ch. 16: Evolution

process of adaptation => genetic diversity and new life forms


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
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)
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
radioactive dating => relating anatomies and relative abundance => fossil age => chronological succession of species
evo not equal around globe => evo in isolation = species 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
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
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
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
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