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BIOLOGY--UNIT 4 Cheat Sheet by

evolution of populations, origin of species, broad patterns of evolution

BROAD PATTERNS OF EVOLUTION

Evolution occurs at the population level, evolut­ionary impact of natural selection is seen in how a population changes over time.

THE EVOLUTION OF POPULA­TIONS

evolution
changes in allele frequency
allele frequency
(all add up to 1)
population
group indivi­duals of the same species that live in the same area & interbreed to produce fertile offspring
genetic variation
differ­ences in genen compos­ition
sources of genetic variation
sexual reprod­uction
 
mutation (change in nucleotide sequence)
 
point mutations (single nucleotide change) ex. sickle­-cell
 
delete, disrupt, duplicate, rearrange loci
genetic variation is required for evolution, but does not guarantee a population will

CHANGE IN ALLELE FREQUENCY

 
effect on allele frequency
causes
genetic drift
unpred­ictable fluctu­ation of alleles, reduces genetic variation, can limit natural selection
founder effect, pop. bottleneck
founder effect
few indivi­duals isolated, diff. allele freque­ncies in small founder pop.
chance
bottleneck effect
reduced genetic variation and increased frequency of harmful alleles
sudden enviro­nmental change
3 mechanisms change allele frequency = genetic drift, gene flow, natural selection (consi­stent adaptive evolution)

SEXUAL SELECTION

what is it?
indivi­duals w certain charac­ter­istics are more likely to find mates
sexual dimorphism
marked differ­ences between sexes (ex. pavo real)
intras­exual selection
selection within same sex for mates
inters­exual selection
one sex is choosy with mates
sexual selection is natural selection for mating success

NATURAL SELECTION MODES

direct­ional
conditions favor indivi­duals at one end of the phenotypic range
disruptive
conditions favor indivi­duals at both extremes of phenotypic range
stabil­izing
conditions favor interm­ediate variants
natural selection consis­tently causes adaptive evolution by acting on phenotypes

Hardy-­Wei­nberg Principle: Equili­brium Population

condition
conseq­uence if condition is not kept
1. no mutations
gene pool is modified
2. **random mating
inbreeding = no random mixing of gametes, genotype freque­ncies change
3. no natural selection
allele freque­ncies change
4. very large pop. size
in small pop. allele freque­ncies change by chance (genetic drift)
5. no gene flow
gene flow can alter allele freque­ncies

CAUSES OF EVOLUTION

DEFINITION OF SPECIES

concept
defines species by
biological
reprod­uctive compat­ability
reprod­uctive isolation → new species
gene flow between popula­tions holds gene pool together, species pop. resemble each other
limita­tions
gene flow between morpho­log­ically & ecolog­ically distinct species (ex. grolar bear)
morpho­logical
structural features
ecological
ecological niche, intera­ctions w nonliving and living enviro­nment
based on potential to interb­reed, not physical similarity

THE ORIGIN OF SPECIES

speciation
one species splits into two or more species
speciation rates
range from 4,000 y to 40 million y (avg. 6.5 my)
allopatric
geogra­phi­cally isolated popula­tions
 
population -gene flow interr­upted→ subpop­ulation
 
mutation, genetic drift, natural selection, reprod­uctive isolation
reprod­uctive isolation
can't breed bc of differ­ences
behavioral isolation
prezygotic barrier, specific mates
sympatric
population (no geographic barrier)→ new species
 
reprod­uctive barrier, reduced gene flow
 
polypl­oidy, habitat differ­ent­iation, sexual selection
polyploidy
extra chromo­somes
 
auto: same species allo: diff species
habitat differ­ent­iation
new ecological niches
sexual selection
female selecting mates
microe­vol­ution (speci­ation)
many specia­tions, extinc­tions → macroe­vol­ution

SPECIATION MODELS

punctuated = rapid speciation gradual = slow speciation

REPROD­UCTIVE ISOLATION

reprod­uctive barriers
depend on enviro­nmental & genetic factors
Prezygotic Barriers
prevent mating between species
 
geogra­phical
physical barrier (rivers, mountains)
 
habita­t/e­col­ogical
same area, diff habitats
 
temporal
diff breeding times
 
behavioral
unique courtship rituals
 
mechanical
morpho­logical diff
 
gametic
cannot fertilize
Postzy­gotic Barriers
prevent a viable, fertile hybrid
 
reduced hybrid viability
poor develo­pme­nt/­sur­vival
 
reduced hybrid fertility
fertile hybrid
 
hybrid breakdown
infertile 2nd gen
Hybrid Zones
diff species mate, incomplete reprod­uctive barriers
novel genetic variation outcomes = *
reinfo­rcement
hybrids cease
← hybrids less fit
fusion
two species fuse
← weakened rep. barriers
stability
continued hybrids
← hybrids equally fit
biological barriers that impede fertile offspring

THE GEOLOGIC RECORD

TECTONIC PLATES THEORY

continents are part of plates of Earth’s crust, floating on hot mantle

3 occasions (1 billion, 600 million, and 250 million years ago) when most of the landmasses of earth came together to form a superc­ont­inent

HISTORY OF EARTH

FOSSILS

fossils are the traces of ancient life, naturally preserved, but an incomplete chronicle of evolution
macroe­vol­ution
evolution above the species level, inters­pecific variation
microe­vol­ution
evolut­ionary change in allele freque­ncies in a population over genera­tions, intras­pecific variation
favor species that existed for a long time, were abunda­nt/­wid­esp­read, had hard shells, skeletons

FOSSIL FORMATION

FOSSIL DATING

relative age determined by rock strata sequence
younger stratum has more recent fossils
older stratum has older fossils
absolute age determine through radiom­etric dating
radioa­ctive "­par­ent­" isotope decays to "­dau­ght­er" isotope at a constant rate
half-life
known time required for half parent isotope to decay

RADIOM­ETRIC DATING

If the half-life of carbon-14 is about 5,730 years, then a fossil that has 1/8th the normal proportion of carbon-14 to carbon-12 should be about how many years old? 5730 Years X 3= 17190 years

CREATIONS ACCORDING TO FOSSILS

earliest prokaryote fossils
(ARCHAEAN EON)
form stroma­tolites dating back 3.5 BYA,
sole inhabi­tants for 1.5 BY
increase in atmosp­heric oxygen
2.7 BYA
cyanob­act­eria, other photos­ynt­hes­izers
led to extinction of many
earliest eukaryote fossils
(PROTE­ROZOIC EON)
1.8 BYA, gave rise to multic­ellular organisms
jawed verteb­rates
(PHANE­ROZOIC EON)
440 MYA
Cambrain explosion (535-525 mya)
+diver­sity, unique mammalian features
tetrapods
(PALOZOIC ERA)
375 MYA colonized land
mammals
120 MYA, from synapsids

MASS EXTINC­TIONS

can be caused by:
Habitat destru­ction and/or unfavo­rable enviro­nmental change
Biological causes (facto­rs)­-Origin of one new species can spell doom for another
Permian Mass Extinction (252mya)
96% marine life when extinct due to intense volcanisms
Paleozoic to Mesozoic era
Cretaceous Mass Extinction (66mya)
+50% of all marine animals, many terres­trial plants and animals, dinosaurs (except birds) due to meteorite
Mesozoic to Cenozoic era
5–10 million years for diversity to recover
mass extinc­tions alter ecological commun­ities and remove lineages, forever change the course of evolution and can also pave the way for adaptive radiations

ADAPTIVE RADIATION

the evolution of many diversely adapted species from a common ancestor that allows new species to occupy different habitats
may follow:
mass extinc­tions
ex. mammals after extinction of dinosaurs
 
evolution of novel charac­ter­istics
ex. rise of photos­ynt­hetic organisms
 
coloni­zation of new regions
organisms colonize new enviro­nments with little compet­ition

CONTIN­ENTAL DRIFT DURING PHANER­OZOIC EON

Pangea (250 mya), organisms adapt (speci­ation) or go extinct

when continents drift can result in allopatric speciation

GENETIC MECHANISMS

develo­pmental genes
program develo­pment, influence rate, timing, spatial patterns
hetero­chrony
evolut­ionary change in the rate or timing of develo­pmental events
ex. human vs chimpanzee jaw
homeotic genes
determine the organi­zation of basic features
hox genes
a class of homeotic genes, provide positional inform­ation during animal develo­pment
evolut­ionary novelties
changes at the genetic level lead to develo­pmental changes at the phenotypic level
exapta­tions
structures that originally played one role but gradually acquired a different role
ex. bird feathers

EUKARYOTES ARE "­COM­BIN­ATI­ON" ORGANISMS

conseq­uence of endosy­mbiosis

PROTIST

is any eukaryotic organism that is not an animal, plant, or fungus
first eukaryote was a unicel­lular protist and most eukaryotes are protists
structural and functional diversity, most are aquatic, most are unicel­lular
complex at the cellular level, though simple when compared to eukaryotes
nutrit­ional diversity:
photoa­uto­troph = producers (photo­syn­thetic)
use energy from light (or inorganic chemicals) to convert CO2 to organic compounds
 
hetero­troph = consumers
 
parasites =
 
mixotroph =
photos­ynt­hetic protists
main producers in aquatic community
biomass of photos­ynt­hetic protists is limited by the availa­bility of nitrogen, phosph­orus, or iron
diatoms, dinofl­age­lletes, multic­ellular algae, others
blooms dramatic increase in abundance
symbiotic protists
some are parasites that harm their hosts
ex. photos­ynt­hetic dinofl­age­llets provide food for coral reefs
ex. wood-d­ige­sting protists break down cellulose in the guts of termites
effect on human health
 
trypan­osoma = excavate that causes sleeping sickness
apicom­plexans = alveolate parasites
ex. plasmodium - causes malaria

ORIGINS OF COMPLEX MULTIC­ELL­ULARITY

multic­ellular colonies
collec­tions of connected cells, little to no differ­ent­iation, can be simple or complex
Multic­ellular organisms with differ­ent­iated cells likely originated from multiple different ancestors
1. origin of cyanobacteria
2. origin of mitochondria
3. origin of plastid (chloroplast)
4. origin of multic­ellular eukaryotes
5. origin of fungal­-plant symbioses

EUKARYOTE SUPERG­ROUPS

Excavata (unice­llular protists)
diplom­onads;paraba­salids
lack plastids, cannot do photos­ynt­hesis, reduced mitoch­ondria, mostly anaerobic
euglen­ozoans
most have 2 flagella, diverse, inclue predatory hetero­trphs, photoa­uto­trophs, parasites
ex. trypan­osoma - parasitic infection that causes sleeping sickness
SAR (Stramen­opiles, Alveolates, Rhizarians)
includes most important photos­ynt­hetic organisms)
diatoms — diverse photos­ynt­hetic unicel­lular algae
can affect
brown algae (seaweed) — largest & most complex, multic­ell­ular, mostly marine
brown due to carote­noids in plastid
anchored by holdfast, stem-like stipe supporting leaflike blades
Archae­pla­stids
red algae — 2nd largest, mostly multic­ell­ular, can absorb green & blue light
red due to phycoe­rythrin pigment
green algae— very similar to land plants, some are unicel­lular
chloro­phytes — marine, terres­trial, mostly freshw­ater, multic­ell­ular, unicel­lular (free or symbiotic)
charop­hytes — most closely related to land plants
plants
chloro­plasts of land plants cyanob­acteriagreen algaeland plants

EUKARYOTE SUPERG­ROUPS

 

DIVERS­ITI­FIC­ATION OF EUKARYOTES

eukaryotes
 
a) plants
b) animals
c) fungi, molds, mushrooms, yeast
d) protists
early eukaryotes
date back 2.7 billion years ago
unicel­lular, with nucleus, membrane, cytosk­eleton, varied size & shape
diverse eukaryotes
1.8 billion years ago
novel biological features evolved: multic­ell­ula­rity, sexual life cycles, eukaryotic photos­ynt­hesis
large eukaryotes
635-541 million years ago (Ediacaran period) soft-b­odied organisms
hard-b­odied organisms 535-525 mya (Cambrian explosion)

ORIGIN OF MITOCH­ONDRIA & PLASTIDS

plastid
membra­ne-­bound organelle (plants, algae, others)
ex. chloro­plast
endosy­mbiont theory
mitoch­ondria and plastids were formerly small bacteria that began living within larger cells
key evidence
•inner membranes are similar (transport proteins) to bacteria plasma membrane
•replication is similar to bacteria cell division
•have circular DNA like bacteria
•transcribe/translate own DNA into proteins
•ribosomes more similar to bacterial than eukaryotic
mitoch­ondria come from a single proteo­bac­terium ancestor which could do aerobic respir­ation using O2 to make ATP
plastids come from a single cyanob­act­erium ancestor that could do photsy­nthesis
ALL eukaryotes have mitoch­ondria, not many have plastids
anaerobic host cells may have benefited from aerobic endosy­mbionts as oxygen increased in the atmosphere

EUKARYOTIC DIVERSITY (PHYLO­GENETIC TREE)

(protists are yellow) \

THE GREENING OF EARTH

+4 billion years ago
Earth was created, lifeless for the first 2 billion years
1.2 billion years ago
cyanob­acteria & protists
+470 million years ago
plants colonized land
500 million years ago
plants, fungi, & animals moved to land
385 million years ago
first forests

PLANTS

ancestors
red, green, & brown algae
multic­ellular
eukaryotes
photsynthetic autotrophs
cellulose cell walls
chlorp­lasts (chlor­ophyll a & b)
modernly only charop­hytes share most traits w plants
chloro­plasts of land plants
cyanob­acteria ➙ green algae (charo­phytes) ➙ land plants
moving to land...
🅐 evolution of:
sporop­ollenin ⁠— protective polymer surrou­nding charophyte zygotes ➙ dry land
🅑 BENEFITs: unfiltered sunlight, plenty CO2, nutrie­nt-rich soil
🅒 CHALLE­NGES: scarcity of water, lack of support against gravity
key traits in plants not found in charop­hytes
•alter­nation of generations
•multicellular, dependent embryos
•walled spores produced in sporangia
•apical meristems
apical meristems
localized regions of cell division @ tips of roots & shoots, mitotic division = +mineral & nutrients
derived traits
•cuticle — waxy coating, prevents water loss
•stomata — specia­lized pores, CO2-O2 exchange
plants affect soil formation, roots stabilize soil and are nutrients when they decay, 50% atmosp­heric O2

HIGHLIGHTS OF PLANT EVOLUTION

PLANT CLASSI­FIC­ATION

vascular plants
vascular tissue for H2O/nu­trient transport
xylem- conducts most H2O/mi­nerals (tracheids have lignin = water-­con­ducting cells, provide structural support)
phloem - tubes of cells, distribute sugars, amino acids, other org. prod
‣lignin = polymer that makes plants rigid, allowing them to grow tall
nonvas­cular plants
bryophytes lack vascular tissue
rhizoids - root-like anchor
gameto­phytes = larger, live longer than sporop­hytes
‣mature sporophyte fully depends on gameto­phyte for nutrition
‣limited to moist habitats
•liverworts
•mosses
•hornworts
seedless vascular
❋early vascular plants
sporop­hytes = large/more complex gen.
gameto­phyte & sporophyte are independent
‣sperm swims through water to egg (like bryophytes)
•lycop­hytes (club mosses)
•monilophytes (ferns)
seed plants
❋reduced gameto­phytes, ovules, pollen
seed= embryo + food supply + protective coat
•gymno­sperms = naked seeds
•angiosperms = enclosed seeds in ovaries
(flowers & fruits)

ALTERN­ATIONS OF GENERA­TIONS

gameto­phyte generation is haploid and produces haploid gametes by mitosis
fusion of sperm+egg creates diploid sphoro­phyte and produces haploid spores by meiosis

MULTIC­ELL­ULAR, DEPENDENT EMBRYOS

embryo within female gameto­phyte tissue, placental transfer cells ➝ nutrients
embryo­phytes —embryo dependent on parent plant

WALLED SPORES PRODCUED IN SPORANGIS

sporangia— multic­ellular organs that produce spores
sporop­ollenin (strong polymer) —in walls, resistant to harsh enviro­nments

OVULATE CONE

ovule= megaspore (haploid spore → female gameto­phyte) + protective layer(integ­ument)

POLLEN CONE

pollen grain = micros­pores (haploid spores → male gameto­phyte) + protective wall (w/ sporop­oll­enin)

**poll­ination - transfer of pollen to seed plant's ovules

EVOLUTION OF ROOTS & LEAVES

EVOLUTION OF ROOTS & LEAVES

FLOWERS & FRUITS

stamen = filament (stalk) + anther (sac produces pollen)
carpel = ovary (@ base) + style + stigma (where pollen is received)
ovary - 1/+ ovules

FUNGI

oldest fossils
460 million years ago, terres­trial
hetero­trophs that feed by absorption
FEED BY ABSORPTION secrete hydrolytic enzymes to break down complex molecules → small org. comp
chitin cell walls
divers­ifi­cation
•mold (multi­cel­lular)
•yeast (unice­llular)
life cycles & reprod­uction
‣most propagate by producing many spores, sexually or asexually
key role in land plant coloni­zation
symbiotic intera­cti­ons...
fungi/­other decomp­osers (fungi­/ba­cteria) break down dead organisms and return nutrients to physical enviro­nment

FUNGAL ADAPTA­TIONS TO LAND

SYMBIOTIC INTERA­CTIONS

mutualism
benefits BOTH

plant + fungi (endophytes) inside leaves­/other
•plant provide nutrition, some endophytes make toxins that deter herbiv­ore­s/p­ath­ogens
parasitism
benefits one, harms other

fungi absorb nutrients from host cells
lichen
photos­ynt­hetic microo­rganism(algae­/cy­ano­bac­teria)-fungus
•fungi benefit from carbs produced by algae/­cya­nob­acteria
•microorganism is protected by fungal filaments, gather moistu­re/­nut­rients
lichens break down surface & promote soil formation so plants can grow, on land 420 mya
mycorr­hizae
plant-­fungal — fungal hyphae transfer nutrients (phosp­hat­e/o­thers) to plant

earliest land plants lacked true roots/­leaves

MYCORR­HIZAE

THE RISE OF ANIMAL DIVERSITY

all animals (metazoa) share a common ancestor and likely evolve from multiple single­-celled eukaryotes (protist)

EUKARYOTIC SUPERG­ROUPS

sponges and choano­fla­gel­lates' (protists) simila­rities = animals evolved from choano­fla­gel­lat­e-like ancestor over 700 millions years ago

DIVERS­IFI­CATION OF ANIMALS

①all animals share a common ancestor
② sponges are sister group to ALL other animals
③eumatozoa = animals with tissues
④ most animal phyla belong to Bilaterian clade
⑤ most animals are invert­ebrates

EARLY-­DIV­ERGING ANIMAL GROUPS

sponges & cnidarians diverged from all other animals early on
sponges (PORIFERA)
basal animals
•lack true tissues
•filter feeders: capture small particles in water
water is drawn through pores into central cavity and flows out through an opening at the top

ANIMALS WITH TISSUES

eumeta­zoans
include cnidarians and all others
"true animal­s" = tissues
have symmet­rical bodies
(radial or bilateral)
•radial symmetry
cnidarians (jelly­fish, anemones)
- single, central axis
most animals are sessil­e{n­l}}➢2 embryonic tissue layers
→endoderm
→ectoderm
•bilateral symmetry
- 2 axes
animals that move actively
➢3 germ layers
→endoderm
→ectoderm
→mesoderm
cnidarians
tissues + radial symmetry, blind digestive system, carniv­ores, lack brain/­mus­cles, nerve net (simplest)
chordata
bilate­rians, verteb­rates, complete digestive tract
bilateral invert­ebrates
95% animals

EUMATOZOAN SYMMETRY

BODY CAVITIES

most bilate­rians posses a a body cavity (coelom)
- fluid/air filled space between digestive tract & outer body wall
 
cushions organs, acts as hydros­tatic skeleton, organs move indepe­ndently of body wall
 








 

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