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 |
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mutation (change in nucleotide sequence) |
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point mutations (single nucleotide change) ex. sickle-cell |
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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 |
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 |
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population -gene flow interrupted→ subpopulation |
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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 |
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reproductive barrier, reduced gene flow |
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polyploidy, habitat differentiation, sexual selection |
polyploidy |
extra chromosomes |
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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 |
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geographical |
physical barrier (rivers, mountains) |
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habitat/ecological |
same area, diff habitats |
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temporal |
diff breeding times |
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behavioral |
unique courtship rituals |
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mechanical |
morphological diff |
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gametic |
cannot fertilize |
Postzygotic Barriers |
prevent a viable, fertile hybrid |
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reduced hybrid viability |
poor development/survival |
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reduced hybrid fertility |
fertile hybrid |
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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
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
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 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 |
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evolution of novel characteristics |
ex. rise of photosynthetic organisms |
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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 |
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heterotroph = consumers |
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parasites = |
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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 |
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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
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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
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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
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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 cyanobacteria ➟ green algae ➟ land plants
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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)
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 |
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 |
BODY CAVITIES
most bilaterians posses a a body cavity (coelom) |
- fluid/air filled space between digestive tract & outer body wall |
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cushions organs, acts as hydrostatic skeleton, organs move independently of body wall |
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