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natural selection

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1

natural selection

A natural process resulting in the evolution of organisms best adapted to the environment.

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random evolution

mutation, genetic drift, and gene flow

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directional evolution

occurs when a certain allele has greater fitness than others, resulting in an increase of its frequency

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selective pressure

when the environment pushes an individual or population to adapt or evolve

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natural selection conditions

variation, heritability, differential reproductive success

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Evidence for natural selection

-Fossil record -Earth's age -Mechanism for heredity -Comparative anatomy

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artificial selection

Selection by humans for breeding of useful traits from the natural variation among different organisms

CRISPR

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Hardy-Weinberg equilibrium

condition in which a population's allele frequencies for a given trait do not change from generation to generation

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Population

A group of individuals that belong to the same species and live in the same area

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gene pool

Combined genetic information of all the members of a particular population

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allele frequency

Number of times that an allele occurs in a gene pool compared with the number of alleles in that pool for the same gene

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Allele

Different forms of a gene

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p

frequency of dominant allele

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q

frequency of recessive allele

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p+q=1

allele frequency equation

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16

BB

p^2

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Bb

2pq

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bb

q2

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p^2+2pq+q^2=

1 or 100%

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sample problem

Example: 2500 individuals in rabbit population, 900 have white fur Must know that white is recessive to black 900 out of 2500 are bb q2 = 900/2500 = 0.36 q = 0.6 and p = 0.4 (because p + q = 1)

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allele frequencies change due to...

small population size non-random mating mutations migrations selection

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Hardy-Weinberg equilibrium assumptions

  1. Large population

  2. No mutation

  3. No immigration or emigration

  4. Random mating

  5. No natural selection

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Breaking Assumptions

1)genetic drift randomly changes allele frequencies from generation to generation 2)inbreeding increases homozygosity non-random mates favor certain traits 3)mutations add genetic diversity 4)gene flow homogenizes distinct populations 5)selection can fix beneficial alleles, purge deleterious alleles, or maintain an appropriate balance between them

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genetic drift

random change in allele frequencies that occurs in small populations

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silent mutation

alters a base but does not change the amino acid

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nonsense mutation

changes a normal codon into a stop codon

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missense mutation

A base-pair substitution that results in a codon that codes for a different amino acid.

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Any violation of the conditions necessary for Hardy-Weinberg equilibrium can result in

changes in allele frequencies

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Speciation

Formation of new species

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species

A group of similar organisms that can breed and produce fertile offspring.

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Speciation concepts

members of populations that are able to interbreed -may not actually do so, but are capable of doing so -offspring must be viable and fertile

ability to interbreed is not necessarily based on similar morphology, but has a variety of underlying causes -relies on reproductive barriers

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reproductive barriers

factors that prevent different species from reproducing

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pre-zygotic barriers

A reproductive barrier that impedes mating between species or hinders fertilization if interspecific mating is attempted

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post zygotic barriers

reduced hybrid viability, reduced hybrid fertility, hybrid breakdown

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habitat isolation

populations live in different habitats and do not meet

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temporal isolation

form of reproductive isolation in which two populations reproduce at different times

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behavioral isolation

isolation between populations due to differences in courtship or mating behavior

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mechanical isolation

Morphological differences prevent fertilization.

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gametic isolation

Sperm of one species may not be able to fertilize eggs of another species

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reduced hybrid viability

When the genes of different species interact and impair hybrid development.

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reduced hybrid fertility

Sterile hybrids due to uneven chromosome number.

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hybird breakdown

hybrid offspring are born and fertile, but their offspring are weak and/or infertile

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allopatric speciation

The formation of new species in populations that are geographically isolated from one another.

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allopatric variance

non-overlapping habitats are formed by extrinsic events that split up a population

ex: lake drying up to form smaller lakes

results in isolated populations that diverge if the gene flow stops not all species are affected equally

-not all species are affected equally

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45

allopatric dispersal

when a few members of a species move to a new geographical area

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sympatric speciation

The formation of new species in populations that live in the same geographic area

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Sympatric sexual selection

habitats overlap, but a population gradually diverges into tow new species

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Sympatric habitat differentiation

habitats overlap, but a population gradually diverges into two new species

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Autopolyploidy

an individual that has more than two chromosome sets that are all derived from a single species

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Polyploidy

condition in which an organism has extra sets of chromosomes

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51

Biomes

A community of living organisms of a single major ecological region.

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Ecology

The study of how living things interact with each other and their environment

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organismal ecology

behavioral, physiological, and morphological ways individuals interact with environment

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population ecology

factors that affect population size & composition

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community ecology

interactions between species ecosystem ecology- energy flow between living and nonliving elements

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landscape ecology

study of multiple linked ecosystems

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global ecology

study of the biosphere- sum of all the planet's ecosystem

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How are biomes determined?

climate

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terrestrial biomes

classified by temperature and annual precipitation biomes determine

-fauna -flora -microbes -fungi

biomes are dynamic

  • respond to natural events

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tropical forests

-found closer to equator -tropic rain forest- high amounts of annual rainfall -tropical dry forest- seasonal precipitation -intense competition for light -more animal diversity than in any other terrestrial biome

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deserts

-temp varies seasonally and daily -precipitation is low but varies -vegetation is sparse -nocturnal animals -adaptations to survive water loss

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savanna

-equatorial and subequatorial regions -warm year round -low rain -grassland and trees -supports large herbivorous mammals -insects such as termites -fire is important in maintaining savanna biomes

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chaparrals

-high plant and animal diversity -organisms have adaptations to both fire and drought

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temperate grasslands

-seasonal variation in temp -deep fertile soils

-ideal for grain architecture -most grassland -deep fertile soils

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coniferous forests

-largest terrestrial biome on earth -home to birds and mammals -target for logging

-old growth forests disappear

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temperate broadleaf forests

-lots of precipitation -removed for cities -trees become dormant through winter -mammals hibernate and birds migrate

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tundra

covers large areas of the arctic -also found on high mountain tops at all latitudes

permanently frozen layer (permafrost) prevents root growth

migratory birds and mammals, though some large mammals stay year-round

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aquatic biomes

aquatic biomes are set by the presence of salt vs. fresh water

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photic zone

upper layer, receives enough light for photosynthesis

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benthic zone

bottom layer of sand & sediment

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abyssal zone

deep regions of open, water 2-6km deep

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Wetland Biome

-include marshes, bogs, & swamps -saturated or periodically flooded -one of the most productive biomes ex: home to diverse communities -many microorganisms producing & decomposing exs:water and soil have low dissolved O2 high capacity to filter dissolved nutrients and pollutants

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streams & rivers

-bodies of water that move in one direction -headwaters- cold, turbulent ex: -carry little sediment, mineral, nutrients -water picks up nutrients and oxygen as it travels downstream -nutrient content will be determined by terrain and vegitation

further from headwater- water movement slows, more nutrients picked up, path of travel becomes broad

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estuaries

-transition between river and sea -varies in salinity ex: daily fluctuations from tides -support many fish and invertebrate species -crucial feeding areas for many species of birds

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intertidal zones

-marine biome sometimes is submerged and exposed -upper intertidal zone exposed to air longer ex: greater variation in salinity and temperature -many organisms live only at a particular level of the intertidal zone ex: optimized for water, salinity, and temperature ranges

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oceanic pelagic biome

  • open blue water

  • covers 70% of earth surface

  • high oxygen levels, low nutrients level

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coral reef

-found in the photic zone of stable tropic marine environments -temp between 18-30c -reef formed by calcium carbonate skeletons of coral animals -vertebrates and invertebrates -reduction in reefs due to coral collection, overfishing, global warming

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marine benthic zone

-sea floor; receives no sunlight -organisms must adapt to continuous cold and extremely high pressure -unique communities arise around hydrothermal vents

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Biogeography

study of past and present distribution of individuals species

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80

biotic factors

living organisms in the environment

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81

abiotic factors

nonliving physical or chemical factors

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biotic factors

food availability predator herbivores for plants pollinators parasites/pathogens

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abiotic factors

temperature sunlight rainfall temperature nutrients soil conditions predation, parastisim, & competition (biotic) non-favorable environmental conditions (abiotic)

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sunlight is key for distribution

provides energy that drives nearly all ecosystems

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actual range

  • area where a species currently lives

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86

potential range

area where a species could live, even though it does not

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negative interactions

predation, parasitism, & competition (biotic) non-favorable environmental conditions (abiotic) <not enough water

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positive interactions

presence of food (biotic) & water (abiotic) symbiotic species (biotic) favorable conditions (abiotic) -ability to camouflage -correct temperature for physical traits

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population

A group of individuals that belong to the same species and live in the same area

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population characteristics- density

density results from processes that add or remove individuals

add birth migration remove death emigration (having to leave)

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population characteristics- dispersal

dispersion may be due to habitat preferences, social interaction, or other factors

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population characteristics- demographics

demography- study of vital stats in a population

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population growth

in an idealized population (with no immigration/ emigration):

ΔN/Δt= B-D

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n

change in population size

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t

time interval

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b

births

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d

deaths

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per capita birth rate

number of offspring produced per unit time by an avg member of the population

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per capita death rate

number of expected deaths per unit time in a population

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per capita rate of increase

r=b-d r>0= pop growth r<0= pop decline r=0= zero pop growth (steady)

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