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BIOLOGY | Evolution
MICROevolution change from generation to generation / form new
species
MACROevolution patterns of change in groups (related species)
over broad periods of time
- Phyletic Gradualism evolution occurs by gradual accumulation
of small changes- Punctuated Equilibrium evo history consists of
geo long periods of stasis with little/no evolution
rapid, punctuated evolutionary events
LAMARCK theory inheritance of acquired characteristics
DARWIN theory Natural selection / Survival of the fittest
Natural Selection
1. Large reproductive potential2. Pop sizes stable3. Resources
limited4. Competition to survive
5. Variation among individuals6. Much variation is heritable
(DNA)7. Most fit survive8. Favored traits accumulate in pop
Kinds of Selection
1. STABILIZING selection most common traits best adapted2.
DIRECTIONAL selection favors traits at one extreme
a. Peppered moth3. DISRUPTIVE/DIVERSIFYING selection environment
favors extreme traits
a. Short weeds on lawns escape mowing / tall weeds in wild get
more sunlight4. SEXUAL selection differential mating of males in
pop.
a. Females increase fitness by increasing quality of offspring
by choosing superior maleb. Males increase fitness by maximizing
quantity of offspring producedc. Sexual dimorphism diff in
appearance = form of disruptive/diversifying selection
5. ARTIFICIAL selection breeding animals/plants that possess
desirable traitsa. Form of directional selection (favors one
extreme)
Sources of Variation
- SEXo Crossing over Prophase 1 meiosis exchange of DNA btw
nonsister chromatids of
homologous chromosomes
o Independent assortment -- Metaphase 1 result = daughter cells
with random combo ofmom & dad chromosomes
- DIPLOIDY has 2 copies of each chromosome in cello Rr -- diff
alleles for single gene locus are present; r is hidden and stored
for future gens
- OUTBREEDING mating with unrelated partner- BALANCED
POLYMORPHISM maintenance of different phenotypes in pop
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BIOLOGY | Evolution
o Heterozygous advantage greater selective advantage than either
homozygous conditiono Hybrid vigor superior quality of offspring
from cross of 2 different inbred strains
Results from reduction of loci with deleterious rr conditions
and increase in loci withRr advantage
o Frequency-dependent Selection (minority advantage) when least
common phenotypehave selective advantage
**Not all variation has selective value NEUTRAL VARIATION
Allele Frequency Changes
- NATURAL SELECTION- MUTATIONS- GENE FLOW introduction/removal
of alleles- GENETIC DRIFT random increase or decrease of
alleles
o Founder Effect allele freq of migrating individuals are not
same as pop origin Amish with polydactylism
o Bottleneck dramatic decrease in size (natural catastrophe,
predation, disease, etc.)- NONRANDOM MATING
o Inbreeding and/or sexual selection
GENETIC EQUILIBRIUM: Hardy-Weinburg Equilibrium
p dominant allele frequency
qrecessive allele frequency
p2, q2 frequency of homozygotes
p2+ 2pq + q2frequency of heterozygotes
p + q = 1 (all alleles sum to 100%)
p2+ 2pq + q2=1 (all individuals sum to 100%)
SPECIES capable of inbreeding
SPECIATION formation of new species
Types of Speciation
1. ALLOPATRIC pop divided geographically so that interbreeding
btw 2 resulting pop is prevented
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BIOLOGY | Evolution
2. SYMPATRIC form new species w/o geo barrier presenta. Balanced
polymorphism insects of same color mate bc other ones did not
camouflage well
and were eaten
b. Polyploidy possess more than normal 2 sets of chromosomes
found in 2n cellsi. Often occurs in plants
c. Hybridization 2 distinct forms of species mate and produce
progeny along hybrid zonebarrier
3. ADAPTIVE RADIATION relatively rapid evolution of many species
from single ancestor due todiverse geo/eco conditions available for
colonization
Maintaining Reproductive Isolation
- PREzygotic Isolating Mechanismso Habitat isolationo Temporalo
Behavioralo Mechanicalo Gametic
- POSTzygotic Isolating Mechanismo Hybrid Inviability when
zygote fails to develop properly and aborts/dies prematurelyo
Hybrid sterility functional adults, but cannot reproduce
(eggs/sperm sterile or
dysfunctional)
o Hybrid breakdown hybrids produce offspring with reduced
viability/fertility
Patterns of Evolution
- DIVERGENT common ancestor- CONVERGENT 2 unrelated species with
similar traits (analogous traits)- PARALLEL 2 related
species/lineages with similar evolutionary changes- COEVOLUTION
tit-for-tat evolution of 1 species in response to new adaptations
in another species
(predator and prey / pathogens and immune systems)
