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Diversity and
Evolution
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SC.912.L.15.10
SC.912.N.1.3
SC.912.N.2.1
SC.912.L.15.8
Evolution
Homozygous: both alleles are the same
Heterozygous: each allele is different
• Study of changes in populations, species,
or groups of species
• Occurs because populations VARY by the
frequency (number of) heritable traits
that appear from one generation to the
next
– Traits are represented by alleles
• Fancy word for a version of a specific
gene that controls a trait
– Ex. You have a gene for eye color….you
INHERIT different alleles for eye
color…blue alleles or brown alleles (you
get one from each parent)
• Evolution is…
– Changes in ALLELE frequencies in
populations over time
Two areas to study in evolution…
• Microevolution
•Macroevolution
Microevolution
• Describes the details of how populations of organisms change from generation to
generation
• Describes how a new species originates (speciation)
• Change in gene frequency in a population
• When evolution occurs quickly enough for scientists to observe
Examples:
• Bacteria
– Reproduce rapidly
– Trait for Resistance to antibiotics is passed down to offspring
– This is how bacteria become resistant to certain medicines…NOT GOOD
• Plants
– Resistance to herbicides
• Insects
– Resistance to pesticides
Macroevolution
• Patterns of evolution for groups of species over
extended periods of GEOLOGIC time
• Patterns determine PHYLOGENY
– The evolutionary relationships among species and groups of
species
• Remember our cladograms????
• 2 distinct macroevolution theories
– Phyletic gradualism
– Punctuated equilibrium
• Gradualism
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–
–
–
–
Two Ways MACROevolution is believed to
have Occurred
Evolution occurring over a long period of time
Slow and constant change
Small difference between generations
This is how Darwin believed NATURAL SELECTION worked
Evidence:
• Fossil records only provide snap shots of evolutionary process; reveals only
major changes in groups of organisms
• Incompleteness of our fossil record explains the absence of the intermediate
stages of development
• Punctuated Equilibrium
– Evolution occurs in spurts
– Causes:
• random mutations in DNA
• Sudden Major changes in environment
– Changes occur rapidly followed by long period without change
– Evidence:
• Fossil history consists of fossils of mostly extended periods of “stasis” (stability)
with few (if any) fossils from short, rapid bursts of evolution.
• Absence of fossils from intermediate stages of evolution confirms PUNCUATED
EQUILIBRIUM
MICROEVOLUTION
Describes details of how POPULATIONS of organisms change
from generation to generation and how NEW species originate
Species:
group of individuals capable of interbreeding and producing viable
offspring
Speciation:
formation of a new species
Before we get into speciation…
• Speciation is getting one group of species to split into
new, different groups
• This large group MUST become separated or
ISOLATED in some way so they can NO longer
interbreed…
• 7 types of isolation that can lead to speciation….
• Isolating Mechanisms
How to MAINTAIN reproductive
isolation
• Review: What is a ZYGOTE???
– Pre-zygotic isolating mechanisms (before a zygote is
even made)
• Ways to PREVENT fertilization
1.
2.
3.
4.
Habitat (geographical) isolation
Temporal isolation
Behavioral isolation
Reproductive Isolation
» Mechanical isolation
» Gametic isolation
– Post-zygotic isolating mechanisms (after zygote is made)
• Ways to prevent the formation of FERTILE offspring
5.
6.
7.
Hybrid inviability
Hybrid sterility
Hybrid breakdown
Pre-zygotic isolating
mechanisms (before a zygote is
even made)
1.
2.
3.
4.
Habitat isolation
•
Species A never Encounters species B
•
Species and mates/flowers at different time or season than
species B
Temporal isolation
Behavioral isolation
•
Species A doesn’t recognize species B’s mating ritual
•
Mechanical isolation
• Reproductive parts are incompatible
Gametic isolation
• Male gametes do not survive in the environment of the
female gamete
• Female gametes do not recognize male gametes
Reproductive Isolation
•
How We Get New Species
1.
Reproductive isolation
– When organisms of the same species become
genetically split and STOP breeding with each other
– Gene pool split, two different groups can no longer
interbreed
•
2.
3.
4.
Mechanical or gametic isolation
Behavioral isolation
– Groups of organisms of the same species develop
different courtship rituals (or behaviors) over time and
will not be attracted to others
Geographic isolation
– When two populations are separated by geographic
barriers
– Mountains, rivers, etc.
– Doesn't always separate all species…river and birds vs.
squirrels
Temporal isolation
– When two or more species reproduce at different times
– Specific day/season when that species is able reproduce
Post-zygotic isolating mechanisms
(after zygote is made)
5.
Hybrid inviability
• Zygote fails to develop properly
• Aborts or dies before reaching reproductive maturity (usually at
embryonic stage)
6.
7.
Hybrid sterility
• Hybrid becomes functional adult but they are reproductively sterile
• Eggs or sperm are non-existent or dysfunctional
Hybrid breakdown
• Hybrids produced actually DO produce offspring but their offspring have
reduced viability or fertility
• Microevolution:
Observed Evolutionary Change
– Describes details of how
POPULATIONS of organisms
change from generation to
generation and how NEW species
originate
– Species: group of individuals capable
of interbreeding and producing viable
offspring
– Speciation: formation of a new
species
3 processes of
speciation:
1.Allopatric Speciation
2.Sympatric Speciation
3.Adaptive Radiation
3 Processes of Speciation
1.
Allopatric Speciation
– Geographic barrier prevents
interbreeding between members
of the population
– Barrier leads to reproductive
isolation
– Allele frequencies change (due to
natural selection, genetic drift, or
mutation
– If gene pool changes too much,
interbreeding between
populations will no longer be
possible= NEW SPECIES
3 Processes of Speciation
2. Sympatric Speciation
– New species formed WITHOUT geographic barrier
– Due to:
• reproductive isolation
• Behavioral isolation
• Temporal isolation
Allopatric speciation
• speciation occurred in different regions
• Key: geographical separation
• Geographical isolation
Sympatric speciation
• one population of one species became two
species while in the same geographic region with
no physical separation
• (temporal isolation, reproductive isolation,
behavioral isolation)
3 Processes of Speciation
3. Adaptive Radiation
– Rapid evolution of MANY species
from a single, common ancestor
– Occurs when ancestral species is
introduced to an area where diverse
GEOGRAPHIC or ECOLOGICAL
conditions are available for
colonization
– Creates VARIANTS of ancestral
species that are SPECIALIZED for
particular environments
3. Adaptive Radiation
Adaptive Radiation
• Where species all deriving from
a common ancestor have over
time successfully adapted to
their environment via natural
selection
Niche
• Derived from Latin word
meaning “nest”
• The role an organism plays in its
community or ecosystem
• No two species can occupy the
same niche in the same area at
the same time
• Think of a sports
team…everyone has a specific
role on the field
– You can’t have two people
playing short stop at the same
time
Patterns of Evolution
Four Patterns Characterize the Evolution of Species
1.
2.
3.
4.
Divergent Evolution
Convergent Evolution
Parallel Evolution
Coevolution
• Organisms from the same
ancestor have developed
different
anatomies/behaviors (and
eventually form new
species)
• Environment influences
their new
anatomy/behaviors
1. Divergent
Evolution
2. Convergent evolution
• organisms that descended from different
ancestors
• Evolve similar anatomies and/ or
behaviors if they live in similar
environments
3. Parallel Evolution
• Two related species (from same lineage)
make similar evolutionary changes after
their DIVERGENCE from a common
ancestor
– Marsupial mammals and placental
mammals
– Independently evolved similar adaptations
when ancestors encountered similar
environments
4. Coevolution
• Evolution of one species in response to the evolutionary
adaptations made by another species
• Examples
– Predator and prey adaptations
– Plants and insect adaptations
– Pathogens and immune systems of animals
Summary of Evolution
• DNA is the blue-print for building ALL living things on planet Earth.
• DNA sequences are changed by:
•
•
•
•
•
•
•
random mutations
Radiation
Viruses
Chemicals
sexual reproduction
Migration
geological events
• As a result there is variation within populations of a species.
• Those individuals of a particular species with a phenotype (as a result of
their genotype) that is more fit to survive in a given environment has a better
chance to reproduce.
• Those individuals who reproduce more pass-on their genes at a higher
frequency than those who do not.
• EVERYTHING is trying to SURVIVE and REPRODUCE