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Evolution
All the changes that have transformed
life from its earliest forms to what we
see today.
Evolution is the result of genetic changes that
occur in constantly changing environments.
Natural Selection
• Populations change in response to their
environment.
• Acts on phenotype of an organism.
(Not genotype)
Natural Selection
• Determines the
differential survival of
groups of organisms
Phenotype
• Observable
characteristics
(green eyes, brown
hair, purple flowers,
etc.)
Genotype
• Genetic makeup of an
organism determined
by a pair of alleles.
Allele
• Alternative form of a
gene for each variation
of a trait.
Gene
• Unit of hereditary
information
• Located on a
chromosome
• Contains DNA
Gene Pool
• Total genes in a
population at any one
time
Homozygous
• Having two identical
alleles for a trait
Heterozygous
• Having two different
alleles for a trait
Mutation
• Change in DNA of a
gene or chromosome
• Mutations occur
constantly in a gene
pool
Reproductive Isolation
• Prevention of mating
between formerly
interbreeding groups.
or
• The inability of these
groups to produce
fertile offspring
Geographic Isolation
• Physical barrier
divides a population
• These two groups are
not able to mate
=> may lead to new
species
Speciation
• Formation of a new
species
Mass Extinction
• An episode in which
many species suddenly
become extinct
Punctuated Equilibrium
• Evolutionary model
• Rapid changes to a
species in a short time,
followed by periods of
little change.
Gradualism
• Model of evolution
involving slow,
gradual changes to a
species over time.
Gradualism vs. Punctuated
Equilibrium
Bacteria
• First form of life on
Earth
• Evolved 3.5 billion
years ago
(prokaryotes)
• Eukaryotes (complex)
formed 1.5 billion yrs
ago
Multicellular life
• Evolved 570 Ma
(Cambrian explosion
of life!)
• Multicellular = more
than one cell
• Jellyfish-type
creatures were first
forms
•
Vertebrates
•
•
•
•
Have a backbone
1st were jawless fish
Amphibians 1st on land
Almost all land animals larger than a fist
Arthropods
•
• Have an exoskeleton
(Hard outer shell)
• First animals on land
(scorpion)
• Crabs, lobsters,
insects, spiders
Reptiles
• Evolved from
amphibians
• Diversified into many
forms after the
Permian mass
extinction (250 Ma).
•
Dinosaurs
•
•
• Evolved from reptiles and dominated the
Mesozoic Era
• Were wiped out by a large body that impacted
Earth 65 million yrs ago
Mammals
• Were very small
during the Mesozioc
• Became the dominant
life form after the
Cretaceous mass
extinction (65 Ma)
•