Download Evolution Notes 2

Understanding
Evolution in terms of
Genetics
DARWIN’S UNDERSTANDING VS. PRESENT DAY
How are inheritable traits passed?
How do variations appear?
Today’s understanding of genes, DNA, variation,
and mutations is central to our understanding of
how evolution works
MICROEVOLUTION
• Mutations & Gene shuffling
• Natural selection of traits
• Single gene traits
• Polygenic traits
• Genetic drift
• Gene flow
Smaller Picture
MACROEVOLUTION
Mutations
Natural selection + 3.8 billion years = Macroevolution
Genetic Drift
Gene flow
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Adaptive radiation
Convergent & divergent evolution
Coevolution
Gradualism
Punctuated equilibrium
Mass extinction
Bigger Picture
POPULATIONS AND GENE POOLS
Population: group of the same species that interbreed
Gene pool: consists of all genes, including all the
different alleles, that are present in a population
Large gene pool
High genetic
diversity
Increased chances
of biological
fitness & survival
Small gene pool
Low genetic
diversity
Decreased
chances of
biological fitness
& extinction
Microevolution – Mutations & Gene Shuffling
Mutations
 Not all mutations are harmful
 Some mutations can actually be beneficial &
increase organism’s fitness
Gene Shuffling
 Gene shuffling will produce different phenotypes
 No change the relative frequency of alleles in the
populations
Microevolution – Natural selection of Traits
Single Gene Traits
Polygenic traits
 Controlled by a single gene that has two
 Controlled by two or more genes
 Polygenic traits have many possible genotypes
alleles
 Variation only leads to two possible
and phenotypes
 Represented with a bell shaped or “normal
phenotypes
 Represented with a bar graph
Ear lobe attached
distribution” curve
Ear lobe detached
Effect of Natural selection on
Single Gene traits
Natural
selection
Changes in allele
frequencies
Evolution
Effect of Natural selection on polygenic traits
Directional selection
 A single phenotype is favored
 Due to environmental changes
Stabilizing selection
 An intermediate phenotype is
favored
 More homogenous population
Disruptive selection
 Often extreme phenotypes are
favored
Main driving force behind speciation
Microevolution – Genetic Drift
Genetic drift: Large changes in allele frequencies due to a random event
Small gene pool
Low genetic diversity
FOUNDER EFFECT
BOTTLE NECK EFFECT
Decreased chances of biological fitness &
extinction
FOUNDER EFFECT
BOTTLENECK EFFCT
Microevolution – Gene flow
Speciation
 Behavioral Isolation: Differences in traits or habits
Speciation
 Geographical Isolation: Land separation of individuals
Speciation
 Temporal Isolation: Mating season is different
Evolution of Darwin’s Finches
2
1
4
3
5
Macroevolution Patterns
Adaptive radiation
Habitat & Niche
 Habitat: It is the place where an
organism lives (Where do you live?)
 Niche: The niche refers to the role of the
organism in the system (What do you
do?)
Convergent Evolution
Penguin
Bird
No common
ancestor
Seal
Mammal
Divergent Evolution
Polar Bear
Brown Bear
common
ancestor
Macroevolution Patterns
Coevolution
Macroevolution Patterns
Gradualism
Punctuated equilibrium
Macroevolution Patterns
Cretaceous-Tertiary mass
extinction (aka- K/T extinction)
Wipe out of Dinosaurs
Triassic-Jurassic mass
extinction
Many marine reptile, amphibians were lost
Permian mass extinction (aka
Great Dying)
96% of species died. All life on Earth today
is descended from the 4% of species that
survived
Late Devonian mass
extinction
Three quarters of all species on Earth
died out
Ordovician-Silurian mass
extinction
Lots of sea creatures were lost
Macroevolution Patterns
Convergent Evolution
Divergent Evolution