Evolution: Natural Selection and Phenotypes
Big Idea 1: Process of evolution
drives the diversity of life
Essential Knowledge
• 1A1: Natural selection is a major mechanism of
evolution.
• 1A2: Natural selection acts on phenotypic
variations.
• 1A3: Evolutionary change is also driven by
random processes
Evolution
• Change in genetic makeup of a population over
time.
• Natural selection is its major driving mechanism.
What do
you
know
about
this guy?
Darwin said…
What’s
wrong with
this picture
though???
• Competition for limited resources
results in differential survival.
Natural Selection
• Individs w/ more favorable phentoypes
(physical features) are more likely to survive
and produce more offspring, passing down
traits to subsequent generations!
Describe
Pandy’s
phenotype
Genetic Code:
DNA/RNA
Physical features
and Behaviors
Types of Natural Selection
1) Stabilizing
Selection:
Selective
pressures select
against the 2
extremes of a trait.
• Ex: Better to be
average!
Types of Natural Selection
2) Directional
selection: 1
extreme of the
trait experiences
selection against
it.
• Ex: giraffes w/
short necks
Types of Natural Selection
3) Disruptive
selection: Selection
pressures act
against individuals in
middle of 2 extremes
of the trait.
• Ex: Don’t be
average
Evolutionary Fitness
• To be fit, you must be able to reproduce!
• Measured by reproductive success.
Why is the Zorse Not Evolutionary Fit?
Genetic Variation is Good For You!
• A diverse gene pool is important for
survival of a species in a changing
environment.
Adaptation
• A genetic variation that is favored by selection and
provides an advantage to an org. in a
environment.
• Occurs naturally through environmental
pressures.
• Chance and random events (genetic drift)
can also influence the evolutionary
process, especially for small pops.
What is Going to Happen to this Small
Population, thanks to Genetic Drift?
Natural Selection Acts on Phenotype
• Environments may change and act as a
selective mechanism on populations.
Peppered Moth Video Clip
If the environment changes, different genetic
variations can be selected in each generation.
Global warming and earlier flowering
time
Phenotypic variations occur b/c of random
changes (mutations) and new gene
combinations (fertilization and meiosis)
Some Phenotypic Variations Increase Fitness
• Ex: Sickle cell anemia (Ss) makes you far less
likely to die from malaria. Heterozygote
advantage.
Whose
fitness will
be
decreased?
Humans Impact Variation
• Often times decreasing it…food crops
have been artificially selected to be
genetically similar.
Wooly Worm Lab
• Natural Selection and Chi Square Test!