Download Natural Selection

Mechanisms of
Evolution
Population Genetics and Evolution
Can Individuals Evolve?
Natural Selection acts on the range
of individuals in a population.
Evolution occurs as a
populations genes change over
time.
The
Gene Pool
Gene pool: all of a population’s
genes
% of a specific allele in the gene
pool is the frequency.
If the frequency is staying the
same, we call that pool in genetic
equilibrium.
Practice
Population of this room ( )
Number of people with mid
digit hair
( ) HH
%-
( ) Hh
%-
Number without
( ) hh
%-
Changes in Genetic Equilibrium
Mechanisms for Change in Genes
Mutation
Genetic Drift
Natural Selection
Stabilizing
Directional
Disruptive
Mutation
Most are harmful
organisms don’t survive,
hence gene is eliminated
Rare few are useful
natural selection,
becomes part of gene
pool
Genetic Drift
Alteration of allelic frequencies by chance
events.
Small population of individuals
natural disaster (bottleneck effect)
founder’s effect
isolation
Genetic Drift - genes added and lost from
the pool
Natural Selection
Most common source of
genetic change
Some genes help ( or
hinder) organisms
survival
Different Types
Stabilizing Selection
Favors average individuals in a
population
Average size have an
advantage and are ‘selected
for’
Ex. Birth weight
too small - health problems
too large - delivery
complications
Directional Selection
Nature favors one of the extreme
variations of the trait.
Trait on the extremes are an
advantage so they are
‘selected for’.
Ex. Cheetah’s Speed
Slow - not feed
Fast- eat better
Disruptive Selection
Individuals on both
extremes are selected.
Ex. Darwin’s finches
extremes were an
advantage for
certain types of food
Sexual Selection
Sex (typically females)
select mate based on
certain traits
Natural Selection from
mating
Speciation
A species is a population
whose members can breed
and produce fertile
offspring
Speciation is when a new
species is formed
Speciation Isolations
Speciation occurs because the species is isolated and
changes happen until the species no longer interbreeds
Reproductive Isolation (3 ways)
Geographic Isolation
Behavioral isolation
Temporal Isolation
Geographic Isolation
islands, rivers, bodies of water, mountains
Behavioral Isolation
Different mating songs, mating rituals
Temporal Isolation
different mating seasons