Download Types of Natural Selection

TYPES OF
NATURAL
SELECTION
DEFINITIONS..
• Evolution is the change in a
population’s genetic material
(alleles) over generations.
DEFINITIONS..
• Evolution is the change in a
population’s genetic material
(alleles) over generations.
• A population is in genetic
equilibrium if it’s not evolving
DEFINITIONS..
•
Evolution is the change in a
population’s genetic material
(alleles) over generations.
•
A population is in genetic
equilibrium if it’s not evolving.
•
If the population’s allele
frequencies stay the same year to
year then it’s not evolving.
HARDY-WEINBERG GENETIC
EQUILIBRIUM
• Hardy-Weinberg equilibrium describes
populations that are not evolving
HARDY-WEINBERG GENETIC
EQUILIBRIUM
• Hardy-Weinberg equilibrium describes
populations that are not evolving
• Genotype frequencies stay the same
over time as long as certain conditions
are met:
HARDY-WEINBERG GENETIC
EQUILIBRIUM
• Hardy-Weinberg equilibrium describes
populations that are not evolving
• Genotype frequencies stay the same
over time as long as certain conditions
are met:
• Very large populations
• No emigration or immigration
• No mutations
• Random mating
• No natural selection
NATURAL SELECTION (3 TYPES)
•
Organisms best suited to their environment live
to reproduce and pass on their genes
•
Acts on a phenotype
•
Varying types of selection
1. DIRECTIONAL
SELECTION
• Individuals with a more extreme form of trait
have higher fitness
Normal Distribution
Distribution after Selection
Suppose termites in
an area begin to
build deeper nests.
Anteaters with long
tongues could more
effectively prey on
termites than those
with short or
average tongue
length
2. STABILIZING
SELECTION
•
Having average form of trait has highest
fitness
Blue curve shoes
variation after a new
predator is
introduced. Predator
can easilty capture
the large, visible
lizards and the small
slower lizards. Thus,
selection against
these extremes
body types reduces
the size range in
lizards
Normal Distribution
Distribution after Selection
3. DISRUPTIVE
SELECTION
• Individuals with any extreme trait has a higher
fitness and most likely results in two new
species
• Divergent Evolution
The white limpets
blend in with
barnacles on rocks.
On bare rocks, darkshelled limpets
blend in. However,
the tan colored
limpets are easy to
spot by birds.
Normal Distribution
Distribution after Selection