Download Types of Natural Selection

TYPES OF
NATURAL
SELECTION
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
• 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
EXAMPLE
Suppose a new predator is released into the environment.
Large fish are stronger swimmers and can get away. Draw a
new curve showing what the histogram will look like after 200
years.
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
•
Reduces extremes
3. DISRUPTIVE SELECTION
• Individuals with either extreme trait has a
higher fitness and most likely results in two
new species
EXAMPLE
Suppose a new predator is released into the environment.
Large fish are strong swimmers and can get away from
predator. Small fish can hid in the cracks and crevices of the
rocks. Draw a new curve showing what the histogram will
look like after 200 years.