Selection
What is evolution?
What is evolution?
change in the allele frequency of a population over time
What are the 5 ways allele frequencies can change?
What are the 5 ways allele frequencies can change?
Genetic drift (small population size)
Sexual selection or non-random mating
Mutation
Gene flow or gene migration
Natural selection (survival of the fittest)
Natural Selection vs Artificial Selection
Artificial Selection → selective breeding of plants and animals to promote the
occurrence of desirable traits in offspring.
● Apples video
● Foxes video
● Natural vs Artificial video
Selection on single-gene traits
One allele offers higher fitness than the other.
One phenotype becomes more common than the other.
Selection on polygenic traits
1. Directional (one extreme
is advantageous)
more peccaries, more spines
Selection on polygenic traits
2. Stabilizing (tweeners have the
advantage)
Selection on polygenic traits
3. Disruptive (both extremes are favored)
Practice Problem
Human babies with an average mass are more
likely to survive than babies born much smaller or
much larger than average.
Use a picture and words to describe which type
of selection may occur in baby mass over time.
Practice Problem
A seed-eating Galapagos Finch population
experiences a shortage of small seeds.
Use a picture and words to describe which type
of selection may occur in beak size over time.
Practice Problem
A seed-eating Galapagos Finch population
experiences a shortage of medium-sized
seeds.
Use a picture and words to describe which
type of selection may occur in beak size over
time.
Practice Problem
Which type of selection
is being shown in this
diagram? Why might
this be occurring?
Practice Problem
Which type of selection lead to giraffes
with long necks? Use a picture to explain
your answer.
Practice Problem
Which type of
selection is influencing
rabbit leg length in this
scenario?
Genetic Equilibrium
● Genetic Equilibrium: Allele frequencies do
not change over time = no evolution
B relative
frequency
.6
.6
.6
.6
.6
b relative
frequency
.4
.4
.4
.4
.4
What would cause genetic equilibrium? Think: It is the opposite of evolution.
Breeding Bunnies Activity