Download Natural Selection & Phenotype

Natural Selection & Phenotype
I will understand how natural selection
acts on the phenotype rather the
genotype of an organism.
MT: Allele frequency
Review of Phenotype
Phenotype = physical
traits of an organism
Expression of
genotype
Salamander's P'type:
Orange, 4 limbs, 1
tail, 2 dark eyes,
smooth, spots on
posterior side
Review of Phenotype
Describe this fox's
phenotype?
Describe this fox's
fitness.
More practice...
What is an adult
penguin's phenotype?
Does an adult
penguin or a chick
have better fitness?
Defend your answer.
Phenotype & Natural Selection

Compare box 1, 2, & 3. Which mouse is has a
higher survival rate? Why?
Types of Natural Selection
1. Directional
Selection
2. Stabilizing
Selection
3. Disruptive
Selection
1. Directional Selection
•
Environment favors
individuals with
phenotype at one
extreme
•
Ex: 1. Giraffe neck
Longer necks have better
chance of surviving and
reproducing so over time
the whole species has a
longer neck
1. Directional Selection
•
Favors
phenotype at
one extreme
•
Over time the
whole
population
starts having
the phenotype
of one extreme
2. Stabilizing Selection
•
Environment favors
phenotype that is
average (most common)
•
Ex: human baby size
at birth
(7-9 lbs is best)
Big babies have difficult time
coming out.
Small babies have difficult time
surviving.
2. Stabilizing Selection
•
Favors
average
phenotype
•
Over time,
majority of
individuals are
average
3. Disruptive Selection
•
Environment
favors
phenotypes at
both extremes
•
Ex: Darwin's
finches
Some islands did not have the
food needed for mid size
beaks so small and large
beaks were favored
because they could find
food
3. Disruptive Selection
•
Favors
phenotypes of
both extremes
•
Over time, can
lead to
speciation
Critical Question:

How are natural selection and
phenotype connected?
Answer:
In nature, those
who are best fit,
have the best
phenotype, thus
have a higher
chance of surviving
and reproducing.
So, natural
selection directly
acts on an
organism's
phenotype.
Planet Earth clip
http://www.youtube.com/watch?v=A0E6geAq1k8
1.What was the phenotype of the wolf that was
successful?
2. What type of selection (directional, stabilizing,
or disruptive) most likely acted on the caribou's fur
color?