Download Evolution Notes Part 2 - Mercer Island School District

Gene Pool- _______________
____________________
Prerequisites
Process
Individuals with
favorable traits
Variation for trait are more likely
to survive/
reproduce &
Traits causes
pass down these
differences in
__________ and favorable genes.
reproduction.
Trait is heritable
Outcome
A change in the
__________with
the favorable
genes becoming
more common.
Adaptation for
the environment.
Normal Distribution
A normal distribution is one that forms a _____________
______________. (Variation in trait on the X axis, number
of individuals on the Y axis)
Example: Height in females: Average height is 5’4’’
Types of Natural Selection
Directional selection:
 Favors individuals with traits that are at ___________
of a distribution.
 Results in the distribution __________ , with an
increase in the favorable form.
Types of Natural Selection
Stabilizing selection:
 Eliminates individuals at _________of the spectrum.
 Results in a ___________distribution ; the average
remains the same.
Types of Natural Selection
Disruptive selection:
 Eliminates average individuals, but favors individuals
at either extreme of the spectrum of variation.
 Results in a __________ distribution, with fewer of
the average form and more of the extremes.
© Brooks/Cole Publishing Company / ITP
Discuss with your table
partner:
On the next four slides are examples of different
types of natural selection. Determine the type
of selection (directional, diversifying or
stabilizing) for each example. Also, describe
how the distribution graph would change over
time.
On an island, prickly pear cacti with the lowest
branches are more likely to be eaten by iguanas.
Which kind of selection is this and how could
the distribution of prickly pear branch height
change?
__________selection; could result in ______
prickly pear trunks.
Chimpanzee babies are more likely to survive
birth if they are not too large or too small.
Which kind of selection is this and how could this
change the distribution?
_________ selection; could result in a
________distribution of birth size.
On an island, dragonflies with longer wings are
more likely to get blown out to sea. Which type
of selection is this, and how could it change the
distribution of wing length.
_________ selection; could result in the average
wing length _____________.
A species of begonia on average flowers in
August. Its pollinators become less active in
August due to the heat.
Which type of selection is this, and how could
the distribution change?
__________ selection; could result in fewer
plants that flower in ___________________
_________________.
Genetic Equilibrium: If the percentage of different
genes for a trait __________________ , than the trait
is in genetic equilibrium.
Time