Thurs./Fri. 5/12 – 5/13
Agenda
1. Ch. 32 PPT Sec. 2-3
– Student notes
2. Evolution Online Activity
– Worksheet/Game
3. Diversity/Evolution Reading
– Answer ? 1-11, 22-34, 36
4. Ch 32 Vocab./Word Search
Objectives
• Write notes in advanced organizer
– Identify and explain 4 factors that cause changes in
the gene pool
– Explain how isolation influences evolution
– Describe 2 theories that explain the rate of
evolution
• Answer ? From the Diversity/Evolution Reading
• Play the online Evolution game and write in
their answers on the WKST
• Define Key terms
Chapter 32 Theories of Evolution
Discovery education Video
Show video!
Evolution & Genetics
• Darwin could not explain the causes of variations,
or how they were passed on to offspring.
• Why do you think Darwin could not explain the
causes of variations?
– Discoveries in the field of genetics have not been
made yet! He did not know about gene mutations!
Evolution & Genetics cont.
• Today, scientists studying evolution examine
variations in a population.
• What is a population?
– All the members of the same species that live in the
same area
– Ex: cattle on a farm, tilapia in a stream, Hawaiian
Honey Creepers in Waimea Valley
Evolution & Genetics cont.
• To understand how populations change, scientists
look at the kinds and # of genes in a population.
• All the genes in a population make up the gene
pool which is a collection of all the genes for all
the traits in a population.
Evolution & Genetics cont.
• This gene pool goes
back to what we
learned about when we
did Punnett squares.
• Ex: Brown skin is
dominant to white skin
in wild boars.
Determine the
genotype and
phenotype ratio for a
heterozygous female
and a heterozygous
male.
Brown= B
White = b
Female
Bb
Male
Bb
B
b
B
BB
Bb
b
Bb
bb
Genotype
Phenotype
25% Homo. dom.
75% Brown
50% Hetero.
25% White
25% Homo. Rec.
Evolution & Genetics cont.
• Evolution can only occur when there is a
change in the kinds or % of genes in the gene
pool of a population.
• What causes changes in the gene pool?
1. Natural Selection
2. Mutations
3. Migrations
4. Isolation
Natural Selection
• Natural selection allows organisms that are well
adapted to their environment survive and
reproduce.
• Other less fit organisms have a lower chance of
surviving and reproducing.
• Therefore, well-adapted organisms pass on more
of their genes to the next generation.
• As a result the gene frequency changes from one
generation to the next.
Peppered Moth Example!
Mutations
• Mutation is a change in the structure of a
gene or chromosome
• It adds a new gene to the gene pool.
• Because mutations are normally recessive it
may remain in the gene pool for many
generations without changing the appearance
of the population.
• Mutations can be helpful or harmful!
• Some mutation are neither helpful nor
harmful
Mutations
Migrations
• Migration is the movement of members of a
species into and out of a population.
Isolation
• Sometimes, a group of
organisms may become
isolated from other
members of its
population.
• Geographic isolation:
when physical barriers
separate 2 populations.
– Ex: Rivers, mountains,
different islands.
Isolation cont.
• Geographic isolation often results in speciation,
or the development of a new species.
Isolation cont.
• Geographic isolation  reproductive isolation.
• Even if the physical barrier is removed organisms
from different populations can no longer mate
and produce offspring.
• Leads to a new species.
Rate of Evolution
• Most scientists support Darwin’s theory of
evolution by natural selection.
• Not all agree on how long it takes
• Like Darwin’s most scientists believe that
evolution is a slow process in which species
change gradually over long periods of time
(gradualism).
Rate of Evolution cont.
Rate of Evolution cont.
• Some other scientists have proposed that
evolution occurs mostly in a series of rapid
changes.
• In 1972, a theory called punctuated equilibrium
was proposed.
• Punctuated equilibrium: theory that species
remain the same for millions of years, then,
within a short period of time, certain species
suddenly die off while other species suddenly
appear.