Thurs./Fri. 5/12 – 5/13 Agenda

Thurs./Fri. 5/12 – 5/13Agenda1. 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 MaleBb 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 Selection2.Mutations3.Migrations4.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.