Objective: SWBAT describe natural selection.

Catalyst: What is variation? What causes variation?

What is one cause of mutations?

What is fitness?

Natural Selection

Write in complete sentences!

Don’t talk during the Catalyst!

HW review

Questions???

Mutations Review

Mutations occur all the time. They can either INCREASE FITNESS, DECREASE FITNESS, or NOT CHANGE FITNESS. An example of a mutation that increases fitness:

A cheetah got a mutation that made their legs a little longer and they can run faster. WHY???

An example of a mutation that decreases fitness:A bird had a mutation that made them call at a sound frequency that predators can hear easily. WHY???

An example of a mutation that has no effect:A codon that was supposed to be translated CAA gets translated as CAG. They both still produce glutamine. WHY???

The ENVIRONMENT matters!

The environment determines whether or not a mutation is good.

Having extra fur might be helpful in the north pole… but it would not be helpful in the desert. WHY???

NOT GOOD BECAUSE OF THE ENVIRONMENT.

So mutations cause variations in a population… say crickets! Population: A group of organisms of the same species that live in the same environment

There are just all these different crickets hanging out until…

Key Point #1: When an environmental pressure arises, certain traits will be “selected” for.

Putting it together…

Environmental Pressures

Examples: In a population of lions, a shortage of prey can cause certain types of lions to be selected for… What is the environmental pressure? What kind of lions would be selected for?

In a population of peacocks, a shortage of mates can cause certain types of peacocks to be selected for… What is the environmental pressure? What kind of peacocks would be selected for?

So what?

What happens to mutations that decrease fitness?

What happens to mutations that increase fitness?

Natural Selection

Key Point #2: Natural selection is the process by which mutations that increase fitness become more common over time, and mutations that decrease fitness become less common over time.

“Common” where? The gene pool is all the genes in a population of an organism.

Natural Selection

Good mutations are “selected for” (kept around) by natural selection A good mutation gives an organism an advantage that lets it produce more offspring.

Many organisms will be born with the mutation, and it will become more common in the gene pool.

REALLY IMPORTANT!!! Make sure to get this down IN YOUR OWN WORDS!!!

Natural Selection

Bad mutations are “selected against” (weeded out) by natural selection A bad mutation gives an organism a disadvantage that causes it to produce fewer offspring.

Few organisms will be born with the mutation, and it will become less common in the gene pool.

REALLY IMPORTANT!!! Make sure to get this down IN YOUR OWN WORDS!!!

Environmental effect

AWESOME NATURAL SELECTION DEMO

Guided Practice 1

Koalas have hands and feet that allow them to have a vice grip on tree branches. What caused this trait? Does this increase or decrease fitness? Why?

What about the environment makes it beneficial?

What will happen to this trait in the gene pool?

In what environment would this trait not be helpful?

Guided Practice 2

Wolves developed thick fur in the desert. What caused this trait? Does this increase or decrease fitness? Why?

What about this environment makes it harmful?

What will happen to this trait in the gene pool?

In what environment would this trait be helpful?

Let’s Model Natural Selection To model how natural selection occurs, we will do a crackers lab!

Remember: It is the ENVIRONMENT that determines if a mutation is good!!!

Key Point Wrap-Up

Key Point #1: When an environmental pressure arises, certain traits will be “selected” for.

Key Point #2: Natural selection is the process by which mutations that increase fitness become more common over time, and mutations that decrease fitness become less common over time.

Exit Questions

What determines if an mutation is good or bad?

Describe natural selection. Tricky! Give an example of a good mutation of any animal. Look back at this tomorrow and see if it still holds true.

Write in complete sentences!

Don’t talk during the Exit Question!