Lesson 6 – Mechanisms of Evolution:

What forces drive the changes in a population?

Evolution

What forces drive the changes in a population?

Objectives:– Identify the mechanism that aid in the coarse of

evolution.– Explain how the mechanism of evolution work.– Define the terms:

Mutations, Migration, Genetic Drift, Natural Selection.

What forces drive the changes in a population?

Evolution is responsible for both the remarkable similarities we see across all life and the amazing diversity of that life.

The basics of changes and similarities among individuals in a population is due to– Genetic Variation.

How does it work?

These changes (in genetic variation) can be caused by:

1) Mutations:2) Migration:

3) Genetic Drift:4) Natural Selection:

– All of these ‘mechanisms’ can change the frequencies of genes (how many times it can be found) in populations, and so all of them are called mechanisms of evolutionary change.

What forces drive the changes in a population?

*Biology-Online Definitions

Lets see how these mechanisms change a population and thus evolution.

1) Mutations: “A permanent, heritable change in the nucleotide

sequence in a gene or a chromosome; the process in which such a change occurs in a gene or in a

chromosome”*

Examples of these mutations are:– Mimicry and Camouflage,

What forces drive the changes in a population?

* Biology Online Definitions

Some kinds of adaptations:

Mimicry– “The resemblance which certain animals and

plants exhibit to other animals and plants or to the natural objects among which they live, a characteristic which serves as their chief means of protection against enemies”*

– Do you understand what they meant? If you didn’t , don’t worry. Lets take a look.

Mimicry:• These two butterflies look very much alike, but

they belong to different species.

• One of these butterflies is unpalatable (tastes bad) to predators. Can you figure out which one?

What forces drive the changes in a population?

A B

This frog is harmless

These two are deadly

Another example of mimicry:

What forces drive the changes in a population?

One of these frogs is harmless. Can you tell

which one?

Another example of mimicry:

These insects look like bees

• But they are not!

They are flies and they are harmless.

• Why would they need to look like bees?

What forces drive the changes in a population?

Camouflage:– Structural adaptation that enables species to

blend with their surroudings; allows a species to avoid detection by predators

– Did you understand what they meant?

If you didn’t , don’t worry. Lets take a look.

What forces drive the changes in a population?

What forces drive the changes in a population?

An example of camouflage:

Now, can you tell me what is meant by camouflage?

More examples of camouflage:

What forces drive the changes in a population?

An example of camouflage:What forces drive the changes in a population?

Can you tell what animal it is?

Come on, look hard……

I’ll give you a hint….

Is a Frog!

An example of camouflage:

What forces drive the changes in a population?

Can you see this one?

Is a walking stick

Organisms that demonstrate one of these types of mutations, will help it survive and thus pass these genes onto the next generation.

What forces drive the changes in a population?

2) MIGRATION:– The periodic passage of groups of animals

(especially birds or fishes) from one region to another for feeding or breeding.

What forces drive the changes in a population?

What forces drive the changes in a population?

Why do animals migrate? Avoid harsh and dangerous winter climates Avoid lack of food during winter

– Especially insect or fruit eating birds. Migrate from area of sparse or no food to area of

relatively abundant food So migration increases their chances of survival of

many populations.

*Biology Online Defintions

1) Genetic Drift:– “The process of change in the genetic

composition of a population due to chance or random events”.*

What forces drive the changes in a population?

Examine the figure above.

What is happening to the population of beetles over time?– The number of green beetles are decreasing because they were

eaten or could not reproduce and pass on the genes.

– Overtime, the population will have more of one gene (brown) over the other (green). This is called ‘Genetic Drift’

What forces drive the changes in a population?

4) Natural Selection:– A process in nature in which organisms

possessing certain genotypic characteristics that make them better adjusted to an environment tend to survive, reproduce, increase in number or frequency, and therefore, are able to transmit their essential genotypic qualities to succeeding generations.

What forces drive the changes in a population?

What does all that mean?– Simply that what ever characteristic they had,

It helped them survive in the environment, and will be passed onto their babies in their genes.

What forces drive the changes in a population?

All of the modes shown during this lesson that helped the organism survived will, in the long run, cause changes in the population and thus…

What forces drive the changes in a population?

Evolution

Go on to the next lesson and practice some the mechanisms of evolution mentioned in this lesson.

What forces drive the changes in a population?

Definitions:– Biology Online Definitions:

http://www.biology-online.org/dictionary/

What forces drive the changes in a population?