Syllabus contente) Evolution occurs via natural selection: ■ individual organisms within a particular species may show a wide range of variation because of differences in their genes ■ individuals with characteristics most suited to the environment are more likely to survive to breed successfully ■ the genes that have enabled these individuals to survive are then passed on to the next generation.f) Where new forms of a gene result from mutation there may be relatively rapid change in a species if the environment changes

B1 7.3 Natural selection

Text p.126

Starter

• Simpsons chameleon• How has it become adapted?

How does natural selection work? Read p126

• It works by selecting the organisms best adapted to a particular habitat

• Do newspaper activity

Natural selection – key points

• Mutation in DNA changes genes• Individual organisms in a species show a range of

variation because of differences in their genes • Individuals best adapted to their environment are

more likely to survive and breed• Pass on their successful genes to their offspring• Successful genes are in a larger proportion of the

next generation

Text q1-3

What is mutation? List key facts – page 126

• A mutation is a change in the genetic material (DNA)

• The result is a new form of a gene• Mutations occur quite naturally• Mutations introduce variety• In terms of survival, mutations can be very

important as can produce an adaptation that makes an organism better suited to its environment

Natural selection in action

Where new forms of a gene result from mutation there may be relatively rapid change in a species if the environment changes

Modern Example 1 -Evolving oysters text p.127copy and complete with the main stages in natural selection

A disease killed most of the Oysters in Malpeque Bay, Canada

Key word: mutation

Key idea: survive to breed

Malpeque Bay Oysters answersA disease killed most of the oysters in Malpeque Bay, Canada

Fortunately a few of the shellfish (oysters) carried a mutation in their genes which made them resistant to the disease. (better adapted)

The organisms with the mutation were the only ones to survive and breed passing on their successful genes to the next generation.

Repeated over generations. So the successful gene is now common in the population.

How did the environment change??

Example 2 - The peppered moth

• The peppered moth is a common insect in Britain with two forms: the dark form and the light form.

• The light form has small black specks just like it has been dusted with pepper. This is variation.

300 years ago most peppered moths were the light form.

After the industrial revolution the dark form became commonest in city areas.

E-chalk animation

Evesham highechalk

Natural selection of dark form in industrial areas

Dark moths more likely to survive to breed- Passing on genes to offspring

Repeated over generationsPopulation contains more dark ans less light moths

Dark moth less likely to be seen and eaten by bird predators- Better adapted to environment

Tree surfaces are dark because of air pollutionPale lichens are killed by sulphur dioxide

Natural selection of light form in clean areas

Light moths more likely to survive to breed- Passing on light genes to offspring

Repeated over generationsPopulation contains a larger proportion of lighter moths

Light moth less likely to be seen and eaten by bird predators-better adapted to the environment

Tree surfaces are pale.Pale lichens grow on the tree bark.

Two varieties of peppered moth

The proportion of dark and light peppered

moths found in different areas of

Britain today.

Due to natural variation, the ancestors of modern giraffes would have had necks of different length.

How does Darwin’s theory explain a giraffe’s long neck?Example 3 -How the giraffe got its neck

As a result, the long-necked giraffes were more likely to be healthy and live to produce more high-quality offspring.

This, in turn, would increase the chances of their long-necked characteristic (an adaptive trait) being passed on to future generations.

Giraffes with longer necks would have been able to reach more food than those with shorter necks.

Plenary - The evolution of superbugs?

True or false?