5.2 natural selection

5.2: NATURAL SELECTIONWhat is required?

GuidanceStudents should be clear that characteristics acquired during the lifetime of an individual are not heritable. The term Lamarckism is not required.

Understandings• Natural selection can only occur if there is

variation amongst members of the same species.• Mutation, meiosis and sexual reproduction cause

variations between individuals in a species. • Adaptations are characteristics that make an

individual suited to its environment and way of life.

• Species tend to produce more offspring than the environment can support.

• Individuals that are better adapted tend to survive and produce more offspring while the less well adapted tend to die or produce fewer offspring.

• Individuals that reproduce pass characteristics to their offspring.

• Natural selection increases frequency of characteristics that make individuals better adapted and decrease the frequency of other characteristics, leading to changes within the species.

Applications and Skills• A: Changes in beaks of finches on

Daphne Major.

• A: Evolution of antibiotic resistance in bacteria.

What is needed for natural selection to occur?

1. Overproduction of offspring- More offspring produced than the environment can support

2. Variation within the population as a result of meiosis, sexual reproduction, and mutations

3. Struggle for survival- Competition for resources, space, mates, etc

4. Differential survival - Those with higher fitness survive, those with lower fitness generally don’t.

5. Reproduction- Fit individuals reproduce and pass on their characteristics.

as a result of

Random Mutation

Sexual Reproduction

DNA Replicatio

n

Viral infection

Meiosis Random fertilizatio

nRandom assortment

of chromosomes metaphase 1

Crossing over (recombination)

prophase I

Competition for food• finding• catching• opening• digesting

Predation • catching• fighting• avoiding• escaping Parasitism

• invading• avoiding• removing• tolerating

Disease• invading• avoiding• removing• tolerating

Competition for mates• attracting• fighting• fertilising• providing for

Competition for spaces• living space/shelter• nesting• reproductive space

Antibiotic Resistance in Bacteria• Two sources

• Mutations• Plasmid transfer

Homework!

• Plasmid• Pilli/pillus• Plasmid transfer

• Exercises 5-8 on pg 239

• Describe the study done by Rosemary and Peter Grant on the differences in beak sizes of ground finches (Geospiza fortis) from Daphne Major. Explain their findings. How does this support the theory of evolution?

For 5.3• Notes including tables organizing the required organisms

from the Applications for this section (pg 240)• See the worked example on 254• Exercises 9-12