Natural selection and evolution 4.3.9

Question 1

Define gene pool

Answer 1

Total number of alleles in a particular population at a specific time

Question 2

Define allele

Answer 2

The form of a gene

Question 3

Define phenotype

Answer 3

The characteristics of an organism

Question 4

Define genotype

Answer 4

The genetic composition of an organism - the alleles it possesses

Question 5

Give a summary of natural selection

Answer 5

1. A population has some naturally-occurring genetic variation with new alleles created through mutations
2. A change in the environment causes a change in the selection pressures acting on the population
3. An allele which was previously of no particular advantage now becomes favourable
4. Organisms with the allele are more likely to survive, reproduce and so produce offspring
5. Their offspring are more likely to have the alleles, so it becomes more common in the population

Question 6

What is evolution?

Answer 6

A change in form, behaviour or physiology over generations.
A change in allele frequency in a population over time.

Question 7

What must take place before evolution can occur?

Answer 7

Variation

Question 8

What is bioaccumulation?

Answer 8

Occurs when toxins build up - or accumulate - in a food chain. The animals at the top of the food chain are affected most severely

Question 9

How does pesticide resistance occur in insects?

Answer 9

• Pesticides are chemicals designed to kill pests
• If an individual has some form of resistance, then it may survive. This individual may reproduce and pass on the resistance characteristic
• The resistance quickly spreads through the whole population

Question 10

How does antibiotic resistance occur?

Answer 10

1. All bacteria show variation
2. Some are more resistant to antibiotics than others
3. Antibiotics will start to kill some bacteria but not all, resistant bacteria will be unharmed
4. When you feel well or forget to take the antibiotics - this means the last of the bacteria are not killed
5. Because only the ones which are resistant survive - they reproduce and pass on the resistance to their offspring
6. This means the antibiotics cannot kill them e.g. MRSA