Lesson 9 - Changing population characteristics

Question 1

Selection pressures:

Answer 1

• Affect the organism’s chances of survival or reproductive success.

Question 2

Natural selection steps:

Answer 2

1. … through the process of natural selection.
2. New alleles are the result of random mutations within their DNA. This creates variation in the gene pool.
3. Some of these mutations provide …
4. Selection pressure conveys an advantage to organisms with the new allele.
5. When selection pressure … survive and reproduce. … pass on their advantageous allele to their offspring.
6. Over time, … allele frequency increases in the population because they have a survival advantage. This process can lead to evolution of a new species over many generations.

Question 3

Antibiotic-resistant bacteria

Answer 3

Methicillin-resistant (MRSA) developed resistance to many antibiotics.
- Bacteria reproduce rapidly and so evolve over relatively short period of time.
- DNA can be altered when bacteria replicate. This usually results in the bacteria dying.
- A mutation in some S. aureus arose that provided resistance to methicillin.
- When exposed to the antibiotic, resistant individuals survived and reproduced, passing allele for resistance onto their offspring.
- Non-resistant individuals died.
- Over time, the no. resistant individuals increased.

Question 4

Peppered moths

Answer 4

• Used to be pale
• Trees became darker due to soot and loss of lichen cover.
• Dark peppered moths survived and reproduced, increasing the frequency of dark moths in the population.
• Clean Air Act 1956 —> trees becoming lighter and the frequency of pale gene has increased.

Question 5

Sheep blowflies:

Answer 5

• Lay eggs in faecal matter around a sheep’s tail - the larvae then hatch and cause sores. Fatal for sheep.
• Pesticide diazinon (organophosphate pesticide) used to kill blow flies and prevent condition.
• Blowflies developed resistance to diazinon.
• Performed investigation with malathion (another organophosphate pesticide) and found resistance alleles in both the old and modern blowflies. Pre-existing resistance.
• Pre-adaptation (when organism’s existing trait is advantageous in new situation.

Question 6

Flavobacterium

Answer 6

Live in waste from factories that produce nylon 6.
- Toothbrushes and violin strings,
- Strain of bacteria digest nylon. Beneficial to humans to clear factory waste.
- Use enzymes nylonases.
- Unlike bacteria found in other strains of Flavobacterium.
- Source of nutrients.
- Believe this is a result of gene duplication / frameshift mutation.

Question 7

Role of pre-adaptation

Answer 7

Can be used by scientists to predict resistance.