Topic 4—B: Biodiversity and Selection- 5. The effects of selection

Question 1

What are the types of natural selection?

Answer 1

• Directional selection
• Stabilising selection

Question 2

What is directional selection?

Answer 2

Where individuals with alleles for characterises of an extreme type are more likely to survive and reproduce. This could be a response to an environment change

Question 3

What is stabilising selection?

Answer 3

Where individuals with alleles for characteristics towards the midline of the range are more likely to survive and reproduce. it occurs when the environment isn’t changing and it reduces the range of possible characteristics

Question 4

What is an example of directional selection?

Answer 4

Bacteria evolving antibiotic resistance
- some individuals in a bacterial population have alleles that give them resistance to an antibiotic.
- the population is exposed to the antibiotic killing bacteria without the resistance allele.
- the resistant bacteria survive and reproduce without competition passing on the allele that gives antibiotic resistance to their offspring.
- after some time most organisms in the population will carry the antibiotic resistance allele

Question 5

What is an example of stabilising selection?

Answer 5

• very small babies are less likely to survive as they have a large surface area to volume ratio which means they find it hard to maintain their body temperature.
  very large babies are less likely to survive too as their size makes it hard for them to fit through the mothers pelvis.
  conditions are most favourable for medium sized babies