9.4 Types of selection

Question 1

What is selection?

Answer 1

The process by which organisms that are better adapted to their environment tend to survive and reproduce

Question 2

Key points of directional selection (2)

Answer 2

• Alleles for characteristics at the extremes of a range are favoured
• happens with environmental changes

Question 3

Key points of stabilising selection

Answer 3

• Alleles with characteristics towards the mean are favoured
• happens in a stable environment

Question 4

Example of directional selection:

Answer 4

Antibiotic resistant bacteria

Question 5

Antibiotic resistant bacteria selection:

Answer 5

• variation is present in a population of bacteria
• random mutation = new allele of a gene
• formation of new protein
• enzyme = resistant to a specific antibiotic
  When exposed to antibiotic
• those with mutation have an advantage
• greater reproductive success
  = frequency of antibiotic resistant allele increases

Question 6

Example of stabilising selection

Answer 6

Human birth weight

Question 7

Why is mortality rate higher at the extremes of birth weight?

Answer 7

Very low
- increase SA:Vol
- harder to maintain temp
- increase pressure on heart and lungs

Very high
- difficulties giving birth

Baby less likely to survive