Investigating Selection

Question 1

Give two types of natural selection

Answer 1

1. Stabilising selection
2. Directional selection

Question 2

What is direction selection?

Answer 2

Where individuals with alleles for characteristics of an extreme type are more likely to survive and reproduce

Question 3

Explain how antibiotic resistance shows directional selection

Answer 3

1. Some individuals have alleles that give them resistance to an abx
2. The population is exposed to the abx, killing bacteria without the resistant allele
3. The resistant bacteria survive and reproduce without competition, passing on the allele that give abx resistance to their offspring
4. After some time, most organisms in the population with carry the abx resistant allele

Question 4

What is stabilising selection?

Answer 4

Where individuals with alleles for characteristics towards the middle of the range are more likely to survive and reproduce

Question 5

Explain how human birth weight shows stabilising selection

Answer 5

1. Humans have a range of birth weights
2. Very small babies are less likely to survive - hard to maintain body temp
3. Giving birth to large babies can be difficult, so they’re less likely to survive
4. Conditions are more favourable for medium-sized babies - so weight of human babies shifts towards the middle of the range