directional selection

Question 1

Directional selection is

Answer 1

natural selection that produces a gradual change in allele frequencies over several generations

Question 2

When does directional selection usually happen

Answer 2

This usually happens when there is a change in environment/selection pressures or a new allele has appeared in the population that is advantageous

Question 3

example of directional selection

For example, antibiotic-resistant bacteria strains are becoming more common due to the overuse of antibiotics

The presence of antibiotics is a selection pressure
Mutations are occurring in bacteria populations randomly

A mutation arises that confers antibiotic resistance - it is a beneficial allele

Bacteria with this mutation are more likely to survive and reproduce
Most bacteria without the resistance mutation die

Over generations, this leads to an increase in the frequency of beneficial allele that produces antibiotic resistance

Question 4

Directional selection favours ……….. phenotype

this means mean trait …… over time

Answer 4

one extreme

changes

Question 5

Exam Tip
Become familiar with the shapes of the graphs above. They can help you answer questions about the type of selection that is occurring in a population.