1.7) Evolution

Question 1

• What is ‘natural selection’?

Answer 1

• The non-random increase in frequency of DNA sequences
  ➞ that increase survival
• The non-random reduction in the frequency of deleterious sequences.

Question 2

• What is ‘STABILISING selection?

Answer 2

• An average phenotype
  ➞ is selected for
  ↳ and the extremes of the phenotype range are selected against.

(leads to decrease in genetic diversity - occurs when there is no change in environmental conditions)

Question 3

• What is ‘DIRECTIONAL selection’?

Answer 3

• One extreme of the phenotype range
  ➞ is selected for.

(trait selected will become more common over time due to advantages provided - occurs when there is a change in environmental conditions)

Question 4

• What is ‘DISRUPTIVE selection’?

Answer 4

• Two or more phenotypes
  ➞ are selected for.

Question 5

• What is ‘horizontal transfer’?

Answer 5

• Horizontal gene transfer
  ➞ where genes are transferred between individuals in the same generation.
• Vertical gene transfer
  ➞ where genes are transferred from parent to offspring
  ↳ as a result of sexual or asexual reproduction.

Question 6

• What is the benefit of horizontal transfer?

Answer 6

• Natural selection
  ➞ is more rapid in prokaryotes.
  ↳ This is because prokaryotes can exchange genetic material horizontally,
  ➜ resulting in faster evolutionary change (compared to organisms that only use vertical transfer)

Question 7

• What is the role of an isolation barrier?

Answer 7

• Role of isolation barrier in speciation
  ➞ is important
  ↳ as it prevents gene flow and interbreeding between sub-populations.

Question 8

• What is ‘allopatric speciation’?

Answer 8

• Allopatric speciation
  ➞ when new species arise
  ↳ due to isolation of a population by geographical barriers
  ➜ (e.g. rivers, mountains ranges - isolate populations of animals and plants)

Question 9

• What is ‘sympatric speciation’?

Answer 9

• Sympatric speciation
  ➞ when new species arise
  ↳ despite occupying the same geographical area.

➜ Ecological barriers:
* (whilst not geographically isolated, are isolated by occupying different habitats of varying temperature, pH or salinity.

➜ Behavioural barriers:
* (a population may carry out complex mating rituals that may create a barrier to reproduction)