Evolution and Medicine

Question 1

Explain how by comparing DNA sequences we can understand their relationship

Answer 1

• Using PCR you can isolate viral genomes, or pieces of viral genomes, from infected patients.
• By comparing these we can see where there are changes; where the changes are shared and where the changes are different. This helps us work out the relationships between species.
• By using phylogenetic trees we can see that the more changes there are between individuals, the further apart they are.

Question 2

Explain how we can predict that the HIV virus is changing

Answer 2

• Evidence for: Viruses within a patient are more similar than between. The pattern of the tree suggests that a single point entry of a virus, and then diversification.
• Evidence against: patient 91 has a virus in two parts of the tree.
• Prediction: If the viruses are changing then if we sample a patient successively then we should see different viral sequences appearing.

Question 3

Proximate vs Ultimate

Answer 3

Proximate:
- By what mechanism is the change occurring

Ultimate:
- What is causing the change

Question 4

Describe reverse transcription

Answer 4

• Reverse transcriptase is an enzyme that turns RNA sequence back into DNA
• The HIV genome is RNA, but is turned into DNA to insert in the genome
• Reverse Transcription is more error prone than DNA replication, so lots of variants are formed…

Question 5

What are the selective pressures HIV is under?

Answer 5

• The immune system
• Drug regimen
• Changes in the receptor
• Tropism in tissues
  However, the virus still survives because it replicates so quickly and makes so many variants due to its errored replication technique. The variants allow it to resist these selective pressures bc it is more likely there will be a variant that can survive the pressure.
• Many organisms evolve within a host in the same way.

Question 6

Describe evolution and medicine

Answer 6

• Evolutionary thinking can help us understand and better respond to pathogens like HIV
• Evolution is a key-way that pathogens respond to hosts and therapy
• This is just one instance where evolution is part of our understanding of disease.

Question 7

What is the role of evolutionary change in the virulence of pathogens?

Answer 7

• The antibiotic resistance spreading through a population is also an evolutionary process.
• Even our own genome evolves in response to pathogens
• So many pathogens evolve within a host in this way.