Bio 4600 Exam 2

Seite 1

AZT resistance at phenotypic level

1. random mutation causes change in active site of reverse transcriptase

2. reverse transpritase mistaakes AZT for Thymidine

3. Transcription still happens; enzymes replicate and become main strain when AZT present

Natural Selection Postulates

1. variability within populations

2. variability inherited

3. More offspring reproduced than can survive

4. Survival and reproduction not random. Favorable traits reproduce more

Characteristics of Natural Selection

1. Over time, organisms best adapted survive and reproduce more

2.Frequency of favorable traits go up as you reproduce more

Evolution vs Natural Selection

1.Natural selection causes evolution

2.Evolution:genetic composition change and allele frequency over time

e.g Increase in AZT resistant HIV over time

Mutations

1. Change in genome of organism that can or cannot be phenotypic

2. Occur any time

3. They stop proteins from folding-- protein loses function

4. random mutation before AZT was present, enzyme can detect AZT

Treat a person with HIV in a way less likely to resistant HIV

1. create different treatments that interfere at every stage of the virion replicating cycle

Once one resistance strain is predominant, move on to the next cylcle with different treatment

Adaptation, Fitness, Population

Adaptation: trait that increases fitness relative to others without the trait

Fitness: ability to survive and reproduce in an environment

Population: group of organisms that interbreed and live in same place at same time

Negative Frequency dependent Selection

Organisms with rare frequencies survive longer bc better adapted until frequency changes

e.g scale eating fish

Multi Level Selection

1. Natural selection happens at group level

2. Within one host: put most alleles in NEXT generation of HIV

3.Amongst pop in group: Successfully affects host for transmission

Evolutionary Trade offs

No traits are optimal. There are costs and benefits . One increases the other.

e.g brain size would cause painful birth

HIV trade off

High virulence= host may die before passing virus after copying

Low virulence= might not be passred on to copy

AZT resistance slows down reverse transcriptase, so if all resistant to AZT and the treatment is over then they wont be as effective as otherwise

Sex Practices for higher or lower HIV virulence

1. Person mates frequently, better for high virulence so virus can be spread, even if for short period

2. monogamy better for low virulence bc host needs to be alive long enough to pass on