Lecture 25 Flashcards
1
Q
Selective agents on Adh:
A
- Alcohol
- Temperature
- Alcohol and temperature
- Something else?
2
Q
Clarke Protocol:
A
- Difference in molecular function must be reflected in fitness differences in postulated selective regime
- Natural populations must be re-examined to seek a comprehensive explanation for observed allele frequency distributions in space and time
- Test your hypothesis by perturbing (changing) allele frequencies in a natural population
3
Q
Fitness in the presence of ethanol:
A
- Population cages AdhF frequency increases to fixation when select with lower concentrations of ethanol
- Mixed success
4
Q
Fitness in the absence of ethanol:
A
- Population cages frequencies converge on an intermediate frequency
5
Q
Chateau Tahbilk Winery:
A
- Populations of dros. in the cellar and outside are separate for most of the year
- Once a year there is massive unidirectional gene flow from outside via the fermentation area in the cellar
- This replenishes cellar population
6
Q
What are the conditions in the Tahilk winery?
A
- Range from 8 - 22 degrees
- The population is temperature dependent, and stop breeding at 15 degrees
- Most flies die over winter and there are tiny sub-populations on each vat
7
Q
Evidence for natural selection:
A
- Parallel clines over 5 continents of the S allele decreasing further away from the equator
- Selection for the fast allele in low alcohol environments in cages, selection for a polymorphism even in the absence of alcohol
- Lack of fluctuation in allele frequencies when population size crashes
8
Q
Chateau Tahbilk Overview:
A
- Returned to the pre-perturbation levels
- Returned at a rate which was proportional to temperature/ADH activity relationship
9
Q
Perturbation Experiment 1:
A
- Release a large population of flies into the cellar 1 with an increased frequency of Adh-F
- Same thing done in cellar 2 with a decreased frequency of Adh-F
10
Q
Balancing selection maintains F/S polymorphism:
A
- Lack of noise in allele frequencies in face of potential for drift
- Perturbation experiments
- Parallel clines
- Environmental heterogeneity
11
Q
Problems with the conclusions drawn:
A
Unable to generate consistent fitness estimates for the three genotypes
- Type of balancing selection unclear
- Cannot define the selective agent
12
Q
For other systems:
A
- Parallel clines can be found
- Selective agents are generally unidentified
- Fitness differences between genotypes are extremely difficult to demonstrate
- Detailed studies of inividual populations has not been done
13
Q
Clarke approach:
A
- Choose gene
2. Attempt to find the selective agent
14
Q
The reverse to the Clark approach may be more useful:
A
- Choose a selective agent which has an impact on viability eg) heat stress, insecticides, ethanol tolerance
- Identify gene(s) responsible for adaptation (mapping/DNA seq, candidate gene approach)
15
Q
Benefits of using bacteria for studies:
A
- Allozymic variation exists
- Short generation time
- Population size is near infinite (drift effects are minor)
- Defined cultural medium, so the environment is controlled and manipulated
- Different alleles can be introduces into an identical background using transduction
- Haploid, no heterozygotes
