L33 DGRP Flashcards
DGRP
see onenote
Drosophila Genetic Reference Panel
- set of 192 inbred lines
- living library of common polymorphisms
Screening DGRP with imidacloprid
see onenote
Wiggle index
- Measuring decrease of movement upon insecticide exposure, measure of intoxication
- The higher the ratio, the less effected the individuals are and vice versa
Many genes contribute to resistance phenotype
see onenote
- several of the candidate genes involved in development and function of nervous system
Conclusions
see onenote
4 points
Selection in bacteria
see onenote
Chemostat experiments
- strains with different alleles competed pairwise
- T5 bacteriophage resistance used as a marker, can assay for bacteriophage resistance
- reciprocal experiments with T5 marker
Growth rate
see onenote
growth rate = fitness
growth rate of two strain in chemostat is a measure of relative fitness
Dykhuizen and Hartl (1983)
- 5 PGI alleles competed pairwise
- activity of PGI allozymes differed when measured under chemostat conditions
- chemostat competition for limited supply of glucose
Observation
- within limits of detection, no selection i.e. neutral
- one allele => decreased growth with limiting fructose
Glucose was the limiting resource
- Environment should’ve been selective BUT we didn’t see it
- There is selective neutrality, selection is being imposed but there is no difference in fitness between the phenotypes
Silva and Dykhuizen (1993)
- competed strains with six different “natural” lac operons
- competed for lactose or one of 3 different beta-gal substrates which were not normally encountered
- very small fitness differences on lactose (near neutral)
- much larger fitness differences on other substrates
MGP vs lactose
see onenote
Plot of selection coefficient for atypical sugars (MGP) vs selection coefficient in a lactose environment
- Selection coefficient for the difference strains between 0 - 0.05 on lactose axis, much bigger range on MGP axis
lactulose vs lactose
see onenote
Gal-ara vs lactose
see onenote
Much bigger selection on Gal-ara axis in comparison to lactose axis
Lactose is the common sugar, E.coli naturally encounters it. Minimal selection when lactose is limiting, E.coli has adapated to it.
When confronted to an environment where the sugar is rarely encountered, see large selection coefficient at the beta-gal locus in the beta-gal gene
Charles Darwin definition of fitness:
Relative fitness of a genotype in a particular environment
This is an extreme environment, in nature, in benign environment, you don’t see very strong selection.
Can be selectively neutral in a benign environment but not selectively neutral in a more extreme environment
Dykhuizen, Dean and Hartl (1987)
- competed strains with different lac operons against a lacI- strain in conditions where:
1. lactose limiting
2. various levels of IPTG induction - measured beta-gal and permease activity
- different outcomes for two enzymes - why?
Permease vs beta-gal activity
see onenote
Permease
- Transporter
- Why does increase in permease increase fitness but beta-gal increase does not increase fitness
- Even at lower levels there is enough beta-gal activity to deal with as much lactose that can be brought in by permease
- Permease activity is rate limiting, if you can bring more lactose into the cell as there’s always enough beta-gal to convert it into sugar energy, the fitness will increase
- The amount of glucose and galactose produced (the flux) changes due to permease activity
- Permease is the rate limiting enzyme
Metabolic control theory
- Kacser and Burns
- provides link between enzyme kinetics and fitness
- overall flux through a pathway the important consideration for fitness
- some steps in the pathway have greater impact on flux than others
- theory expressed in terms of model based of measurable kinetic parameters
Implications
- relative fitness differences between genotypes zero => extremely small
- relative fitness values vary between environments - neutral in some, not in others
- selection may be stronger in extreme, atypical environments
- pathway flux could be critical for fitness - selection may operate on whole pathways (groups of genes)
