Module 5: Bacterial Genetics (Basics) Flashcards
Advantages of using bacteria in genetic research
1) Each cell is a complete organism
2) Usually grow rapidly
3)Simple genomic organization
Bacterial growth is measured by…
NUMBER of cells (NOT by the change in size of cells)
In what way do bacteria have a simple genomic organization?
Usually only contain ONE copy of their genome
–> Each gene exists as a single copy within the larger genome
How does the organization of bacterial genome make it ideal for genetic research?
No mutation masking
–> A mutation in a gene will often produce a readily observable phenotype (because there’s only one copy of the gene)
Why are bacteria “better” than eukarya for genetic research?
Bacteria = 1 copy of genome
Eukarya = 2 copies of genome
–> A mutation in one copy of a gene can get “masked” by the second copy being the WT variant == Harder to observe an induced mutation!
Why were microbial genetics limitedly studied in history?
1) It was believed that bacteria (and other microbes) were “too small/simple” to have a system of genetic exchange
2) Nobody had observed inheritance of phenotype in bacteria
What was the major objective of Joshua Lederberg’s work with nutritional mutants?
To examine if gene transfer could occur between bacteria
–> Did so by studying nutritional mutants of E. coli
Nutritional Mutant
AKA. Auxotroph
Organisms with altered metabolic requirements
–> typically have mutations which disrupt specific metabolic pathways
What auxotrophs did Joshua Lederberg study?
2 auxotrophs of E. Coli:
1) Met+ Pro- (could produce methionine but not proline)
2) Met- Pro+ (could produce proline but not methionine)
Growth conditions for: Met+ Pro-
Media supplemented with proline
(Can’t produce it)
Growth conditions for: Met- Pro+
Media supplemented with methionine
(Can’t produce it)
Phototroph
= PARENTAL STRAIN (Wild type; WT)
–> Grows on simple defined growth medium (w/ proper sources of C, N, P)
–> No supplementation required for growth!
Auxotrophic Mutations typically…
Make organisms unable to synthesize AAs and vitamins (that are produced within + required for parental strain growth)
Auxotrophs will only grow if…
The AA or vitamin they cannot produce is supplemented into the growth medium they are grown in
Met- auxotrophs only grow in…
Medium WITH methionine
(Because they can’t produce it)
Pro- auxotrophs only grow in…
Medium WITH proline
(because they can’t produce it)
WT, Met-, Pro- Growth In:
Media with Met + Pro
ALL GROW
–> WT, MET- PRO-
WT, Met-, Pro- Growth In:
Defined media
WT GROWS
–> Met- and Pro- do not grow
WT, Met-, Pro- Growth In:
Media with Pro
WT + PRO- grows!
MET- can’t grow
WT, Met-, Pro- Growth In:
Media with Met
WT and MET- grows
Pro- can’t grow
What was Lederberg’s hypothesis/prediction (for auxotroph experiment)?
If TWO auxotrophs were cultured together and produced progeny that could thrive on media WITHOUT nutrient supplement, the transfer of genetic material between auxotrophs will have occurred
What unexpected outcome did Lederberg observe with his control experiment?
(What was the control experiment?)
Experiment:
–> Individually plated WT, met-, pro- cultures onto plates with regular medium
Expected Results:
–> ONLY WT plate would display growth
Actual Results:
–> WT, met-, AND pro-cultures all grew!
What was the cause of Lederberg’s unexpected control experiment results?
REVERSION
–> The reversion rate was too high
(spontaneous mutation)
Reversion
Spontaneous recovery of a mutant to perform an action/function
–> Essentially, a spontaneous mutation that allows a once-mutant to REGAIN a specific ability