Ch.7 - Genetic transfer and Mapping in Bacteria Flashcards
Bacteria are…but can be….
haploid, partially diploid (merodiploid)
Bacterial Conjunction
Lederberg & Tatum; Originally was thought bacteria was clonal but is actually a sexual process; E.coli only contains the essential elements and carbon source
What is the difference between Prototroph and Auxotroph?
Prototroph: organism that can grow on a minimal medium that only contains the essential elements and a carbon source, such as a sugar
Auxotroph: organism that cannot grow on a minimal medium that only contains the essential elements
and a carbon source because it contains a defect in the biosynthetic pathway that makes amino acids,
bases, vitamins or cofactors
What is Positive Selection? Name 3 examples of it
The ability to select for one microorganism over a second microorganism; Metabolites: only his+ will grow because it requires histidine; Catabolites: lac- strain won’t grow because it cannot use lactose as a carbon source; Antibiotics: STRS strain won’t grow because it is sensitive to streptomycin
Lederberg Tatum Experiment
They mixed strains with different auxotrophs to get a new strain that grew - recombination was occurring
What is Hfr? What is F+ and F-?
Hfr: sex factor is inserted
into the chromosome of the male and replicates with the chromosome
F+: the sex factor is independent of the chromosome and exists as an episome or plasmid that replicates independently of the chromosome
F-: female cell that lacks a sex factor.
What happens when a F+ male mates with a F- female? What happens when a Hfr male mates with a F- female?
the F- female cell becomes F+ male cell; When an Hfr male cell mates with a F- female cell, the female usually stays F- unless it is a long period of mating, then it can become a Hfr male cell
What did Wollman and Jacob discover?
Hfrs could be used as a mapping tool in E.coli - they did this by mixing 2 strains then put the mixture in a blender to separate the DNA and then placed on agar to see where growth was (which cell). Took 90 mins to complete but was adjusted to 100 mins.
Bacterial Transduction
Phage DNA (virus) digest host genome and package their replicated DNA in host DNA by chopping it up and injecting theirs into it and the DNA is recombined
Bacterial Transformation
The process by which a bacterium will take up extracellular DNA released by a dead bacterium discovered by Frederick Griffith
What are the 2 types of Bacterial Transformation?
Natural transformation: DNA uptake occurs naturally
Artificial transformation: Discovered by Cohen, DNA uptake occurs with the help of experimental techniques that modify the bacteria
-chemical transformation method cells are treated with calcium chloride and a high temperature shock
-electroporation method, cells are washed to remove ions and resuspended in glycerol to provide neutral osmotic support, then subjected to a high voltage low amperage external electrical field
Horizontal Gene Transfer
an organism receives genes from another organism without being a direct offspring
* Horizontal gene transfer can occur via conjugation, transduction and transformation
* Horizontal gene transfer can occur within and also between species acquired
antibiotic resistance
