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Horizontal Gene Transfer
Term used to describe any method where bacteria share genetic information with each other. It is one of the main causes of the spread of antibiotic resistances among bacteria, but it is also utilized by microbiologists for genetic manipulation of bacterial cultures
3 methods include:
Transformation
Conjugation, and
Transduction
Vertical Gene Transfer
Where genetic information is passed from parent to offspring
Bacterial Transformation
Process by which a recipient bacterial cell takes up DNA from its environment
Competence
The ability of a bacteria or other microorganism to take up DNA from its environment
Chemically competent transformation
Plasmid DNA is mixed with cold cells that have been treated with calcium chloride (CaCl2), which alters the cell membrane to make it more permeable to DNA, in addition to counteracting the negative charge of DNA molecules
Cells are then exposed to a high temperature for a short period of time, called a heat shock, which briefly disrupts the cell membrane and allows the plasmid DNA to enter
Cells are then put back on ice, provided nutrient broth, and left to recover.
During this recovery period, bacteria that have taken up the plasmid will start to replicate it and express the genes within – in our case, resistance for the antibiotic ampicillin
Plasmid
An extrachromosomal circular DNA element that can replicate independently of the bacterial host chromosome (recall that prokaryotic cells contain a single, looped chromosome)
Allow for horizontal gene transfer between bacterial cells and may confer selective advantage under stressful conditions
Positive Control
Show how results would look if an experiment worked properly
If your experiment’s positive control does not produce the expected result, that is an indication there may be an issue with the protocol or a confounding variable you forgot to address
Negative Control
Show what the result of an experiment would be if it did not work
If you get a positive result in your positive control AND a positive result in your negative control, that indicates there is some confounding variable you did not address