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Several Tricks are Used to Detect Recombinants
- The recombinant plasmids are put into bacteria so that multiple copies can
be made
- When the bacteria divide the plasmids divide too
- If bacteria are diluted and grown on agar plates they will form round
colonies
- Each colony is a clone derived from a single cell
- Tricks are used to find colonies with DNA inserts
- Trick 1: plasmids with a gene that gives resistance to the antibiotic
ampicillin are used
- If the bacteria are grown on agar plates containing ampicillin only
bacteria with a plasmid can grow
- Trick 2: DNA is inserted at a restriction site in the middle of a
beta-galactosidase gene (Lac
Z)
- If DNA is inserted the gene is destroyed
- Bacteria with beta-galactosidase gene can convert an artificial
substrate, X-gal, into a blue dye
- If the colonies are given X-gal those without recombinant DNA will be
blue (their gene works) and those with recombinant DNA will be white
(their gene has been destroyed)
The Nuclear DNA Can be Cut up to Make a Genomic DNA Library
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