A gene was cloned into a vector that carries ampR and a lacZ gene with the cloning site inside it…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
A gene was cloned into a vector that carries ampR and a lacZ gene with the cloning site inside it. The cells were plated on ampicillin with a chromogenic substrate. colonies grew, and of them are blue.
- How many colonies are white?
- What share of the colonies are recombinants?
- A student picks a blue colony to grow more of the cloned gene. What is wrong?
Need a reminder? The key ideaShow
The selectable marker finds the transformants. Insertional inactivation finds the recombinants. A foreign gene in the BamHI site of tetR gives colonies that grow on ampicillin and not on tetracycline. In a lacZ vector, white colonies are the recombinants.
The worked solution
Have you tried it?
Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.
Given. colonies, blue.
Plan. White colonies have lacZ broken by the insert. They are the recombinants.
Step 1. (a) white colonies.
Step 2. (b) per cent.
Step 3. (c) A blue colony has a working lacZ gene, so its plasmid has no insert. It does not carry the cloned gene.
Answer: colonies; per cent; the blue colony has no insert.
Check. The two colours make .
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