Week 2

Question 1

What is selection?

Answer 1

The process of determining which cells are transformed with a plasmid (that contains a selectable marker on it).

Selection only tells you about which cells have taken up a plasmid, usually nothing about whether that plasmid is recombinant or not

Question 2

Which method(s) are commonly utilised for selection?

Answer 2

1.Antibiotic resistance
2.Restoration of function (e.g. amino acid synthesis)

Question 3

You conduct a cloning and transformation procedure using antibiotic resistance as your selectable marker, and blue/white screening. You plate out your cells on some LB agar containing the relevant antibiotic, X-gal and IPTG. After the appropriate incubation time you observe a mixture of blue and white colonies growing on the plate (similar to that seen in the image).

Which cells are transformants?

Answer 3

All of the colonies.

The white colonies will be those which have take up a plasmid with the antibiotic resistance gene, and the plasmid will contain the insert, therefore it will NOT have a functioning B-galactosidase and will NOT be able to break down X-gal into that blue pigment. These cells WILL be transformants, but not the only ones.