Question

Touch-down PCR is another modification. Its characteristics include:

(a) Lowering the temperature for primer annealing

(b) Primer annealing is done at higher temperatures initially

(c) The temperature is abruptly reduced in the second cycle

(d) In earlier cycles less stringent conditions are there and in later cycles, more stringent conditions are there

This question was addressed to me in homework.

Question is from Modifications in PCR topic in chapter Polymerase Chain Reaction of Genetic Engineering

Answer 1

Correct option is (b) Primer annealing is done at higher temperatures initially

Easy explanation: It is done in order to overcome the slight mismatch which takes place at lower temperatures. For this, initially the temperature is kept very high and it is reduced in further cycles. As the temperature is reduced, a stage is reduced at which correct primer-template binding is possible but not the incorrect one. In this, in the earlier cycles more stringent conditions are there and in later cycles less stringent conditions are there.