Define a probe and explain how probes are used in colony hybridization experiments. What will be ...

ANSWER: A probe is usually a single-stranded DNA of defined sequence that is distinctively labeled with some easily detectable marker, such as a fluorescent tag. The nucleotide sequence of the probe is designed to be complementary to the sought-for or target DNA fragment. To detect a colony that contains the desired DNA, the prehybridized sheet is incubated in a sealed plastic bag with a solution of specific probe molecules. The single-stranded probe DNA anneals with the single-stranded target DNA bound to the sheet through specific base pairing to form a DNA duplex. This annealing, or hybridization as it is usually called, labels the target DNA, revealing its location.